Bio 3

Question 1

3.1 Define the term
gene.

Answer 1

A gene is a heritable factor that consists of a
length of DNA and influences a specific
characteristic.

Question 2

3.1 Outline the
relationship
between a gene
and a chromosome.

Answer 2

A gene occupies a specific position on a
chromosome; this specific position is called locus.
Genes can be linked into groups, and each group
= one tvpe of chromosome.

Question 3

3.1 Define alleles,
and outline how it is
formed.

Answer 3

Alleles are the various specific forms of a gene.
New alleles are formed by mutation, and they
differ from each other by one or only a few bases
Most animal have 2 copies of each type of
chromosome, and each copy may have same or
different alleles; but only one allele can occupy
the locus of a gene on a chromosome.

Question 4

3.1 Outline the
definition of genome

Answer 4

The genome is the whole of the genetic
information of an organism.
The size of a genome is therefore the total
amount of DNA in one set of chromosomes in that
species. It can be measured in millions of base pairs of DNA.

Question 5

3.1 Application: List
the number of
genes of one plant,
one bacterium, one
species with more
genes and one with
fewer genes than a human

Answer 5

**The number of genes in a species should not be
referred to as genome size as this term is used for
the total amount of DNA.
Estimated number of protein-coding genes in
humans is 21 000.
Escherichia Coli (Bacteria): less genes than
humans
~4 200
Oryza Sativa (Rice): plant, more genes than
humans
~38 000
Gallus gallus (Chicken): animal, less genes than
humans
~1700
Daphina pulex (water flea): animal, more genes
than humans
~31 000

Question 6

3.1 Explain the
causes of sickle cell
anemial

Answer 6

The cause of sickle cell anemia is due to the base
substitution mutation in the DNA.
-in DNA sense strand gene that codes for
hemoglobin protein, GAG is being mutated to
GTG (thymine substituted adenine)
-which then codes for valine instead of glutamic
acid on the SIXTH amino acid.
-this causes a change to the base sequence of
mRNA transcribed from it and a change to the
sequence of a polypeptide in hemoglobin.

Question 7

3.1 Outline the
Human Genome
Proiect and its
outcome.

Answer 7

The Human Genome Project began in 1990 with
the aim of determining the complete sequence of
the human genome and identifying every gene
that it contains.
Gene sequencers is a technique used in gene
sequencing. The sanger process is used, and
fluorescent markers are used to label the DNA
fragments in order to find out the order of the
DNA sequences.
An optical detector is used to detect the colours
of fluorescence along the lane. There is a series
of peaks of fluorescence, corresponding to each
number of nucleotides, and a computer is used to
deduce the base sequences.

Outcomes of the HGP:
knowledge of location of human genes / position
of human genes on chromosomes;knowledge of
number of genes/interaction of genes /
understanding the mechanism of mutations;
evolutionary relationships between humans and
other animals;
discovery of proteins / understanding protein
function / detection of genetic disease;
leads to the development of medical treatment/
enhanced research techniques;
knowledge of the base sequence of genes/study
of variation within genome;

Question 8

3.2 Distinguish
between
prokaryotic and
eukaryotic
chromosomes

Answer 8

Prokaryotes have one chromosome consisting of
a circular DNA molecule, they reproduce
asexually through binary fission. Some
prokaryotes also have plasmids but eukaryotes
do not. Plasmids are used to transfer genetic
information from one bacteria to another. They
are also used in laboratories to genetically modify
a prokaryote.
Eukaryote chromosomes are linear DNA
molecules associated with histone proteins.
In a eukaryote species there are different
chromosomes that carry different genes, with
both coding and non-coding DNA.
Eukaryotes have different types of chromosome
with 2 alleles of each type.

Question 9

3.2 Describe what
homologous pairs
are in relationship
to diploid and
haploid nuclei.

Answer 9

Homologous chromosomes carry the same
sequence of genes but not necessarily the same
alleles of those genes. A same type of
chromosome can be identified by its length and
shape (have same length and same position of
centromere).
Diploid nuclei have pairs of homologous
chromosomes; they have 2 types of
chromosomes, meaning they have 2 genes copies
(alleles) for each trait. A somatic cells are diploid
and divide by mitosis.
Haploid nuclei have one chromosome of each
pair, as they only possess a single copy (one
allele) for each trait. Sex cells are haploid and
they divide by meiosis.

Question 10

3.2 State why
chromosome
number and type is
a distinguishing
characteristic of a
species.

Answer 10

The number of chromosomes is a characteristic
feature of members of a species.
In order to reproduce, the species have to have
the same number of chromosomes in order to
form homologous pairs in zygotes.

Question 11

3.2 Describe the
process of creating
a karyogram, and its
Uses.

Answer 11

-a karyogram shows the chromosomes of an
organism in homologous pairs of decreasing
length.
-a cell is “frozen” in metaphase by the application
of chemicals that disrupt the mitotic spindle.
-a hypotonic solution is added;
-water enters the cell causing it to swell and
burst, separating the chromosomes from each
other.
-the chromosomes are stained and viewed with a
microscope.
-the images of the chromosomes are then
organized in a standard pattern, from longest
chromosomes to the smallest;
-with heterosomes at the end
Karyograms can be used to deduce sex and
diagnose Down syndrome in humans. The 23rd
pair of karyogram reveals the gender.
Down syndrome can be identified as such patients
have 3 copies of chromosome 21 (trimosy 21)

Question 12

3.2 Distinguish
between
heterosome and
autosomes.

Answer 12

Heterosomes are sex chromosomes, they are the
23rd pair of chromosomes. X is big and long, Y is
small and short and contains SRY gene for
development of male characteristics.
Heterosomes are homologous in females (XX) but
not in males (XY)
Autosomes are chromosomes that do not
determine sex (the rest of the somatic cells)

