Topic 3 - Genetics Flashcards
(174 cards)
1
Q
Define “gene”.
A
A gene is a sequence of DNA nucleotides that codes for an RNA or protein that in turn influences a trait/characteristic.
2
Q
Define “gene locus.”
A
A gene locus is the location of a gene on a chromosome. Each chromosome carries many genes.
3
Q
Define “allele.”
A
An allele is a version/variation of a gene. Most genes come in a variety of different forms.
For analogy: if there is an ice cream gene , then the alleles would be vanilla, chocolate and mint.
4
Q
Describe an example of a gene with multiple alleles.
A
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
5
Q
State similarities between alleles of the same gene.
A
Alleles of the same gene are 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).
6
Q
State the difference between alleles of the same gene.
A
Alleles of the same gene are 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.
7
Q
State the source of new alleles of a gene.
A
New alleles (versions) of a gene are formed through random mutation (changes) in the DNA sequence of the gene. Most new mutations arise due to errors in DNA replication.
8
Q
Describe a base substitution mutation.
A
Substitution mutations replace one base with another. 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.
9
Q
Define “genome.”
A
The genome is the complete set of genes and genetic material present in a cell or organism.
10
Q
State the size in base pairs of the human genome.
A
The human genome is composed of about 3.2 billion base pairs divided amongst nucleus chromosomes and mitochondrial DNA.
11
Q
Define “sequence” in relation to genes and/or genomes.
A
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.”
12
Q
State the aim of the Human Genome Project.
A
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.
13
Q
Outline outcomes of the Human Genome Project.
A
The Human Genome Project:
-determined the sequence of the base pairs in the sample humans
- identified the location of many genes on chromosomes
- identified human genetic variations (SNPs)
-improved detection of genetic diseases
-developed new technologies, medical treatments and research techniques
-spurred international collaboration
14
Q
Define “sickle cell anemia.”
A
Sickle cell anemia is a group of disorders that affects hemoglobin, the molecule in red blood cells that delivers oxygen to cells throughout the body. People with this disorder have atypical hemoglobin molecules, which distort red blood cells into a sickle, or crescent, shape.
15
Q
Define “substitution mutation.”
A
A substitution is a mutation that exchanges one base for another (i.e., switching an A to a C). Such a substitution could: change a codon to one that encodes a different amino acid and cause a change in the protein produced.
16
Q
State the cause of sickle cell anemia, including the name of differences in the Hb alleles.
A
Sickle cell anemia is caused by single base substitution mutation in the gene coding for one of the polypeptide chains in hemoglobin. In the mutation, the sequence GAG (on the sense strand of DNA) is mutated to GTG. This results in a codon that codes for the amino acid VAL instead of GLU.
17
Q
Outline the consequences of the sickle cell mutation on the impacted individual.
A
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.
18
Q
Explain the consequence of the mutation causing sickle-cell anemia in relation to the processes of transcription and translation.
A
With sickle cell, the sequence GAG (on the sense strand of DNA) is mutated to GTG. When the mutated sickle cell gene is transcribed, the mRNA codon becomes GUG rather than GAG. During translation, the mutated codon will code for the wrong amino acid to join the polypeptide (where there should be a glutamic acid a valine is inserted instead). As a result, the polypeptide will fold into an incorrect shape, resulting in a distorted hemoglobin molecule that in turn alters the red blood cell shape and reduces its ability to carry oxygen.
19
Q
State the number of genes in the human genome.
A
There are an estimated 20,000-25,000 genes in the human genome.
20
Q
Describe the relationship between the number of genes in a species and the species complexity in structure, physiology and/or behavior.
A
In general, eukaryotes have more genes than prokaryotes. However, within plants and animals there is little correlation between complexity and the number of genes.
21
Q
Explain which gene types are often used to assess the differences in the base sequences of a gene between two species.
A
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.
22
Q
Outline the use of a computer software tool to create an alignment of the gene sequences between different species.
A
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.
23
Q
Summarize the information that can be determined given gene sequence alignment data.
A
Sequence alignment data can be used to measure evolutionary relationships between species. The more similar two sequences, the more closely related two species are.
24
Q
Outline the technological improvement that sped the DNA sequencing process.
A
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.
25
Describe the structure and function of nucleoid DNA.
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.")
