Lecture Flashcards
1
Q
What is a gene?
A
A fundamental unit of heredity, helps determine characteristics.
2
Q
What is an allele?
A
Alleles are multiple forms of a gene.
3
Q
What is the basic function of DNA?
A
DNA carries genetic information.
4
Q
Every allele has a specific ______ on a chromosome.
A
Every allele has a specific locus on a chromosome.
5
Q
What is the principle of segregation?
A
Homologous chromosomes segregate in Metaphase 1.
Diploid becomes haploid.
6
Q
Give a brief overview of every step of mitosis.
A
(lecture 1&2)
7
Q
What is the principle of independent assortment?
A
Chromosomes separate independently of one another. This increases genetic variability.
(dihybrid cross give 9:3:3:1)
8
Q
What is an assumption made when discussing pedigrees?
A
If the trait is rare and autosomal recessive, then individuals who marry/mate into the pedigree are homozygous for the normal allele unless there is evidence to the contrary.
9
Q
What are some types of recessive mutations? What is their flaw?
A
Null/ Amorphic allele:
- non functional protein produced
- no protein produced
Hypomorphic allele:
- poorly functioning protein produced
- reduced amount of normally functioning protein produced
10
Q
What are some types of dominant mutations? What is their flaw?
A
Hypermorphic mutations:
- overproduction of normal protein
- production of protein with increased activity levels
Neomorphic allele:
- presence of altered protein with new function
- altered protein interferes with wild type allele (called dominant negative allele”)
11
Q
What is the difference between the multiplication rule and the addition rule?
A
Multiplication rule: this AND that
Addition rule: this OR that
12
Q
What is incomplete dominance?
Give an example.
A
BB, Bb, bb are are phenotypically different. Where Bb is an intermediate between two extremes.
Ex. red, white and pink, flower
13
Q
What is codominance?
Give an example.
A
BB, Bb, bb are are phenotypically different.
Bb exhibits phenotypes of both homozygotes.
ex. spotted cow
14
Q
There can be a single nucleotide mutation at any part of a locus that can affect the gene in different ways. True or False?
A
True.
15
Q
The frequency of a particular allele is usually the same from one population to another. True or False?
A
False. The frequency of a particular allele often varies from 1 population to another.
16
Q
When it comes to blood type, Gene I encodes for _____ enzyme.
A
When it comes to blood type, Gene I encodes for transferase enzyme.
17
Q
How do transferase enzymes differ? What are the symbols associated with these differences?
A
I^A –> encodes transferase which adds acetylgalactosamine
I^B–> encodes transferase which adds galactose
i–> encodes nonfunctional transferase
I^A I^B –> encodes transferase with acetylgalactosamine and galactose
Note*: AB alleles are codominant and 2 distinct proteins are made
18
Q
When an enzyme/ protein is no longer being produced, is produced at lower levels, or is nonfunctional, its alleles are considered to be _______ alleles.
A
When an enzyme/ protein is no longer being produced, is produced at lower levels, or is nonfunctional, its alleles are considered to be loss of function alleles.
19
Q
A loss of function allele is dominant over a wildtype allele. True or False?
A
False.
Not always. Wild type is dominant over recessive loss of function. Dominant loss of function is dominant over wild type.
20
Q
What is haplosufficiency?
A
Haplosufficiency occurs when a wildtype allele is mixed with a loss of function allele.
Half as much protein is synthesized, yet this is often sufficient to achieve the wildtype phenotype.
21
Q
The dominant allele is always considered to be the normal allele, and the recessive allele is considered a mutation. True or False?
A
False. The dominant allele is not always considered to be normal, sometimes the dominant allele is considered to be a mutation.
ex. Dominant alleles can be gain of function or loss of function mutations
22
Q
What is a gain of function allele?
A
Gain of function allele –> mutant dominant allele which produces a protein that has an increased function
(This is often detrimental)
ex. Huntington’s disease
23
Q
What is needed to cause a recessive lethal allele death?