Question 13

3.2 Describe Cairns’
technique for
measuring the
length of DNA
molecules, his
conclusion.

Answer 13

Autoradiography is used through the use of
electron microscopes.
1. Allows bacterium to absorb 3H-Thymidine
(Tritiated thymidine)
-contains tritium, a radioactive isotope of
hydrogen, so radioactively labelled DNA was
produced by replication in the E. coli cells.
2. Cells were then placed onto a dialysis
membrane and their cell walls were digested
using the enzyme lysozyme.
-cells were gently burst to release their DNA onto
the surface of the dialysis membrane.
3. A thin film o photographic emulsion was
applied to the surface o the membrane
-being left in darkness for weeks
-some o the atoms o tritium in the DNA decayed
and emitted high energy electrons, which react
with the film.
-each point where a tritium atom decayed there is
a dark grain.
The film showed that prokaryotic chromosomes
are circular, and the length and width of the
chromosomes can be determined

Conclusions:
-Chromosome in E. coli is a single circular DNA
molecule with a length o 1,100 microm. (the E coli
cells is only 2 microm!)
-prokaryotic chromosomes are circular
-measured the lengths of chromosomes.
-he also observed the DNA replication fork.

Question 14

3.2 Application:
Comparison of
genome size in T2
phage, Escherichia
coli, Drosophila
melanogaster,
Homo sapiens and
Paris japonica.

Answer 14

*genome size measured in # of base pairs
T2 phage:
170 000 bp
Escherichia coli:
4.6 million bp
Drosophila melanogaster:
130 million bp
Homo Sapiens:
3.6 billion bp
Paris japonica:
150 billion bp

Question 15

3.2 Application:
Comparison of
diploid
chromosome
numbers of Homo
sapiens, Pan
troglodytes, Canis
familiaris, Oryza
sativa, Parascaris
equorum.

Answer 15

Homo Sapiens:
46
Pan troglodytes:
48
Canis familiaris:
78
Oryza sativa:
24
Parascaris equorum:
4

Question 16

3.3 Outline the
process of meiosis.

Answer 16

a. meiosis reduces a diploid cell into (four)
haploid cell(s);
b. (during prophase I) homologous chromosomes
pair Up/synapsis;
nuclear membrane degenerates
centrioles move to opposite poles
C. chromatids (break and) recombine / crossing
over followed by condensation.
d. (metaphase I) (homologous chromosomes) at
the equator of the spindle / middle of cell;
e. (anaphase I) (homologous) chromosomes
separate and move to opposite poles;
f. (telophase I) chromosomes reach poles and
unwind WTTE;
Separation of pairs of homologous chromosomes
in the first division of meiosis halves the
chromosome number.
g. (prophase Il) chromosomes (condense and)
become visible, new spindles form;
h. (metaphase Il) chromosomes line up at the
centre of the cells/ equator;
i. (anaphase I) sister chromatids separate;
j. (telophase Il) chromatids reach the poles and
unwind;

Question 17

3.3 What happens
prior to meiosis?

Answer 17

DNA is replicated before meiosis so that all
chromosomes consist of two sister chromatids.

Question 18

3.3 Explain why
meiosis is known as
reduction division?

Answer 18

One diploid nucleus divides by meiosis to
produce four haploid nuclei. The halving of the
chromosome number allows a sexual life cycle
with fusion of gametes to form a zygote with 46
chromosomes (not more or less)

Question 19

3.3 Explain how
sexual reproduction
can lead to
variation in a
species.

Answer 19

allows characteristics from both parents to
appear in offspring;
crossing over (during prophase 1) changes
chromosome composition;
produces gametes which are all different;
random chance of which sperm fertilizes ovum;
greater variation (resulting from sexual
reproduction) favours survival of species through
natural selection;
random orientation of homologous pairs during
metaphase l.
Accept independent assortment during meiosis
from AHL.

Question 20

3.3 Application:
Explain how non-
disjunction can
cause Down
syndrome and other
chromosome
abnormalities.

Answer 20

Non-disjunction is when chromosomes fail to
separate in in meiosis I / chromatids in meiosis II/
anaphase Il;
This causes a sex cell to have one less or one
more chromosomes, which causes the zygote to
have 47 or 45 chromosomes.
Down syndrome can be determined through
identifying the trisomy on chromosome 21 on
karyogram.
Increased probability with increased age of
mother/ages of parents after 35 maternal age
There is a strong correlation between maternal
age and occurence of non-disiunction events.

Question 21

3.3 Application:
Description of
methods used to
obtain cells for
karyotype analysis.

Answer 21

Chorionic villus:
-a sampling that enters through the vagina is used
to obtain cells from the chorion
-one of the membranes from which the placenta
develops.
-the tissue from placenta is collected by entering
a tube through the cervix.
-this can be done earlier in the pregnancy than
amniocentesis, but whereas the risk of miscarriage
with amniocentesis is 1%, with chorionic villus
sampling it is 2%.

Amniocentesis
-involves the removing of amniotic liquid that
surrounds the baby through a long needle
collected through the mother’s abdomen.
-involves passing a needle through the mother’s
abdomen wall, using ultrasound to guide the
needle
-the needle is used to withdraw a sample of
amniotic fluid containing fetal cells from the
amniotic sac.
The miscarriage percentage for the two are:
1% amniocentesis and 2% for chorionic villus.
**pre-natal diagnosis by karyotype analysis is
usually only carried out in mothers over 35
-until then the risk of miscarriage caused by the
procedure is greater than the risk of Down
Syndrome.