26
List differences in the genetic material of prokaryotes and eukaryotes.
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
27
Define the term "naked" in relation to prokaryotic DNA.
Naked means that the DNA does not wrap around histone proteins.
28
List similarities in the genetic material of prokaryotes and eukaryotes.
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.
29
Describe the structure and function of plasmid DNA.
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 and 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.
30
Describe the structure of eukaryotic DNA and associated histone proteins during interphase.
Eukaryotic DNA is linear and associate 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.
31
Explain why chromatin DNA in interphase is said to look like "beads on a string."
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."
32
List ways in which the types of chromosomes within a single cell are different.
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
33
State the number of nuclear chromosome types in humans.
There are 24 types of human chromosomes. There are 22 autosomes and 2 types of sex chromosomes.
34
Define "homologous chromosome."
Homologous chromosomes a chromosome pair (one from each parent).
35
State a similarity between pairs of homologous chromosomes.
Homologous chromosomes have similar length, the same genes at the same locus, the majority of the same DNA base sequence, the same centromere position and will stain with the same pattern.
36
State a difference between pairs of homologous chromosomes.
The genes and the position of the genes on each homologous chromosome are the same, however the genes may be different alleles (therefor slight differences in sequence of the gene).
37
Define "diploid."
Diploid mean that the cell contains two complete sets of the chromosomes, one chromosome originating from each parent.
38
State the human cell diploid number.
Somatic human cells have a diploid number of
2n=46
Where
2: there are two of each of the...
n: number of chromosome types
=: for a total of
46= the number of chromosomes
39
Outline the formation of a diploid cell from two haploid gametes.
Gametes (egg and sperm) are haploid. When gametes fuse during fertilization, the two sets of chromosomes (one from the egg and one from the sperm) combine to create a diploid zygote.
40
State an advantage of being diploid.
Being diploid means there are two copies of each chromosome, and 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."
41
Define "haploid."
Haploid mean that the cell contains only one set of chromosomes; there are no homologous pairs.
42
State the human cell haploid number.
n=23
Where
n: the number of chromosome types
=: equals
23
43
List example haploid cells.
The eggs and sperm of humans are haploid.
44
State why chromosome number and type is a distinguishing characteristic of a species.
Organisms with differing numbers of chromosomes are usually not able to interbreed, maintaining the same number of chromosomes with the species.
45
Define "karyogram."
A karyogram is a micro-photograph of all chromosomes of an individual represented in a standard format.
46
Describe the process of creating a karyogram.
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. A photograph of the chromosomes is taken. The images of the chromosomes are then organized in a standard pattern.
47
List the characteristics by which chromosomes are arranged on the karyogram.
Images of the chromosomes are arranged by size (largest to smallest, sex chromosomes always last) and paired based on banding pattern and centromere position.
48
Outline the procurement of fetal cells from which chromosomes are isolated for arrangement on a karyogram.
Karyotyping requires cells that are in metaphases, so the chromosomes are condensed and visible in the cells. In prenatal testing, fetal cells can be collected from chorionic villus sampling or by amniocentesis.
49
List applications of karyogram analysis (karyotyping).
Karyotypes are used to prenatally identify the sex of the fetus and/or abnormal chromosome numbers (for example Down syndrome due to extra chromosome 21).
The results of a karyogram analysis may lead to a decision to abort the fetus or to prepare for consequences of abnormality in offspring.
50
Outline the structure and function of the two human sex chromosomes.
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)
51
Define "autosome."
An autosome is any chromosome that is not a sex chromosome.
52
Define "sex chromosome."
A sex chromosome is a chromosome involved with determining the sex of an organism, typically one of two kinds, X or Y in humans.
53
Outline sex determination by sex chromosomes.
Biological sex is usually determined by which sex chromosomes are present.
XX = female
XY = male
The male parent determines the sex of the offspring by either passing on an X chromosome (to produce a female offspring) or a Y chromosome (to produce a male offspring).
54
Outline conclusions drawn from the images produced using Cairn's autoradiography technique.
Cairn's was able to see that prokaryotic chromosomes are circular and measuring lengths of chromosomes.
He also observed the DNA replication fork.
55
Describe Cairn's technique for producing images of DNA molecules from E. coli.
Cairn's radioactively labeled DNA to produce images of the molecule. This allows him to visualized and measure the length of DNA molecules.