A
Need both copies of the allele
24
Q
Lethal genes can only be expressed in homozygotes. True or False?
A
False. Dominant lethal genes can be expressed in both the heterozygote and homozygote.
They can be dominant and recessive.
25
How are dominant lethal alleles passed down?
Lethal alleles can cause death after the age of reproduction, meaning those dominant genes have the ability to be passed down.
26
What is the result of a dominant-negative allele?
The dominant-negative allele is has a polypeptide that interferes with wildtype polypeptide. This causes a severe mutant phenotype.
27
What is penetrance?
Penetrance- The proportion of individuals having a particular genotype that express the expected phenotype.
aka. variation in the population
28
What is expressivity?
Expressivity- The degree to which a phenotype is expressed (mild to severe).
aka. variation in the individual
29
What are the types of penetrance?
- Complete penetrance (100% expected phenotype)
| - incomplete penetrance (<100% expected phenotype)
30
What are the types of expressivity?
- Constant expressivity (100% expressed phenotype)
| - Variable expressivity (range of phenotypes)
31
Briefly explain incomplete penetrance with variable expressivity.
Identical known genotype produce a broad range of phenotypes due to varying degrees of gene activation and expression.
32
What are some environmental factors that can affect phenotypic expression?
1. Age
2. Sex
3. Temperature
4. Chemicals
33
The range of phenotypes expressed by a single genotype under different environmental conditions is referred to as the _______.
The range of phenotypes expressed by a single genotype under different environmental conditions is referred to as the norm of reaction.
34
Environmental factors alone cannot produce phenotype that is the same as the phenotype of an individual with another genotype. True or False?
False. Environmental factors alone CAN produce phenotype that is the same as the phenotype of an individual with another genotype.
ex. himalayan allele in rabbits
35
What is a phenocopy?
A change in phenotype arising from environmental factors that mimic the effects of a mutation in a gene.
Ex. can phenotypically copy a disorder from a chemical
36
Can controlling environment influence appearance of mutant phenotype?
Yes.
ch5, slide 43
37
Different combinations of alleles from two or more genes can result in different phenotypes, because of interactions between their products at the cellular or biochemical level. True or False?
True. This is called genetic interactions.
38
When considering complete dominance at two gene pairs contributing to a single trait, what is a dilute gene?
The "original" allele.
| ex. blue eyes (recessive)
39
Complementation will only occur if the mutations are on the same genes. True or False?
False. Complementation will only occur if the mutations are on different genes.
40
When does complementation occur?
Complementation occurs when two strains of an organism with different homozygous recessive mutations that produce the same phenotype, produce offspring of the wild-type phenotype when mated or crossed.
41
What is a heterogenenous trait?
A mutation in any one of a number of genes can give rise to the same phenotype.
ex. deafness can be caused by a number of different genes.
42
What is epistasis?
The masking of the expression of one gene by another. No new phenotypes are produced.
43
What is the difference between and epistatic gene and a hypostatic gene?
The “epistatic gene” --> does the masking.
| The “hypostatic gene” --> is masked
44
What are the F2 ratios for the following monohybrid crosses:
| Complete dominance, Incomplete dominance/ codominance, recessive lethal allele.
Complete dominance --> 3:1
Incomplete dominance/ codominance --> 1:2:1
Recessive lethal allele --> 2:1
45
What are the F2 ratios for the following dihybrid crosses:
| Complete dominance, Recessive epistasis, Complementation, Dominant epistasis.
Complete dominance --> 9:3:3:1
Recessive epistasis --> 9:3:4
Complementation --> 9:7
Dominant epistasis --> 12:3:1
46
What is pleiotropy? Give an example.
A single gene can be responsible for a number of distinct and seemingly unrelated phenotypic effects.
ex. sickle cell anemia, cystic fibrosis
47
What are inbred lines?
| Hint: plants
Self-fertilized plants that are homozygous for alleles that were present in the founding line.
48
Hybrid plants usually grow taller and faster than inbreds. True or False?
True.
49
What is heterosis/ hybrid vigor?