Question 22

3.4 Outline why
Mendel’s success is
attributed to his use
of pea plants.

Answer 22

Mendel discovered the principles of inheritance
with experiments in which large numbers of pea
plants were crossed.
-his success was due to him obtaining numerical
values, rather than just descriptions of outcomes.
-Mendel’s use of peas allowed for the
observation of easily distinguishable
characteristics (i.e. yellow or green pods).
-Also, the peas were able to reproduce quickly
allowing for many generations of data to be
collected.
-Lastly, the reproduction could be controlled, so
Mendel knew exactly which two parent plants
were being bred (either cross-bred or self-
pollination).
From his experiment he discovered the presence
of dominant and recessive alleles through
artificial pollination of purebred pea plants.

Question 23

3.4 Explain the
relationship
between meiosis
and inheritance.

Answer 23

The two alleles of each gene separate into
different haploid daughter nuclei during meiosis.
Gametes are haploid so contain only one allele of
each gene.
Fusion of gametes results in diploid zygotes with
two alleles of each gene that may be the same
allele (homozygous) or different alleles
(heterozygous)

Question 24

3.4 Explain
dominant and
recessive allele in
inheritance.

Answer 24

Dominant alleles mask the effects of recessive
alleles but co-dominant alleles have joint effects;
which means (pair of) alleles that both affect the
phenotype when present in a heterozygote / both
alleles are expressed;

Question 25

3.4 List out genetic diseases that are due to autosomal dominant, autosomal recessive, Co- dominant, and sex linked.

Answer 25

Autosomal dominant: Huntington's Disease Autosomal Recessive: cystic fibrosis Co-dominant: Sickle cell anemia ABO Blood groups Sex linked: hemophilia (recessive) red-green color blindness (recessive)

Question 26

3.4 Describe patterns that can be seen regarding diseases caused by autosomal dominant, autosomal recessive, and sex linked.

Answer 26

Autosomal dominant: -every affected individual have at least one affected parent -present in every generation -present in both males and females Autosomal recessive: -cases where both parent are not affected -Skips generation -present in both males and females Sex linked: -more common in males -can only inherit from parent of opposite gender

Question 27

3.4 Explain the rarity of genetic diseases

Answer 27

-often times genetic diseases seem to just "appear" in a family without prior history. -this is usually because the disease is caused by a recessive allele that has been masked by dominant alleles. -if two carriers, who show no disease symptoms, produce offspring, there is a 1/4 change of the offspring showing the disease characteristics. Many genetic diseases have been identified in humans but most are very rare. Most are rare because severe diseases that are caused by homozygous alleles may not survive until reproduction age so they cannot be passed on. Recessive conditions tend to be more common and dominant conditions.

Question 28

3.4 List and explain the factors that increase the mutation rate and can cause genetic diseases and cancer, and apply it to the consequences of nuclear bombing of Hiroshima and accident in Chernobyl.

Answer 28

Radiation and mutagenic chemicals increase the mutation rate and can cause genetic diseases and cancer. Radiation: -the high energy wavelengths can have enough energy to cause chemical changes in DNA. Chemical substances: -smoke and mustard gas that possesses chemical can change DNA. -causing thyroid disease after Chernobyl due to release of radioactive iodine. -250% increase in congenital abnormalities -Reduced T cell counts and altered immune functions, leading to higher rates of infection -caused variation in flora and fauna in Chernobyl

Question 29

3.5 Explain how gel electrophoresis and polymerase chain reaction are used in DNA profiling.

Answer 29

Gel electrophoresis is used to separate proteins or fragments of DNA according to size, and PCR can be used to amplify small amounts of DNA. 1. DNA (specifically the short tandem repeats) is first cut into smaller, separate fragments by the endonuclease. 2. DNA needs to be copied/amplified for DNS profiling. 3. placed in a block of gel where electric current is applied (different fragments will move different distances because it is negatively charged, and each fragment has different size/weight) So smaller samples travel faster and further. 4. DNA profiling: the banding patterns of a person's DNA can be identified (unique to each individual). 5. Comparing DNA profiles can allow paternity and forensic investigations.

Question 30

3.5 Explain how gene modification is carried out.

Answer 30

Genetic modification is carried out by gene transfer between species (the placement of a gene from one species into another and have it expressed). It is possible because the genetic code is universal. Gene transfer to bacteria using plasmids makes use of restriction endonucleases and DNA ligase 1. DNA is isolated from cell via centrifugation and then amplified by PCR. **Bacterial plasmids are commonly used as vectors (DNA molecule that is used as a vehicle to carry the gene of interest) because they are capable of autonomous self-replication and expression. 2. Restriction endonuclease cleave the sugar- phosphate backbone to generate blunt ends or sticky ends. 3. The gene of interest is inserted into a plasmid vector that has been cut with the same restriction endonucleases D 4. DNA ligase joins the vector and gene by fusing their sugar-phosphate backbones together with a covalent phosphodiester bond. 5. The recombinant construct (including the gene of interest) is finally introduced into an appropriate host cell or organism 6. Transgenic cells, once isolated and purified, will hopefully begin expressing the desired trait encoded by the gene of interest.

Question 31

3.5 Define what clones are, and the production of cloned embryos.

Answer 31

Clones are groups of genetically identical organisms, derived from a single original parent cell. Cloned embryos produced by somatic-cell nuclear transfer (nuclear transplantation)- reproductive cloning (not therapeutic cloning with stem cells) 1. Somatic cells removed from adult donor and are cultured. 2. Unfertilised egg is removed from female adult (enucleated - haploid nucleus is removed) 3. Enucleated egg fuses with diploid nucleus from adult donor, forming a diploid egg cell. 4. An electric current is then delivered to stimulate the egg to divide and develop into an embryo 5. The embryo is then implanted into the uterus of a surrogate and will develop into a genetic clone of the adult donor.