56
Describe the relationship between the genome size of a species and the species complexity in structure, physiology and behavior.
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."
57
State the minimum chromosome number in eukaryotes.
The minimum chromosome number in eukaryotes is 2n=2
58
Explain why the typical number of chromosomes in a species is always an even number.
The reason why most eukaryotic organisms have an even number of chromosomes is because of sexual reproduction, in which each parent gives one set of chromosomes, resulting in an even number in the offspring.
59
Explain why the chromosome number of a species does not indicate the number of genes in the species.
The number of chromosomes does not indicate the number of genes. It's 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 or smaller chromosomes that are packed full of genes!
60
Deduce the sex of an individual given a karyogram [female].
To determine sex from a karyogram, examine the last pair of chromosomes.
XX= female
61
Deduce the sex of an individual given a karyogram [male].
To determine sex from a karyogram, examine the last pair of chromosomes.
XY= male
62
Describe the use of a karyogram to diagnose Down syndrome.
Down Syndrome is caused by a nondisjunction of chromosome #21, resulting in three chromosome #21, which can be observed in a karyogram.
63
Explain the benefit of a publicly accessible genome database.
Effort has been made to make human genome sequence information freely
accessible to researchers around the globe. Data obtained from Human Genome Project funded research must be publicly available. The rationale is that our ability to expeditiously and effectively increase our knowledge of genetics
depends on the ability of researchers to access current information.
64
Outline how to search an online database [BLAST] for a given gene.
BLAST (Basic Local Alignment Search Tool) is to the nucleotide or protein sequence database as a search engine is to the internet. BLAST is a sequence alignment tool that allows you to identify an unknown sequence, map a sequence in a genome or get clues about related sequences.
Using BLAST is like doing an experiment; you must optimize the experimental conditions to get good results. Too wide a search can take a long time and give you many random and meaningless matches. Too narrow a search will possibly miss significant matches.
65
Outline the advancement in knowledge gained from the development of autoradiography techniques.
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.
66
Define "meiosis."
Meiosis is a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes.
67
Compare divisions of meiosis I and meiosis II.
Meiosis I
Reductive division (diploid to haploid)
Results in two haploid cells
Chromosomes remain replicated (X)
Crossing over occurs
Proceeded by interphase with DNA replication
Meiosis II
Non-reductive division (haploid to haploid)
Results in four haploid cells
Chromatids of a chromosome separate (X to / and \)
No crossing over occurs
Proceeded by interkinesis, without DNA replication
68
Compare sexual and asexual life cycles.
The life cycle is the period of time that an organism passes through until producing offspring of its own.
Sexual
Two parents
Meisosis
results in increased genetic variation
Asexual
One parent
Fission, mitosis or budding
Requires less energy
69
Explain why meiosis must occur as part of a sexual life cycle.
The sexual life cycle combines genetic information from two parents. In order to maintain the correct number of chromosomes in the offspring, the parents must undergo meiosis to create gametes with half of the genetic information.
70
State that DNA is replicated in interphase before meiosis.
During "S" phase of interphase, before meiosis, the DNA molecule(s) in the cell replicate, creating two identical copies of the DNA, held together at a centromere.
71
Define "chromatid."
A chromatid is one-half of two identical strands of DNA within a replicated chromosome. During cell division, the two identical chromatids are joined at the region called the centromere.
72
Outline the movement and structure of DNA through the stages of meiosis.
G1 of interphase: single, unreplicated, non-super-coiled chromatin DNA
S of interphase: DNA replication results in a two identical copies of DNA connected a the centromere, still not super-coiled
Prophase 1: replicated DNA begins to super-coil into chromosomes. Homologous chromosomes pair.
Metaphase 1:
Homologous pairs of replicated chromosomes move to the cell equator.
Anaphase 1: homologous pairs of replicated chromosomes separate and move to opposite poles of the cell.
Telophase 1: DNA may de-condense from supercoiled chromosome form, but is still replicated with sister chromatids.
Prophase 2: replicated DNA again super-coils into chromosomes.
Metaphase 2:
Replicated chromosomes move to the cell equator. No pairing of chromosomes!
Anaphase 2: sister chromatids separate and move to opposite poles of the cell.
Telophase 2: the DNA de-condenses and returns to chromatin form.