When two different inbred lines are crossed, the hybrids are heterozygous for many genes.
These plants are usually taller and grow faster --> vigor.
50
What is the Hardy Weinberg equation?
When it comes to proportion:
p^2 x 2pq x q^2 = 1
When it comes to frequency (if there are only two alleles):
p + q = 1
51
The Hardy Weinberg principle is correct in the absence of what influences? Give 2.
1. Nonrandom mating
2. Unequal survival
3. Population subdivision
4. Migration
52
What is dosage compensation?
A way of equalizing gene expression in the face of different gene dosage.
(inactivation of 1/2 X chromosomes in females).
53
What causes the non-homologous X and Y genes to pair up during meiosis?
The pseudoautosomal regions of X and Y chromosomes are homologous.
Top: primary
Bottom: secondary
54
An individual can have anuploidy for sex chromosomes and still display sex-determined characteristics. This is called ______.
An individual can have anuploidy for sex chromosomes and still display sex-determined characteristics. This is called viable anuploidies.
55
A Barr body will be present in the nucleus every time an individual has _________.
A Barr body will be present every time an individual has 2 X alleles.
56
What does it mean when people say females are functionally hemizygous for X-linked genes?
Approximately 50% cells express one allele, and 50% cells will express the other allele.
57
Give an example of a female genetic mosaic.
Females that are heterozygous for X-linked traits.
ex. Red-green colour blindness in one eye.
58
Ants, Bees and Wasps have polyploidy males. True or False?
False. Ants, Bees and Wasps have monoploidy (N) males.
59
Polyploidy is common in plants and animals. True or False?
False. Polyploidy is common in plants but is rare in the animal kingdom.
(Polyploidy animals are often sterile)
60
What are autopolyploids?
Individuals where the chromosome sets are all identical.
All chromosomes are derived from the same species. (non-disjunction in meiosis 1)
Autopolypoids usually have:
- Less seed production
- More vegetative growth
61
Many polyploids are sterile due to problems with _____ and ______ of homologous chromosomes in meiosis.
Many polyploids are sterile due to problems with pairing and separation of homologous chromosomes in meiosis.
62
What are the possibilities of occurrence in Meiosis 1 of a 3N=33 banana?
1. 11 trivalent (all stay together
| 2. 11 bivalent, 11 univalent (2 paired, leaving one out)
63
What is an allopolyploid?
A popyploid as the result of a cross between two or more species.
64
Allohexaploid and amphidiploid are the same thing. True or False?
```
True.
Allohexaploid: 6N=42
(chromosomes of different species)
Amphidiploid: 3N=42
(how many diploids you have within; bivalents)
```
65
When producing a polyploid hybrid through a inter species cross, what is the goal?
The goal is for hybrid to have only beneficial traits.
66
Chromosome doubling which could potentially restore fertility is not well tolerated in animals. True or False?
True.
67
What is aneuploidy?
A diploid genome which lacks a chromosome or has an extra chromosome.
Trisomy & monosomy
68
What are potential causes for aneuploidy?
Meiosis 1 non-disjunction: 2 trisomies, 1 monosomies.
Meiosis 2 non-disjunction: 1 trisomy, 1 monosomy, 2 normal gametes
69
What are some examples of viable trisomies in humans?
Trisomy 21 --> down syndrome
trisomy 13 --> pautau syndrome
trisomy 18 --> edwards syndrome
70
What are some aneuploid conditions in human sex chromosomes?
- X0 Turner Syndrome
- XXY Klinefelter Syndrome
- XXX Triple X Syndrome
- XYY Double Y male
71
What happens in prophase 1 that contributes to higher chances of auneuploidy in gametes of females as they age?
Female eggs are arrested in prophase 1. They start to ofind their homologous pairs and start crossing over (recombinantion).
Joining and disjoining losens homologous pairs and they don't separate properly.
*If bivalent dissociates, nondisjunction of the homologues occurs.
72
Deletion/ Deficiency is a _______ chromosome segment.
| This is also called _______.