Question 32

3.5 Describe some natural methods of cloning.

Answer 32

Many plant species and some animal species have natural methods of cloning. -bacteria reproduce via binary fission - asexual reproduction. -plants reproduce asexually via: -stem cutting: a separated portion of plant stem that can regrow into a new independant clone. -budding: cells split off the parent organism, generating a smaller daughter organism which eventually separates from the parent e.g. Strawberry plants send out stolons, also known as runners, which are horizontal projections that have new plants on the end that can grow into cloned daughter plants. -vegetative propagation: small pieces can be induced to grow independently -identical twins are due to the natural separation of embryo - monozygotic

Question 33

3.5 Describe and explain the two methods of cloning in animals.

Answer 33

Animals can be cloned at the embryo stage by breaking up the embryo into more than one group of cells. -pluripotent cells are separated artificially in the laboratory, each group of cells will form cloned organisms -separation of embryonic cells can also occur naturally to give rise to identical (monozygotic) twins -separated groups of cells are then implanted into the uterus of a surrogate to develop into genetically identical clones -limited by the fact that the embryo used is still formed randomly via sexual reproduction and so the specific genetic features of the resulting clones have yet to be determined -animals such as hydra create clones through a process of budding. -a bud develops as an outgrowth due to repeated cell division at one specific site. -these buds develop into tiny individuals and, when fully mature, detach from the parent body and become new independent individuals. Methods have been developed for cloning adult animals using differentiated cells. -involves somatic cell nuclear transfer (SCNT) -replacing the haploid nucleus of an unfertilised egg with a diploid nucleus from an adult donor -advantage: it is known what traits the clones will develop (they are genetically identical to the donor)

Question 34

3.5 Design of an experiment to assess one factor affecting the rooting of stem- cuttings.

Answer 34

Stem cuttings are typically placed in soil with the lower nodes covered and the upper nodes exposed, where meristematic cells are present to be induced for vegetative propagation. There are a variety of factors that will influence successful rooting of a stem cutting: -Cutting position:whether cutting occurs above or below a node, as well as the relative proximity of the cut Length of cutting (including how many nodes remain on the cutting) - Growth medium (whether left in soil, water, potting mix, compost or open air) - The use and concentration of growth hormones - Temperature conditions (most cuttings grow optimally at temperatures common to spring and summer) - Availability of water (either in the form of ground water or humidity) - Other environmental conditions (including pH of the soil and light exposure)

Question 35

3.5 Assessment of the potential risks and benefits associated with genetic modification of crops.

Answer 35

The genetic modification of crops involves altering the DNA of plants to enhance desirable traits, such as resistance to pests, disease, or drought, or to improve their nutritional value. Like any other technology, there are potential risks and benefits associated with genetic modification of crops. Benefits: Increased crop yields: Genetic modification can improve the productivity of crops, leading to increased yields and reduced food insecurity. Pest and disease resistance: By introducing genes from other organisms, crops can become more resistant to pests and diseases, reducing the need for pesticides and other harmful chemicals. Improved nutritional value: Genetic modification can enhance the nutritional value of crops by introducing genes that increase the levels of vitamins or other essential nutrients. Environmental sustainability: By reducing the need for harmful chemicals and increasing yields, genetic modification can promote sustainable agriculture and reduce the impact of farming on the environment. Risks: Potential harm to human health: There are concerns that genetic modification may introduce allergens or toxins into crops that could be harmful to human health. Environmental risks: There are concerns that genetically modified crops could potentially crossbreed with wild species, creating new and potentially harmful organisms that could damage ecosystems. Reduced biodiversity: Genetic modification can lead to monoculture, where large areas are planted with the same genetically modified crop, reducing the diversity of crops and potentially making them more vulnerable to pests and disease. Ethical concerns: There are ethical concerns surrounding the ownership of genetic resources and the potential impact of genetic modification on small-scale farmers and indigenous communities.

Question 36

3.5 Analysis of data on risks to monarch butterflies of Bt crops.

Answer 36

Bt corn is a genetically modified maize that incorporates an insecticide producing gene froma bacterium. This insecticide is lethal to certain types of larvae, particularly the European corn borer which would otherwise eat the crop. D Concerns have been raised that the spread of Bt corn may also be impacting the survival rates of monarch butterflies -wind-borne pollen from Bt corn may dust nearby milkweeds, and monarch butterflies would die eating them. Caterpillars exposed to Bt pollen were found to have eaten less, grew more slowly and exhibited higher mortality rates Consider the problem with ecological validity in laboratory experiment: -there were higher amounts of Bt pollen on the leaves than would be found naturally (e.g. rain would diminish build up) -Larva were restricted in their diet (in the field, larva could feasibly avoid eating pollen dusted leaves)

Question 37

3.4 Explain the causes of cystic fibrosis and Huntington's disease

Answer 37

Cystic fibrosis is one of the most common genetic diseases. The recessive allele was formed by a mutation in the CFTR gene, which codes for a chloride channel in mucous membranes. The gene has been mapped on chromosome 7 and is involved in the secretion of sweat, mucus and digestive juices. Huntington's disease is a neurodegenerative disorder that usually starts to affect people between 30 and 50 years of age. It is caused by a dominant allele that has developed through the mutation of the HTT gene found on chromosome 4.

Question 38

3.5 Explain how DNA profiling is used in parental and forensic investigation.

Answer 38

from hair/blood/semen/human tissue;DNA amplified / quantities of DNA increased by PCR/polymerase chain reaction; satellite DNA/highly repetitive sequences are used/amplified; DNA cut into fragments; using restriction enzymes/restriction endonucleases; gel electrophoresis is used to separate DNA fragments; using electric field / fragments separated by size; number of repeats varies between individuals / pattern of bands is unique to the individual/ unlikely to be shared; forensic use / crime scene investigation; example of forensic use e.g. DNA obtained from the crime scene/ victim compared to DNA of suspect / other example of forensic use; paternity testing use e.g. DNA obtained from parents in paternity cases; biological father if one half of all bands in the child are found in the father; genetic screening; presence of particular bands correlates with probability of certain phenotype / allele; other example; brief description of other example;

Question 39

3.3 Define meiosis.

Answer 39

Reduction division of diploid nucleus to produce 4 haploid nuclei.