73
List three events that occur in prophase 1 of meiosis.
1. Pairing of homologous chromosomes
2. Crossing over
3. Condensation
74
Define "bivalent."
A bivalent is a pair of homologous chromosomes physically attached at a chiasma during prophase 1.
75
Define "synapsis."
The process of the pairing of homologous chromosomes during prophase 1.
76
Define "chiasma."
The point at which paired chromosomes remain in contact during the first phase of meiosis, and at which crossing over and exchange of genetic material occur between the strands.
77
Outline the process and result of crossing over.
During prophase 1 of meiosis, homologous chromosomes exchange pieces of non-sister chromatids. This results in new combinations of genes, creating "recombinant chromosomes." Crossing over occurs at a location on the chromosome called the chiasma.
78
Define "condensation" in relation to meiosis.
Condensation refers to the process of compacting DNA molecules, often by super-coiling chromatin to form chromosomes.
79
Describe the attachment of spindle microtubules to chromosomes during meiosis I.
Spindle microtubules are long protein fibers that attach chromosomes to the poles of the cell. In meiosis 1, the homologous chromosomes are each attached to a different pole of the cell. The way the pairs align within the pair, and therefore the pole to which each chromosome is attached, is random.
80
Describe random orientation of chromosomes during meiosis I.
The way the chromosomes of a homologous pair orient at the metaphase plate during meiosis 1 is random; this means that the maternal or paternal chromosome are equally likely to move to either pole of the cell. This also means that the orientation of one homologous pair does not affect the orientation of any of the other homologous pairs.
81
Explain why meiosis I is a reductive division.
Meiosis 1 is considered a reductive division because the chromosome number begins as diploid (2 of each chromosome type) and at the end of meiosis 1 the chromosome number is haploid (1 of each chromosome type). The chromosome number is reduced.
82
State that cells are haploid at the end of meiosis I.
At the end of meiosis 1 the chromosome number is haploid (1 of each chromosome type).
83
Define "genetic variation."
Genetic variation is a term used to describe the variation (differences) in the DNA sequences in each of our genomes.
84
State the the number of chromosome combinations possible due to random orientation is 2^n.
The number of possible chromosome combinations in a gamete due to the random orientation of chromosomes during metaphase 1 of meiosis is 2^n, where n= the haploid number of chromosomes.
85
Explain how crossing over promotes genetic variation.
During prophase 1 of meiosis, homologous chromosomes exchange pieces of non-sister chromatids. This results in new combinations of genes which is a sources of genetic variation in the population.
86
Explain how random orientation of homologous chromosomes during meiosis promotes genetic variation.
During metaphase 1 of meiosis, each homologous pair of chromosomes is positioned independently of the other pairs Therefore, the first meiotic division results in a random combination of maternal and paternal chromosomes into daughter cells, which is a sources of genetic variation in the population.
87
Outline the role of fertilization as a source of genetic variation.
Fertilization is the fusion of gametes to form a zygote with a unique combination of alleles from each parent.
88
Define non-disjunction.
Non-disjunction is the failure of a pair of homologous chromosomes (in anaphase 1) or sister chromatids (in anaphase 2) to separate normally during meiosis or mitosis.
89
State the result of non-disjunction.
Non-disjunction results in an abnormal number of chromosomes in the daughter cells.
90
Describe the cause of Down syndrome.
Down syndrome is most often caused by trisomy 21, a condition where there is an extra chromosome 21. The extra chromosome is the result of non-disjunction during meiosis, which leaves a sperm or egg cell with an extra chromosome.
91
Explain the relationship between parental age and chances of non-disjunction.
The age of the parent (usually mom) is positively associated with the chance of a non-disjunction event.
92
Describe amniocentesis as a procedure for obtaining fetal cells for production of a karyotype.
In amniocentesis, a needle is inserted through the abdomen into the uterus. Amniotic fluid is withdrawn, which contains cells from the fetus that can be used in karyotyping. A risk is premature uterine contractions.
93
Describe chorionic villus sampling as a procedure for obtaining fetal cells for production of a karyotype.
In chorionic villus sampling, a thin tube is inserted into the uterus via the vagina. A small sample of placenta is removed, which contains fetal cells that can be used in karyotyping. A risk is bleeding.
94
Draw a diagram of a cell in prophase 1 of meiosis.
