Bio 3 Flashcards
3.1 Define the term
gene.
A gene is a heritable factor that consists of a
length of DNA and influences a specific
characteristic.
3.1 Outline the
relationship
between a gene
and a chromosome.
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.
3.1 Define alleles,
and outline how it is
formed.
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.
3.1 Outline the
definition of genome
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.
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
**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
3.1 Explain the
causes of sickle cell
anemial
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.
3.1 Outline the
Human Genome
Proiect and its
outcome.
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;
3.2 Distinguish
between
prokaryotic and
eukaryotic
chromosomes
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.
3.2 Describe what
homologous pairs
are in relationship
to diploid and
haploid nuclei.
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.
3.2 State why
chromosome
number and type is
a distinguishing
characteristic of a
species.
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.
3.2 Describe the
process of creating
a karyogram, and its
Uses.
-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)
3.2 Distinguish
between
heterosome and
autosomes.
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)
3.2 Describe Cairns’
technique for
measuring the
length of DNA
molecules, his
conclusion.
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.
3.2 Application:
Comparison of
genome size in T2
phage, Escherichia
coli, Drosophila
melanogaster,
Homo sapiens and
Paris japonica.
*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
3.2 Application:
Comparison of
diploid
chromosome
numbers of Homo
sapiens, Pan
troglodytes, Canis
familiaris, Oryza
sativa, Parascaris
equorum.
Homo Sapiens:
46
Pan troglodytes:
48
Canis familiaris:
78
Oryza sativa:
24
Parascaris equorum:
4
3.3 Outline the
process of meiosis.
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;
3.3 What happens
prior to meiosis?
DNA is replicated before meiosis so that all
chromosomes consist of two sister chromatids.
3.3 Explain why
meiosis is known as
reduction division?
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)
3.3 Explain how
sexual reproduction
can lead to
variation in a
species.
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.
3.3 Application:
Explain how non-
disjunction can
cause Down
syndrome and other
chromosome
abnormalities.
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.
3.3 Application:
Description of
methods used to
obtain cells for
karyotype analysis.
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.
3.4 Outline why
Mendel’s success is
attributed to his use
of pea plants.
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.
3.4 Explain the
relationship
between meiosis
and inheritance.
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)
3.4 Explain
dominant and
recessive allele in
inheritance.
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;
3.4 List out genetic
diseases that are
due to autosomal
dominant,
autosomal
recessive, Co-
dominant, and sex
linked.
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)
3.4 Describe
patterns that can be
seen regarding
diseases caused by
autosomal
dominant,
autosomal
recessive, and sex
linked.
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
3.4 Explain the
rarity of genetic
diseases
-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.
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.
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
3.5 Explain how gel
electrophoresis and
polymerase chain
reaction are used in
DNA profiling.
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.
3.5 Explain how
gene modification is
carried out.
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.
- The recombinant construct (including the gene
of interest) is finally introduced into an
appropriate host cell or organism - Transgenic cells, once isolated and purified, will
hopefully begin expressing the desired trait
encoded by the gene of interest.
3.5 Define what
clones are, and the
production of
cloned embryos.
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.
3.5 Describe some
natural methods of
cloning.
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
3.5 Describe and
explain the two
methods of cloning
in animals.
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)
3.5 Design of an
experiment to
assess one factor
affecting the
rooting of stem-
cuttings.
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)
3.5 Assessment of
the potential risks
and benefits
associated with
genetic
modification of
crops.
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.
3.5 Analysis of data
on risks to monarch
butterflies of Bt
crops.
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)
3.4 Explain the
causes of cystic
fibrosis and
Huntington’s
disease
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.
3.5 Explain how
DNA profiling is
used in parental and
forensic
investigation.
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;
3.3 Define meiosis.
Reduction division of diploid nucleus to produce
4 haploid nuclei.
3.4 State the
genotype for all 4
types of blood.
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
3.4 State the
gametes for sickle
cell anemia alleles.
dominant allele (no sickle cell gene)
Hb^A
recessive allele (with sickle cell gene)
HbAS
co-dominance:
Hb^A Hb^S
3.1 Define gene
Locus
A gene locus is the location of a gene on a
chromosome. Each chromosome carries many
genes.
3.1 Describe an
example of a gene
with multiple alleles.
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
3.1 State similarities
between alleles of
the same gene.
-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)
3.1 State the
difference between
alleles of the same
gene.
-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.
31 Describe a base
substitution
mutation.
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.