Question 40

3.4 State the genotype for all 4 types of blood.

Answer 40

Blood A: -homozygous: 1^Al^A -heterozygous: I^A i Blood B: -homozygous: |^B I^B -heterozygous: I^B i Blood AB: -ONLY heterozygous: I^A I^B Blood O: -ONLY homozygous: i

Question 41

3.4 State the gametes for sickle cell anemia alleles.

Answer 41

dominant allele (no sickle cell gene) Hb^A recessive allele (with sickle cell gene) HbAS co-dominance: Hb^A Hb^S

Question 42

3.1 Define gene Locus

Answer 42

A gene locus is the location of a gene on a chromosome. Each chromosome carries many genes.

Question 43

3.1 Describe an example of a gene with multiple alleles.

Answer 43

Nearly all genes have multiple alleles (multiple versions). For example, in humans the ABO blood type is controlled by a single gene, the isoagglutinogen gene (I for short). The I gene has three common alleles: I^A: codes for antigen type A I"B: codes for antigen type B i: codes for no antigen

Question 44

3.1 State similarities between alleles of the same gene.

Answer 44

-found at the same locus on homologous chromosomes -have mostly the same nucleotide sequence and code for the same general type of protein (for examples the A and B alleles for blood type both code for a membrane embedded protein)

Question 45

3.1 State the difference between alleles of the same gene.

Answer 45

-slightly different from each other in the sequence of nucleotides. -they can vary by just one base (i.e. A --›T), called a single nucleotide polymorphism (SNP) or by the insertion or deletion of a base.

Question 46

31 Describe a base substitution mutation.

Answer 46

A qene mutation is a change in the nucleotide sequence of a section of DNA coding for a specific trait. The new allele that results from the mutation might result in: Missense - cause one amino acid in the protein coded for by the gene to change Silent - have no effect on the protein coded for by the gene Nonsense - code for an incomplete, non- functioning polypeptide for form.

Question 47

3.1 State the size in base pairs of the human genome.

Answer 47

The human genome is composed of about 3.2 billion base pairs divided amongst nucleus chromosomes and mitochondrial DNA.

Question 48

3.1 Define "sequence" in relation to genes and/or genomes.

Answer 48

Sequence (noun): the order of the nitrogenous bases in a gene or genome. "The sequence of the gene is ATCCGTA." Sequence (verb): the process of determining the order of the nitrogenous bases in a gene of genome. "We are going to sequence the gene to test for a genetic disease"

Question 49

3.1 State the aim of the Human Genome Project.

Answer 49

The main aims of the Human Genome Project were to determine the sequence of the = 3.2 billion base pairs and identify the location of the = 20-25 thousand genes in the human genome.

Question 50

3.1 Outline the consequences of the sickle cell mutation on the impacted individual.

Answer 50

-sickle cells are destroyed rapidly in the bodies of people with the disease -causing anemia, a condition in which there aren't enough healthy red blood cells to carry adequate oxygen to the body's tissues. -anemia results in fatigue and weakness. -the sickle cells also block the flow of blood through vessels -resulting in lung tissue damage that causes acute chest syndrome, pain episodes and stroke. -it also causes damage to the spleen, kidneys and liver.

Question 51

3.1 State the number of genes in the human genome.

Answer 51

There are an estimated 20,000-25,000 genes in the human genome.

Question 52

3.1 Describe the relationship between the number of genes in a species and the species complexity in structure, physiology and/or behavior.

Answer 52

In general, eukaryotes have more genes than prokaryotes. However, within plants and animals there is little correlation between complexity and the number of genes.

Question 53

3.1 Explain which gene types are often used to assess the differences in the base sequences of a gene between two species.

Answer 53

-genes that are present in the species being studied must be selected. -for example, the COX1 gene (which codes for a protein involved in cellular respiration) is present in the majority of eukaryotic species so it is a good choice for comparing sequences between species. -additionally, the gene has been sequenced for many species and is therefor accessible in genome databases.

Question 54

3.1 Outline the use of a computer software tool to create an alignment of the gene sequences between different species.

Answer 54

-a sequence alignment is a way of arranging DNA sequences -so that similarities and differences between the sequences of different species can be identified. -computer software programs are able to complete alignments quickly and accurately.

Question 55

3.1 Outline the technological improvement that sped the DNA sequencing process.

Answer 55

-the largest advancement in gene sequencing was the automation of the process with computer- assisted technology. -what used to take humans hours or days can now be done by a computer much more rapidly, more accurately and for less money.

Question 56

3.2 Describe the structure and function of nucleoid DNA

Answer 56

In prokaryotic cells, the main DNA of the cell is collectively called the nucleoid. Unlike in eukaryotic cells, the nucleoid DNA is not enclosed in a membrane. The nucleoid DNA is a double helix that forms a circular loop and is not wrapped around histone proteins (termed "naked.")

Question 57

3.2 Compare the genetic material of prokaryotes and eukaryotes.

Answer 57

Prokaryotic DNA -Circular -One chromosome -Naked -Plasmids may be present -No intron sequences -Found in nucleoid region -One origin of DNA replication Eukaryotic DNA -Linear -Multiple chromosomes -Associated with histones -No plasmids -Intron sequences present -Contained in membrane bound nucleus -Multiple origins of DNA replication

Question 58

3.2 List similarities in the genetic material of prokaryotes and eukaryotes

Answer 58

In both prokaryotic and eukaryotic cells: -The DNA is double helix made of two anti -parallel strands of nucleotides linked by hydrogen bonding between complementary base pairs. -The replication of DNA is semi-conservative and depends on complementary base pairing. -DNA is the genetic code for creating proteins through transcription and translation.