Replicated chromatin condenses into chromosome.
Homologous chromosomes pair up (synapsis) to form a bivalent.
Crossing over between homologous, non-sister chromatids.
95
Draw a diagram of a cell in metaphase 1 of meiosis.
Homologous pairs of chromosomes (bivalents) line up at the metaphase plate.
96
Draw a diagram of a cell in anaphase 1 of meiosis.
Homologous chromosomes are pulled to opposite poles of the cell.
97
Draw a diagram of a cell in telophase 1 of meiosis.
The nuclear membrane may reform around the now haploid chromosomes and the chromosomes decondense. Cytokinesis occurs simultaneously, forming two cells.
98
Draw a diagram of a cell in prophase 2 of meiosis.
The nuclear membrane breaks does and DNA condenses to chromosome form. The spindle fibers form.
99
Draw a diagram of a cell in metaphase 2 of meiosis.
The replicated chromosomes are moved to the metaphase plate. Since the cell is haploid in meiosis 2, it is impossible for homologous chromosomes to pair.
100
Draw a diagram of a cell in anaphase 2 of meiosis.
Sister chromatids of the replicated chromosome are pulled towards opposite poles of the cell.
101
Draw a diagram of a cell in telophase 2 of meiosis.
The nuclear membrane forms around each set of chromosomes and the chromosomes decondense. Cytokinesis occurs simultaneously to create four haploid cells from the single original cell that began meiosis.
102
Discuss difficulties of microscopic examination of dividing cells.
In early microscopic examination of cells, the cells had to be preserved before viewing. This killed the cells and prevented processes like meiosis from being observed in action. Additionally, it wasn't until DNA stains were discovered that the behavior of chromosomes during meiosis could be observed.
103
Outline the discovery of meiosis.
Hertwig (1876) observed one cell dividing to create four cells, making sea urchin eggs.
Van Beneden (1883) discovered how chromosomes move during meiosis by studying roundworms.
Weismann (1890) theorized how the meiotic divisions could lead to daughter cells with only half of the genetic information.
104
Describe conclusions drawn from Mendel's pea plant experiments.
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 and 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.
105
Define "gamete."
A gamete is a reproductive cell, egg or sperm. Gametes are haploid; containing a single set of unpaired chromosomes.
106
Define "haploid."
Haploid cells contain a single set of unpaired chromosomes and therefore only one allele of each gene.
107
Define "zygote."
The zygote is the diploid cell that results from the fusion of two haploid gametes during fertilization.
108
State two similarities and two differences between male and female gametes.
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.
109
State the outcome of allele segregation during meiosis.
Mendel's Law of Segregation states that a pair of alleles (variations of the same gene) separate into different gamete cells during meiosis.
110
Outline the possible combination of alleles in a diploid zygote for a gene with two alleles.
For a gene with two alleles, the zygote could be either:
homozygous dominant: two copies of the dominant allele (i.e. AA)
heterozygous: one copy of the dominant allele and one copy of the recessive allele (i.e. Aa)
homozygous recessive: two copies of the recessive allele (i.e. aa)
111
Outline the possible combination of alleles in a diploid zygote for a gene with three alleles.
Many genes have multiple alleles within the population. For example, in ABO blood typing there are three common alleles for the Isoagglutinogen gene: I^A, I^B and i.
Within a diploid individual there may only be a combination of two of the alleles:
I^A, I^A (type A)
I^A, I^B (type AB)
I^A, i (type A)
I^B, I^B (type B)
I^B, i (type B)
i, i (type O)
112
State the maximum number of alleles in a diploid zygote.
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.
113
Define "dominant allele."
Different versions of a gene are called alleles. Dominant alleles show their effect even if the individual is heterozygous, they can mask the presence of another allele.
114
Define "recessive allele."
Different versions of a gene are called alleles. Recessive alleles only show their effect if the individual has two copies (homozygous recessive), otherwise their presence can be masked by a dominant allele.
115
State the usual cause of one allele being dominant over another.
The cause of allele dominance is complex and can vary between genes. However, 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.
116
Define "codominant alleles."
With codominant alleles, both alleles are expressed equally; there isn't masking of a recessive by a dominant allele.
117
Using the correct notation, outline an example of codominant alleles.