Deletion/ Deficiency is a missing chromosome segment.
| This is also called hypoploidy.
73
Duplication is an _____ chromosome segment.
| This is also called _______.
Duplication is an extra chromosome segment.
| This is also called hyperploidy.
74
A chromosome can't be rearranged internally, but it can become joined to another chromosome. True or False?
False. A chromosome may become rearranged internally, or it may become joined to another chromosome
75
What are the types of chromosomal inversions? Give a brief description of each.
Pericentric inversion:
- includes centromere (swap above and below centromere)
Paracentric Inversion:
- occurs below centromere
- when alleles of homologous chromosomes don't align properly, inversion loop is formed (prophase 1) to allow homologous sequence to align
*Bottom chromosome loops on its own to reinstate correct order
76
Translocation occurs with homologous chromosomes. True or False?
False. Translocations occur when a segment from one chromosome is detached and reattached to a different (nonhomologous) chromosome.
77
What is a reciproal translocation?
Translocation where pieces of two non-homologous chromosomes are exchanged without any net loss of genetic material.
*In prophase 1, homologous chromosomes form a crosslike configuration.
78
How are compound chromosomes formed?
Compound chromosomes are formed by the fusion of homologous chromosomes, sister chromatids, or homologous chromosome segments.
-Formed by robertsonian translocations
79
When two non-homologous chromosomes fuse at their centromeres it is called ______.
(*Hint: 2 acrocentric chromosomes = 1 metacentric chromosome & small fragment)
When two non-homologous chromosomes fuse at their centromeres it is called Robertsonian translocations.
80
Why do some dihybrid crosses act as a simple complete dominance (24:8)?
- The R and L genes are linked on the same chromosome (RL and rl alleles segregate as linked genes)
- There is some infrequent exchange between the chromosomes that harbor RL and rl
- This exchange is called recombination
81
How do we calculate frequency of recombination?
Frequency = (#of recombinants / total) x 100%
82
In F1 of a dihybrid cross, you will get 4 classes of equal frequencies if the genes are linked. True or False?
False. In F1 of a dihybrid cross, you will get 4 classes of equal frequencies if the genes are NOT linked.
*If genes are linked get 2 major and 2 minor classes of offspring.
83
Homologous recombination occurs during ______ of meiosis.
Homologous recombination occurs during PROPHASE 1 of meiosis.
84
Generally speaking, a tetrad is the same thing as a bivalent. True or False?
True.
85
What is a chiasma?
Physical unction between the homologous chromatids.
| It is the site where recombination occurs.
86
The further apart genes are from one another on a chromosomes, the more likely they are to have recombinants. True or False?
True.
| Genes far apart = more likely to cross independently --> increases likelihood of recombination.
87
If you know the frequency of recombination in a specific gene pair how would you determine their distance from one another.
Frequency = ___ map units
88
Frequency = map units begins to plateau around ____% because at _____ map units, genes start to independently assort even if they're on the same gene.
Frequency = map units begins to plateau around 50% because at 50 map units, genes start to independently assort even if they're on the same gene.
89
Pedigree analysis provides estimates of recombination frequencies to map genes on human chromosomes. True or False?
True.
90
What makes bacteria valuable research objects? Give 2-3 points.
- Small size
- Rapid reproduction
- Selective media (e.g., antibiotics) that can easily identify the presence of an active allele
- Simple structures and physiology
- Genetic variability
91
Bacteriophages produce clearances called _____ on plates with dense bacterial cultures within hours of infection.
Bacteriophages produce clearances called PLAQUES on plates with dense bacterial cultures within hours of infection.
92
What are some differences between bacteriophage T4 and Lambda?
T4:
- Contains around 170 000 base pairs and 150 characterized genes
- fairly large and complex genome
- Phage goes through lytic phase to infect other cells (provides for quick and simple genetic experiments)
Lambda:
- Contains around 50 000 base pairs and 50 genes
- May be in lytic or lysogenic phase
93
All bacteriophages are considered to be _______.
All bacteriophages are considered to be RETROVIRUSES.