Question 59

3.2 Describe the structure and function of plasmid DNA

Answer 59

-plasmids are extra pieces of DNA found only in prokaryotic cells. -like nucleoid DNA, plasmid DNA is circular and naked -however plasmids are much smaller than the main nucleoid DNA -plasmids replicate independently of the nucleoid DNA. -plasmids are not found in all prokaryotic cells, can be shared between bacteria and often contain genes for antibiotic resistance.

Question 60

3.2 Describe the structure of eukaryotic DNA and associated histone proteins during interphase.

Answer 60

Eukaryotic DNA is linear and associated with histone proteins in a structure called the nucleosome. During interphase, the DNA is not super-coiled into chromosomes; it is in a loose form called chromatin.

Question 61

3.2 Explain why chromatin DNA in interphase is said to look like "beads on a string.

Answer 61

The base unit of chromatin is the nucleosome, a structure composed of DNA wrapped around histone proteins. A chain of nucleosomes gives the appearance of "beads on a string."

Question 62

3.2 List three ways in which the types of chromosomes within a single cell are different.

Answer 62

Chromosomes within a cell are different in: - size (as measured by the # of base pairs) - the genes they carry - the sequence of the nitrogenous bases the location of the centromere - the banding pattern when stained

Question 63

3.2 State the number of nuclear chromosome types in a human cell.

Answer 63

There are 24 types of human chromosomes. There are 22 autosomes and 2 types of sex chromosomes

Question 64

3.2 Define homologous chromosome

Answer 64

Homologous chromosomes a chromosome pair (one from each parent), that carry the same sequence of genes but not necessarily the same alleles of those genes.

Question 65

3.2 State a similarity and a difference found between pairs of homologous chromosomes.

Answer 65

Homologous chromosomes have: -similar length -the same genes at the same locus -the majority of the same DNA base sequence -the same centromere position -will stain with the same pattern.

Question 66

3.2 Define "diploid."

Answer 66

Diploid mean that the cell contains two complete sets of the chromosomes, one chromosome originating from each parent. Diploid nuclei have pairs of homologous chromosomes

Question 67

3.2 State an advantage of being diploid.

Answer 67

-being diploid means there are two copies of each chromosome -therefore two copies of each gene that the chromosome carries. -so if one of the chromosomes carries a detrimental allele of a gene, there is a second copy of the gene -whose allele may be able to counter the effects of the mutated version. -essentially there is a "backup set of genes."

Question 68

3.2 Define haploid.

Answer 68

Haploid mean that the cell contains only one set of chromosomes; there are no homologous pairs Haploid nuclei have one chromosome of each pair

Question 69

3.2 Define "karyogram."

Answer 69

A karyogram is a micro-photograph of all chromosomes of an individual represented in a standard format.

Question 70

3.2 Outline the structure and function of the two human sex chromosomes.

Answer 70

The X chromosome is the larger of the two sex chromosomes (a length of about 156 million bp and 1805 genes) The Y chromosome is much smaller (a length of 57 million bp and about 460 genes)

Question 71

3.2 Define "autosome."

Answer 71

An autosome is any chromosome that is not a sex chromosome.

Question 72

3.2 Describe the relationship between the genome size of a species and the species complexity in structure, physiology and behavior.

Answer 72

There is a great variety of genome sizes. In general, eukaryotes have larger genomes than prokaryotes. However, the size of the genome and the number of genes do not appear to correlate to a species "complexity.

Question 73

3.2 State the minimum chromosome number in eukaryotes.

Answer 73

The minimum chromosome number in eukarvotes is 2n=2

Question 74

3.2 Explain why the typical number of chromosomes in a species is always an even number.

Answer 74

-because of sexual reproduction -in which each parent gives one set of chromosomes -resulting in an even number in the offspring.

Question 75

3.2 Explain why the chromosome number of a species does not indicate the number of genes in the species.

Answer 75

-its possible to have one large chromosome with many genes -or many smaller chromosomes with fewer genes. -likewise, it's possible to have large chromosomes with relatively few genes -smaller chromosomes that are packed full of genes -because genes refer to base sequences that would lead to the translation of proteins -genome contains non-coding sequences that makes a part of the chromosome but not genes

Question 76

3.2 Outline the advancement in knowledge gained from the development of autoradiography techniques.

Answer 76

-autoradiography is used to produce an image of a radioactive substance. -the technique is used in cellular and molecular biology to visualize structures. -for example, autoradiography can be used to visualize radioactively stained chromosomes -bands in DNA electrophoresis gels, tissue samples and single cells.

Question 77

3.3 Compare divisions of meiosis I and meiosis Il.

Answer 77

-in meiosis | there is a transition from diploid to haploid -while in meiosis II the nuclei contain only a haploid number of chromosomes. -in meiosis I chromosomes remain replicated -but in meiosis I chromatids of chromosomes are separated. -meiosis I results in two haploid cells -while meiosis Il results in four haploid cells.

Question 78

3.3 List three events that occur in other prophase 1 of meiosis.

Answer 78

1. Homologous chromosomes pair up with each other 2. A process called crossing over takes place 3. Chromatids with new combinations of alleles are produced

Question 79

3.3 Define bivalent and synapsis.

Answer 79

Bivalent: a pair of homologous chromosomes Synapsis: the fusion of chromosome pairs in prophase 1 of meiosis

Question 80

3.3 Outline the process and result of crossing over.

Answer 80

-a junction is created where one chromatid in each of the homologous chromosomes breaks -re-joins with the other chromatid. -crossing over occurs at random positions anywhere along the chromosomes. -because a crossover occurs at precisely the same position on the two chromatids involved, there is a mutual exchange of genes between the chromatids. Result: -chromatids with new combinations of alleles are produced -(because chromatids are homologous but not identical -some alleles of the exchanged genes are likely to be different)

Question 81

3.3 Describe the attachment of spindle microtubules to chromosomes during meiosis I.

Answer 81

-after the nuclear membrane has been broken down, spindle microtubules attach to the centromeres of the chromosomes. -aach chromosome is attached to one pole only (not both like in mitosis). -the two homologous chromosomes in a bivalent are attached to different poles. -the pole to which each chromosome is attached depends on which way the pair of chromosomes if facing. -this is called the orientation. -the orientation of bivalents is random, so each chromosome has an equal chance of attaching to each pole, and eventually being pulled to it. -the orientation of one bivalent does not affect other bivalents.