Since there isn't a true dominant allele, a lowercase letter is NOT used when alleles are codominant. Rather, two different capital letters are used and places as superscript next to a common letter that represents the name of the gene. For example, type A and type B alleles of the Isoagglutinogen gene.
I^A and I^B are codominant.
118
Define "carrier" as related to genetic diseases.
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.
119
Explain why genetic diseases are rare and usually appear unexpectedly in a population.
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.
120
Describe why it is not possible to be a carrier of a disease caused by a dominant allele.
A carrier is an individual with a heterozygous genotype, carrying the disease allele but not showing the disease phenotype. If the disease is due to a dominant allele, the individual will show the disease phenotype when heterozygous.
121
Outline inheritance patterns of genetic diseases caused by dominant alleles.
In the case of a disease caused by a dominant allele, only one copy of the disease allele is needed for the individual to express the disease phenotype.
If a parent is homozygous dominant, there is a 100% chance the offspring will inherit the allele and express the genetic disease.
If a parent is heterozygous, there is a 50% chance the offspring will inherit the allele.
All affected individuals will have at least one parent with the disease.
122
Explain sickle cell anemia as an example of a genetic disease caused by codominant alleles.
Sickle cells anemia is a rare disease where red blood cells become thin and elongated. If a person has one copy of the sickle cell allele, half of their red blood cells will be misshapen. The alleles are codominant since both normal and sickle cell shapes are seen in a heterozygous individual.
123
Define "sex linkage."
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.
124
Outline Thomas Hunt Morgan's discovery of sex linked genes with Drosophila.
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 (F1 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.
125
Summarize the correct notation for sex linked genes.
With sex linked traits, the X and Y chromosome are shown with symbols for the dominant and recessive alleles written as superscripts next to the chromosome.
126
Describe the pattern of inheritance for sex linked genes.
Genes that are located on just one of the sex chromosomes are sex-linked. Common examples are colorblindness and hemophilia.
Because males only have one X-chromosome, genes on the X are expressed in the male phenotype. If the male has a recessive allele for an X-linked gene, it will be expressed because there isn't a second X chromosome with another allele that could mask the recessive allele. As a result, sex-linked conditions tend to be more commonly expressed in males.
Females can be homozygous or heterozygous for a sex-linked condition. In heterozygous females, a recessive allele on the X chromosome can be masked by a dominant allele on the other X chromosome. Heterozygous females are called "carriers" because they carry the allele but do not express the condition.
127
Construct Punnett grids for sex linked crosses to predict the offspring genotype and phenotype ratios.
1. Create a key to the alleles using correct notation (XY with superscript alleles on the X)
2. Draw a 2 x 2 square
3. Label the rows with one parent's genotype, using the notation for sex linked genes
4. Label the columns with the other parent's genotype, using the notation for sex linked genes
5. Have each box "inherit" alleles from its row and column.
6. Interpret the Punnett square, summarizing the percent of males and females with each phenotype.
128
List example genetic diseases with their inheritance pattern.
Cystic fibrosis - autosomal recessive
Stargardt's disease - autosomal recessive
Hemophilia - sex linked recessive
Huntington's disease - autosomal dominant
Phenylketonuria (PKU) - autosomal recessive
Red-green color blindness - sex linked recessive
129
Explain why most genetic diseases are rare in a population.
Most genetic diseases are caused by alleles that are rare in the population. In the case of an autosomal recessive disease, a person must inherit two copies of a rare allele (one from each parent).
130
Outline the effect of radiation on the structure of DNA.
UV and ionizing radiation alters chemical bonds and may result in a change to the DNA sequence. The mutation is a random process.
Cancer is produced if radiation does not kill the cell but creates an error in the DNA blueprint that contributes to eventual loss of control of cell division, and the cell begins dividing uncontrollably. This effect might not appear for many years.
131
Outline the effects of gene mutations in body cells and gamete cells.
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.
132
Define "mutation" as related to genetic diseases and cancer.
A mutation is the permanent alteration of the nucleotide sequence of the genome of an organism.
133
Define "mutagen."
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.
134
Describe inheritance of ABO blood types.
The ABO blood groups are determined by the Isoagglutinogen gene. The gene codes for an enzyme protein that modifies the carbohydrate molecule attached to a protein on the surface of red blood cells. The I gene has three alleles: I^A, I^B and i.