94
Explain the process of how retroviruses work.
| 9 steps
1. Virus attaches to host cell at receptors in membrane.
2. Viral core enters the host cell.
3. Viral RNA uses reverse transcriptase to make complementary DNA; viral RNA degrades.
4. Reverse transcriptase synthesizes 2nd DNA strand.
5. Viral DNA enters nucleus & is integrated into the host chromosome, forming a provirus.
6. On activation, proviral DNA is transcribed into viral RNA --> is exported to the cytoplasm.
7. In cytoplasm, viral RNA is translated to proteins.
8. Viral RNA, proteins, new capsids, & envelopes are assembled.
9. Assembled virus buds from the cell membrane.
95
What will cause a virus to go into the dormant phase?
- Bacteria doesn't have enough nutrients
- Bacterial colony is drying for some reason.
*Virus will wait for host population to be healthy again.
96
When phage DNA integrates into the bacterial chromosome, what does it become?
(Hint: lysogenic cycle)
When phage DNA integrates into the bacterial chromosome, it becomes a prophage.
97
What are plasmids? How do they replicate?
Plasmids are additional genetic material (small circular DNA) that can replicate independently of the chromosome.
98
What are episomes? How do they replicate?
Episomes are harge circular DNA that can integrate into the bacterial chromosome for replication or can remain separate.
99
Gene transfer in bacteria is _______.
| Hint: from donor cells to recipient cells
Gene transfer in bacteria is unidirectional.
100
What are some ways gene mutations can be observed in bacteria. List 2-3.
- Colony colour and morphology
- Nutritional mutants (can not metabolise certain sugars, like lactose or galactose)
- Prototrophs and auxotrophs (can not make certain amino acids, these need to be added to the growth medium)
- Antibiotic resistance
101
What conclusion can you make from a replica plating experiment?
A colony that grows ONLY on the supplemented medium has a mutation in a gene that encodes the synthesis of an essential nutrient.
102
What are some methods of recombination occurring in bacteria?
(Hint: parasexual process)
1. Transformation
- transfer of a free ( out of cell) piece of DNA from 1 bacterium into another
Conjugation:
-direct transfer of DNA from one cell to another via establishment of a cytoplasmic bridge
Transduction:
- transfer of genes from one cell to another via bacteriophage
103
which of the 3 parasexual processes are sensitive to DNase? Why?
Transformation. In this process the DNA is exposed to the environment outside of the cell.
104
What does it mean if a bacterium is competent? What process does this refer to?
A competent bacterium can bind to exogenous DNA and transport it into the cell.
(It has a DNA receptor and translocation complex)
This is beneficial in transformation.
105
The rate of cotransformation in bacteria is inversely proportional to _____.
The rate of cotransformation in bacteria is inversely proportional to gene distances.
(ch.9, slide 25)
106
Conjugation is a kind of bacterial "sexual" reproduction, mediated by the _______.
Conjugation is a kind of bacterial "sexual" reproduction, mediated by the Fertility factor.
107
The Fertility factor is a type of plasmid. True or False?
False. The F factor is a type of episome.
108
Describe the process of mating & conjugation of fertility factors.
(4 steps)
1. F pilli of F+ donor cell make contact with F recipient cell & pulls them together.
2. Genes on f-factor direct the synthesis of conjugation bridge. 1 strand of DNA is cleaved at origin of f-factor replication.
3. Rolling circle replication transfers 1 strand of f-factor into recipient cell. Replication of f-factor occurs in both cells (1 in each) during transfer.
4. Transfer of f-factor is completed--> yields 2 F+ bacteria.
109
What is an Hfr cell?
A cell whose F-factor is integrated into its bacterial chromosome.
*This cell chromosome will nick at the F-factor, and will conjugate to transfer specific genetic information.
110
Genes located close to one another are more likely to be co-transducted. True or False?
True.
111
What are some functions of genetic material?
- Replicate
- Control growth & development of organism
- Allow organism to adapt to changes in the environment
112
What was the Griffith experiment and what was its conclusion?