Question 82

3.3 Describe random orientation of chromosomes during meiosis I.

Answer 82

The orientation of bivalents is random, so each chromosome has an equal chance of attaching to each pole, and eventually being pulled to it.

Question 83

3.3 Define non- disjunction

Answer 83

The failure of homologous chromosomes to separate at anaphase.

Question 84

3.3 Describe the cause and symptoms of Down syndrome.

Answer 84

Some symptoms include hearing loss, heart and vision disorders as well as mental and growth retardation.

Question 85

3.3 DiscUss difficulties in microscopic examination of dividing cells.

Answer 85

Often no cells in meiosis are visible or the images are not clear enough to show details of the process. (Even with prepared slides made by experts it is difficult to understand the images as chromosomes form a variety of bizarre shapes during the stages of meiosis.

Question 86

3.3 Describe the discovery of meiosis.

Answer 86

From the 1880s onwards a group of German biologists carried out careful and detailed observations of dividing nuclei that gradually revealed how mitosis and meiosis occur.

Question 87

3.4 Describe conclusions from Mendel's pea plant experiments.

Answer 87

Through selective breeding of pea plants, Mendel discovered: -that certain traits show up in offspring without blending of the parent's characteristics. Mendel observed seven traits: flower color stem length seed color pod color flower position seed shape pod shape. Mendel concluded: 1. genetic "units" of inheritance are passed from parents to offspring 2. the offspring inherits one "unit" from each parent for each trait. 3. the "unit" may be masked or hidden (i.e. recessive) in an individual but can still be passed on to the next generation.

Question 88

3.4 Define gamete, haploid, and zygote.

Answer 88

A gamete is a reproductive cell, egg or sperm. Gametes are haploid; containing a single set of unpaired chromosomes. Haploid cells contain a single set of unpaired chromosomes and therefore only one allele of each gene. The zygote is the diploid cell that results from the fusion of two haploid gametes during fertilization.

Question 89

3.4 State two similarities and two differences between male and female gametes

Answer 89

Both egg and sperm are haploid (23 chromosomes in humans) cells produced through meiosis. -the egg and sperm are very different in size and shape. -eggs are large cells; sperm are much smaller. -sperm have flagella, egg do not.

Question 90

3.4 State the maximum number of alleles in a diploid zygote.

Answer 90

Alleles are variations of a single gene. Although there usually are multiple alleles for a gene in the population, any single individual can only have a maximum of two alleles of a gene, one allele on each chromosome of a homologous pair.

Question 91

3.4 Define "dominant allele." "recessive allele", and "co-dominant alleles"

Answer 91

Dominant alleles show their effect even if the individual is heterozygous, they can mask the presence of another allele. Recessive alleles only show their effect if the individual has two copies (homozygous recessive), otherwise their presence can be masked by a dominant allele. With codominant alleles, both alleles are expressed equally; there isn't masking of a recessive by a dominant allele.

Question 92

3.4 State the usual cause of one allele being dominant over another.

Answer 92

-the cause of allele dominance is complex and can vary between genes. -in general, the dominant allele codes for a functioning proteins -whereas the recessive allele codes for a less (or non-) functioning protein. -sometimes the recessive allele is the "normal" or "healthy" version of the gene.

Question 93

3.4 Define "carrier" as related to genetic diseases.

Answer 93

A genetic carrier is an individual that has inherited a recessive allele of a gene but does not display the symptoms of the disease because they also have the dominant (normal functioning) allele. Carriers are heterozygous

Question 94

3.4 Define sex linkage.

Answer 94

Sex linkage refers to genes located on the sex chromosomes, X or Y. The genes expression, inheritance pattern and effect on the phenotype will differ between males and females.

Question 95

3.4 Outline Thomas Morgan's elucidation of sex linked genes with Drosophila

Answer 95

-Thomas Hunt Morgan studied genetics of fruit flies, Drosophila. -he discovered sex-linked traits; traits that appear to associate differently in males and females. -flies normally have red eyes, but there was a mutant male with white eyes. -this white-eyed male was crossed with a red eyed female (P generation). -all offspring (Fl generation) were red-eyed therefore red is dominant over white. -then, two of the red-eyed offspring were crossed (F1 X F1). -in the offspring (F2), only males had white eyes, -suggesting that the eye-color allele is carried on the X-chromosome.

Question 96

3.4 Outline the effects of gene mutations in body cells and gamete cells.

Answer 96

-cell damage and death that result from mutations in somatic cells -occur only in the organism in which the mutation occurred -and are therefore termed somatic or non heritable effects. -cancer is the most notable long-term somatic effect. In contrast, mutations that occur in germ line cells (which become gametes, sperm and egg) -can be transmitted to future generations and are therefore called genetic or heritable effects. -genetic effects may not appear until many generations later.

Question 97

3.4 Define "mutation" as related to genetic diseases and cancer.

Answer 97

A mutation is the permanent alteration of the nucleotide sequence of the genome of an organism.

Question 98

3.4 Define "mutagen", and how it affects cells.

Answer 98

A mutagen is a chemical or physical agent that causes mutations.Mutagens cause mutations in three different ways: 1. Some are mistakenly used as bases when new DNA is synthesized at the replication fork. 2. Some react directly with DNA, causing structural changes that lead to miscopying of the template strand when the DNA is replicated. 3. Some mutagens act indirectly on DNA. They do not themselves affect DNA structure, but instead cause the cell to synthesize chemicals that have a direct mutagenic effect.