Alleles I^A and I^B are completely dominant over allele i. So:
I^A, i (type A)
I^B, i (type B)
Alleles I^A and I^B are codominant, so bother are expressed in a heterozygous individual: I^A, I^B (type AB)
135
Describe the cause and effect of red-green color blindness.
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.
136
Explain inheritance patterns of red-green color blindness.
Red-green color blindness is X-linked recessive.
X-linked: the gene is located on the X chromosome
Recessive: to be colorblind, males only need one mutated allele, females need two mutated alleles
137
Describe the cause and effect of hemophilia.
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.
138
Explain inheritance patterns of hemophilia.
Hemophilia is X-linked recessive.
X-linked: the gene is located on the X chromosome
Recessive: to be hemophiliac, males only need one mutated allele, females need two mutated alleles (which is exceedingly rare)
139
Outline the inheritance pattern of cystic fibrosis.
Cystic fibrosis is autosomal recessive.
Autosomal: the gene is located on an autosome, NOT a sex chromosome
Recessive: to have CF, males and females need to inherit two mutated alleles (one from each parent)
140
Outline the inheritance pattern of Huntington's disease.
Huntington's disease is autosomal dominant.
Autosomal: the gene is located on an autosome, NOT a sex chromosome
Dominant: to have Huntington's, males and females only need to inherit one mutated allele.
141
Outline the effects of radiation exposure after nuclear exposure at Hiroshima.
Hiroshima was the site of an atomic bomb at the end of WWII (1945). Thousands of people died instantly and many others suffered effects of radiation poisoning (hair loss, bleeding, vomiting and diarrhea).
142
Outline the effects of radiation exposure after nuclear exposure at Chernobyl.
There was an accidental explosion at the Chernobyl nuclear power plant in the USSR (1986). Many people died or developed cancer as a result of the radiation exposure.
143
Define "monohybrid."
A monohybrid cross is a genetic cross between two individuals, tracking one gene of interest.
144
Define "true breeding."
True breeding organisms are those that have been bred to have a homozygous genotype.
145
Define "F1" as related to genetic crosses.
The offspring of a cross between two parent organisms, "first filial."
146
Define "F2" as related to genetic crosses.
The F2 generation is the result of a cross between two F1 individuals.
147
Explain how to determine possible alleles present in gametes given parent genotypes.
The parent genotype consists of two alleles. During meiosis, these alleles segregate into gametes with equal probability.
148
Construct Punnett grids for single gene crosses to predict the offspring genotype and phenotype ratios.
1. Create a key for the allele identification
2. Draw a 2 x 2 square
3. Label the rows with one parent's possible alleles in the gametes
4. Label the columns with the other parent's possible alleles in the gametes
5. Have each box "inherit" alleles from its row and column.
6. Interpret the Punnett square, summarizing the percent offspring with each phenotype.
149
Using a Punnett grid, deduce the probability of a child inheriting an autosomal recessive disease, if both of the parents are carriers of the disease but do not have the disease themselves..
1. Create a key for the allele identification (S dominant; s recessive)
2. Draw a 2 x 2 square
3. Label the rows with one parent's possible alleles in the gametes (Ss)
4. Label the columns with the other parent's possible alleles in the gametes (Ss)
5. Have each box "inherit" alleles from its row and column.
6. Interpret the Punnett square, summarizing the percent offspring with each phenotype (3 normal : 1 with disease)
150
Explain the reason why the outcomes of genetic crosses do not usually correspond exactly with the predicted outcomes.
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.
151
Describe the role of statistical tests in deciding whether an actual result is a close fit to a predicted result.
Statistics, 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.
152
Outline the conventions for constructing pedigree charts.
A pedigree chart is a diagram that shows the occurrence of a phenotype in generations of a family.
Male = square
Female = circle
Shaded = affected
153
Explain how to deduce an autosomal dominant inheritance pattern in a pedigree chart.
Autosomal Dominant
Appear equally in males and female
Does not skip generations
Affected offspring have an affected parent
154
Explain how to deduce an autosomal recessive inheritance pattern in a pedigree chart.
Autosomal Recessive
Appear equally in males and female
Can skip generations
155
Explain how to deduce an X-linked recessive inheritance pattern in a pedigree chart.