Virulent bacteria, non virulent bacteria, heat killed virulent bacteria, non-virulent + heat killed virulent bacteria.
Conclusion: A substance in the heat-killed virulent bacteria genetically transformed the non-virulent bacteria into live, virulent bacteria. (Bacteria can pick up environmental DNA).
113
What was the Avery, MacLeod, McCarty experiment and what was its conclusion?
Virulent bacteria treated with protease, RNase, or DNase.
| Conclusion: Since only DNase destroyed the transforming substance, the transforming substance must be DNA.
114
What was the tabacco mosiac virus (TMV) experiment and what was its conclusion?
Take off protein from RNA, create hybrid virus (red rna with blue proteins).
Conclusion: The type of RNA in hybrid TMV determines the RNA and protein of the progeny viruses
115
Nucleic acids are composed of ______.
Nucleic acids are composed of NUCLEOTIDES.
116
What are nucleotides composed of?
- Nitrogen-containing bases
- Pentose sugar
- Phosphate (phosphodiester bond)
117
What are the nitrogen-containing bases?
```
A = Adenine
T = Thymine
G = Guanine
C = Cytosine
U = Uracil
```
118
What are the types of sugars in nucleotides?
- Deoxyribose
| - ribose
119
What nitrogen bases are purines?
Adenine, Guanine
120
What nitrogen bases are pyrimidines?
Cytosine, Thymine, Uracil
121
Purines are bigger than pyrimidines. True or False?
True.
122
Nucleotides are joined together by ______ bonds.
Nucleotides are joined together by phosphodiester bonds.
123
What did Erwin Chargaff discover?
purines = pyrimidines
124
What are some assumptions of the Watson- Crick model?
Assumptions:
- DNA is a double helix
- The two strands were anti-parallel
- The sugars form a phosphate backbone
- The bases are held together by H bond
125
How many bonds are found between T and A? What kind of bonds are they?
2 H-bonds.
126
How many bonds are found between C & G? What kind of bonds are they?
3 H-bonds.
127
What are the distances of the minor and major groves of DNA?
Minor: 0.34nm
Major: 3.4 nm
128
To coil a strand of DNA, you need to introduce a _______.
To coil a strand of DNA, you need to introduce a single nick.
129
What is ligation?
| Hint: DNA coiling
Ligation: strand needs to seal the nick created so that it is able to keep energy inside & the coil doesn't unravel.
130
What are the dimensions of an E. coli DNA strand and cell?
DNA: 1.5mm circle
Cell: 2microm x 1 microm
131
How is bacterial chromosome formed?
| 3 stages + size
Circular unfolded: 350microm
40-50 loops: 30microm
Supercoiled & folded: 2microm
*Has one genome (monoploid)
132
What are the types of proteins found in eukaryotic chromosomes?
- 5 histones (Highly positively charged polypeptides)
| - A divergent group of non-histone proteins
133
What is Chromatin?
| Hint: equation
Chromatin = DNA + Histones + Protein
134
What does each nucleosome core consist of?
Nucleosome core consists of an octamer of histones (11nm).
| Octamer: 2 of each H2a, H2b, H3, H4
135
Nucleosome core has ___ nucleotide pairs of DNA wrapped as ___ turns around an octamer of histones.
(Hint: both answers are numbers)
Nucleosome core has 146 nucleotide pairs of DNA wrapped as 1.75 turns around an octamer of histones.
136
How many nucleotide pairs does the linker of a nucleosome have? What is its size?
Has 8-113 nucleotide pairs. Is 2nm wide.
137
The complete nucleosome contains histone ____.
The complete nucleosome contains histone H1.
138
What is the size of chromatin fiber?
30nm.
139
Chromatin fiber is also called _____.
Chromatin fiber is also called solenoid.
140
In the 3rd level of packaging of a chromosome, the 30nm chromatin fiber is attached to the 300nm chromosome ________.
In the 3rd level of packaging of a chromosome, the 30nm chromatin fiber is attached to the 300nm chromosome scaffold.