Question 99

3.4 Describe the cause and effect of red-green color blindness.

Answer 99

-red-green color blindness is caused by a sex linked recessive allele of a gene that -codes for a protein (opsin) in the eye that is sensitive to particular wavelengths of light. -the mutated allele causes red-green color vision defects.

Question 100

3.4 Describe the cause and effect of hemophilia.

Answer 100

Hemophilia is caused by a mutated allele of a gene that codes for a essential protein in the blood clotting process. Without proper clotting, hemophiliacs are prone to excessive bleeding.

Question 101

3.4 Define monohybrid, true breeding, hybrid, Fl and F2.

Answer 101

A monohybrid cross is a genetic cross between two individuals, tracking one gene of interest. True breeding organisms are those that have been bred to have a homozygous genotype The offspring of a cross between two parent organisms, "first filial." The F2 generation is the result of a cross between two F1 individuals.

Question 102

3.4 Explain the reason why the outcomes of genetic crosses do not usuallv correspond exactly with the predicted outcomes.

Answer 102

The actual outcomes of a genetic cross may not exactly match outcomes predicted based on a Punnett square because there is an element of chance in the segregation of alleles and fertilization.

Question 103

3.4 Describe the role of statistical tests in deciding whether an actual result is a close fit to a predicted result.

Answer 103

-such as the chi-square test -allow us to determine the probability of observing a discrepancy between observed (actual results) and expected (predicted results). -in other words, statistics help us determine the chance of getting the observed results given what was expected.

Question 104

3.4 Outline the conventions for constructing pedigree charts

Answer 104

A pedigree chart is a diagram that shows the occurrence of a phenotype in generations of a family. Male = square Female = circle Shaded = affected

Question 105

3.4 List three biological research methods pioneered by Mendel.

Answer 105

-large number of replicates to demonstrate reliability of results -repeats of whole experiments. -obtaining quantitative results, not only qualitative descriptions.

Question 106

3.5 Contrast sticky vs. blunt ends.

Answer 106

Blunt ends are also called non-cohesive ends, since there is no unpaired DNA strand fleeting at the end of DNA. The sticky ends, a.k.a. cohesive ends, have unpaired DNA nucleotides on either 5'- or 3'- strand, which are known as overhangs.22 Jul 2020

Question 107

3.5 Explain the function and purpose of DNA electrophoresis.

Answer 107

Electrophoresis is used to separate molecules according to their size and/or charge. -the result is a series of "bands" that each contain molecules of a particular size -the band pattern can be used to identify individuals for: -forensic analvsis -paternity testing -determining evolutionary relationships -testing for alleles associated with disease

Question 108

3.5 Describe the selectivity of the PCR.

Answer 108

A specific section of DNA can be copied using PC> By using primers that are specific to a certain sequence of nucleotides, only the targeted region will be copied

Question 109

3.5 Outline how the universality of the genetic code allows for gene transfer between species.

Answer 109

-the universal genetic code is a common language for almost all organisms -to translate nucleotide sequences of DNA and RNA to amino acid sequences of proteins. -because organisms all use the same code, a gene can be removed from one species, inserted into another and the recipient species will transcribe and translate the gene to create a functional protein.

Question 110

3.5 Define "cloning."

Answer 110

Cloning means to make an identical copy of [a DNA sequence, cell, tissue or organism].

Question 111

3.5 Outline why plasmids with genes coding for antibiotic resistance are chosen as vectors in gene transfer between species.

Answer 111

some, but not all bacteria will accept a recombinant plasmid into their cell. -How do we know which bacteria have the taken in the recombinant plasmid and which ones didn't? -by using a plasmid with a gene for antibiotic resistance, the bacteria can be grown on a growth medium that included an antibiotic. -only bacteria containing the recombinant plasmid can survive; the rest will die.

Question 112

3.5 Compare therapeutic cloning to reproductive cloning.

Answer 112

Reproductive cloning produces copies of whole animals. Therapeutic cloning produces embryonic stem cells for experiments aimed at creating tissues to replace inured or diseased tissues.

Question 113

3.5 List examole applications of gene transfer between species.

Answer 113

Human insulin protein produced by bacteria Salt-tolerant tomato plant Vitamin A produced in rice Herbicide resistance in crop plants Blood clotting factor produced in sheep milk

Question 114

3.1 Why does the proteome of a species contain a larger number of proteins than can be coded for by the genome of the same species?

Answer 114

Because there is differential and development- specific expression of genes. Some genes can code for several proteins that are expressed during the various stages of development.

Question 115

3.4 A mutation in the CFTR gene causes cystic fibrosis. Which protein does this gene code for?

Answer 115

A chloride channel in the mucous membrane; The gene is found on chromosome number 7 and codes for a protein that causes a faulty chloride channel to be embedded in cell membranes. This results in an effect on the secretion of sweat, mucus and digestive juices.

Question 116

3.3 State the importance of meiosis in the production of gametes to allow a sexual life cycle.

Answer 116

-meiosis enables a constant chromosome number to be maintained through the generations -otherwise chromosome number would double every generation

Question 117

3.3 Explain how Down syndrome could be caused by: (I) The chromosomes in a bivalent failing to separate (ii) a centromere dividing during meiosis I

Answer 117

(I) chromosomes in a bivalent should move to opposite poles in anaphase I: both chromosomes in the bivalent move to the same pole if fails to split; one cell from meiosis I has two of the pair of chromosomes and the other has none (II) one chromatid becomes separated from bivalent; the separated chromosome may move to the same pole as the intact chromosome of the two chromatids in the bivalent; centromeres should divide in meiosis Il;