X-linked Recessive
Appear much more frequently in males
Can skip generations
Mothers of affected sons are carriers
156
Outline why Mendel's success is attributed to his use of pea plants.
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).
157
List biological research methods pioneered by Mendel.
Large number of replicates to demonstrate reliability of results.
Repeats of whole experiments.
Obtaining quantitative results, not only qualitative descriptions.
158
Describe the role of restriction enzymes in biotechnology applications.
Restriction enzymes cut DNA at specific base sequences.
159
Explain the function and purpose of DNA electrophoresis.
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 analysis
-paternity testing
-determining evolutionary relationships
-testing for alleles associated with disease
160
Describe how and why DNA fragments separate during electrophoresis.
DNA is loaded into the well of an agarose gel. Because DNA is negatively charged (due to the phosphate groups) it will be pulled through the gel by an electric field. DNA fragments move towards the positive electrodes, with smaller fragments moving further.
161
State the function of the PCR.
The Polymerase Chain Reaction is used to make many copies ("amplify") of a specific region of DNA, making millions of copies of a particular DNA sequence.
162
Describe the selectivity of the PCR.
A specific section of DNA can be copied using PCR> By using primers that are specific to a certain sequence of nucleotides, only the targeted region will be copied.
163
Outline the process of DNA profiling.
1. A sample of DNA/blood/saliva/semn is obtained
2. A comparison or reference sample of DNA is also obtained
3. PCR is used to produce more copies of the DNA
4. DNA is cut into fragments by restriction enzymes
5. DNA fragments are separated by size via electrophoresis to form a series of bands
6. bands are compared between the different samples
7. If the banding pattern is the same, then the DNA is from the same source. Children will share bands with either 1 or both parents.
164
Outline how the universality of the genetic code allows for gene transfer between species.
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.
165
Contrast sexual and asexual reproduction.
Asexual reproduction generates offspring that are genetically identical to a single parent. In sexual reproduction, two parents contribute genetic information to produce genetically unique offspring.
166
Define "clone."
A clone is an organism or cell, or group of organisms or cells, produced asexually from one ancestor, to which they are genetically identical.
167
Define "cloning."
Cloning means to make an identical copy of [a DNA sequence, cell, tissue or organism].
168
Outline an example of natural cloning in plants.
Some plants produce clones naturally by asexual reproduction. For example:
Spider plants grow new plants, called plantlets, on their stems
Potato plants produce tubers, which can grow new roots and shoots
Strawberry plants grow stems called runners, which have plantlets on them
169
Outline an example of natural cloning in animals.
Natural clones, identical twins, occur in humans and other mammals. These twins are produced when a zygote splits, creating two or more embryos that carry almost identical DNA. Identical twins have nearly the same genetic makeup as each other, but they are genetically different from either parent.
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.
170
Describe the process of cloning via somatic cell nuclear transfer.
Somatic cell nuclear transfer is a technique for cloning. The nucleus is removed from a healthy egg. This egg becomes the host for a nucleus that is transplanted from another cell, such as a skin cell. The resulting embryo can be used to generate embryonic stem cells with a genetic match to the nucleus donor (therapeutic cloning), or can be implanted into a surrogate mother to create a cloned individual, such as Dolly the sheep (reproductive cloning).
171
List example sources of DNA that can be used in DNA profiling.
DNA can be obtained from:
-blood
-semen
-saliva
-tissue samples
172
Describe a technique for genetic modification including plasmids, restriction enzymes and ligase.
Gene transfer takes a gene from one organism and inserts it into another.
1. Plasmid removed from bacteria;
2. Plasmid cleaved/cut open by restriction enzymes;
3. The same a restriction enzyme then cuts out a target gene of interest (i.e. the insulin gene) from a chromosome;
4. The plasmid and target DNA are mixed; the sticky ends of the plasmid and target gene of interest will bond at their complementary base sequences;
5. DNA ligase is used to bond the target gene into the plasmid, forming a recombinant plasmid.
6. The recombinant plasmid is inserted into a host cell bacterium.
7. The bacteria with the recombinant plasmid multiply and produce a tiny amount of the protein product (i.e. insulin) from the gene of interest.
173
Outline why plasmids with genes coding for antibiotic resistance are chosen as vectors in gene transfer between species.
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.
174
List example applications of gene transfer between species.
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
