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Genetics > Tutorials for Midterm > Flashcards

Tutorials for Midterm Flashcards

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1
Q

What is the C-value? What is it measured in?

A

the mass of a haploid genome

measured in picograms

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2
Q

In the equation 2n=4 what does each of these things stand for?

A

2 is the ploidy (diploid)
n is the number of different chromosomes
4 is the total number of chromosomes in the cell

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3
Q

During what phase is DNA replicated?

A

S (synthesis)

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4
Q

What joins sister chromatids?

A

centromere

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5
Q

Do homologous chromosomes have the same alleles?

A

no they are different

one from each parent

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6
Q

What happens during prophase of meiosis?

A

chromosomes condense

crossovers occur

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7
Q

What happens during metaphase I?

A

independent assortment, align at the metaphase plate

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8
Q

What happens during anaphase I?

A

homologous chromosomes separate and move towards opposite poles

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9
Q

What happens during telophase I and cytokinesis?

A

the cytoplasm splits creating two daughter cells

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10
Q

What happens during prophase II? How long is it? Do all organisms have it?

A

nothing really because the chromosomes are already condensed and there is no crossover
it is very short
it only occurs in some eukaryotes

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11
Q

What happens during metaphase II?

A

sister chromatids line up at the metaphase plate

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12
Q

What happens during anaphase II?

A

sister chromatids are pulled to opposite poles

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13
Q

What happens during telophase II and cytokinesis?

A

the cytoplasm splits and two daughter cells are created

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14
Q

When during meiosis is there 4C? 2C? C?

A

4C, during G2 after S
2C, after the first round of division
C, after the second round of division

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15
Q

If two genes are unlinked what is the chance of a specific allele occurring?

A

25%

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16
Q

What is cis configuration in reference to two linked alleles?

A

both dominant alleles on one chromosome and both recessive on the other (in a heterozygote)

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17
Q

What is trans configuration in reference to twi linked alleles?

A

a dominant and recessive allele on each chromosome (in a heterozygote)

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18
Q

What is a chiasma?

A

the place where two homologous chromosomes crossover

it is the only physical evidence that crossover has occurred

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19
Q

When does a chiasma form?

A

during early prophase I

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20
Q

If two genes are not linked how often does recombination occur?

A

50% of the time

i.e. there are 4 possibilities

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21
Q

How do you observe if a crossover took place between two homologous chromosomes?

A

you need to observe the phenotypes associated with the genotypes

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22
Q

Why do you use a homozygous recessive parent as the tester when crossing with a heterozygote?

A

the recessive alleles won’t “mask” the alleles contributed by the heterozygote parent

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23
Q

Is it possible to get more than 50% recombination?

A

no

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24
Q

What is the % of recombinant offspring equal to?

A

1/2 the % crossing over
i.e. if 20% cross over 10% will be recombinant (5% of each recombinant)

also equal to the map distance in map units or centiMorgans
ie in there are 10% recombinant offspring the loci are 10 map units apart

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25
If two genes are linked what is their map distance?
less than 50 map units
26
How do you identify if 3 genes are in cis or trans configuration?
go in terms of the dominant alleles, can do it for each pair all dominant together = cis other than that there are combinations of cis and trans
27
When you do a three-point test cross how many progeny phenotypes are possible? How do you know which are the parent configurations? The double CO configurations?
8 2 parental, 4 single CO and 2 double CO parental are the most abundant double CO are the least abundant
28
How do you figure out which gene is in the middle when you perform a three-point test cross?
compare the parental phenotypes with the double crossover phenotypes and look for the "odd man out"
29
How do you calculate the distance between 2 genes?
``` # of progeny with a crossover between the two genes (both double and single COs, should be 4 numbers) / the total # of progeny x100 (gives the mu or % RO) ```
30
What is interference?
crossovers have a limited amount of time and space to occur and thus crossovers in one area can interfere with crossovers in another area
31
How do you calculate the expected DCO?
multiply the probability of an AB CO by the probability of a BC CO
32
How do you calculate the coefficient of coincidence? Interference?
``` CoC= observed DCO/ expected DCO Interference= 1-CoC ```
33
What does it mean if interference is positive? Negative?
positive means one crossover is affecting another | negative means that one crossover is facilitating another
34
What is a forward mutation?
changes a WT allele to a different allele
35
What is a reverse mutation?
changes a mutant allele back to a WT allele
36
What are the 2 subtypes of substitutions?
transitions and transversions
37
What is a transition?
purine to purine or pyrimidine to pyrimidine
38
What is a transversion?
purine to pyrimidine or vice versa
39
What is an inversion?
a 180 degree rotation of a piece of DNA
40
What is a translocation?
the movement of DNA between non-homologous chromosomes
41
What occurs more frequently, loss or gain of function mutations?
loss of function
42
What are the 2 possibilities for a loss of function mutation?
the function can either be reduced or eliminated
43
What are the 2 possibilities for a gain of function mutation?
enhanced function or an alternate (new) function
44
What is a silent mutation? Do they have phenotypic changes? What kind of mutations do they include?
silent means the protein itself doesn't change there can still be phenotypic changes though i.e. codon usage, regulatory changes this includes synonymous mutations
45
What is a synonymous mutation?
changes the codon but not the amino acid coded for
46
What are two types of non-synonmous mutations?
Missense mutations | Nonsense mutations
47
What are the 2 types of missense mutations?
Conservative- similar amino acid | Nonconservative- non-similar amino acid
48
What is the average mutation rate per gene affecting phenotype? (spontaneous)
2-12 x 10^-6
49
Name 4 factors affecting mutation rate
gene size gene sequence tissue type (i.e. skin will get damaged a lot) number of cell divisions prior to gamete production (for gametes)
50
What is an endogenous mutation? Exogenous?
endogenous is spontaneous | exogenous is induced
51
Name 3 endogenous mutational events
oxidation depurination deamination
52
What causes oxidation to DNA? Where do these species come from?
cause by reactive oxygen species (ROS) | produced by natural cellular processes, but environmental stress i.e. heat, UV can increase the amount of them
53
What are 2 mechanisms used to combat ROS?
enzymes- superoxide dismutase, catalases | antioxidant molecules- vitamins (ascorbic acid, tocopherol)
54
What does oxidation do to DNA?
affects how guanine base pairs, makes it pair with A | get a GC to TA transversion
55
How often does hydrolysis of purines occur in human cells? (depurination) What is the result?
about 1000 times per hour | use lose an A or G base and put a random one back in
56
What does deamination do to DNA?
it removes the amino group off of C making it U U pairs with A causes a CG to TA transition
57
Name 8 types of exogenous mutational events
``` X-ray radiation UV light Base analogs Hydroxylating agents Alkylating agents Deaminating agents Intercalating agents ```
58
What does X-ray radiation do to DNA? What does it cause?
breaks the sugar-phosphate backbone | can cause a huge deletion
59
What does UV light do to DNA? How can this be fixed?
causes pyrimidine dimers (thymine usually) | SOS repair system that uses error-prone polymerases can be used to fix it
60
Explain how 5-bromouracil works as a base analog
the keto form pairs with A the enrol (rare ionized) form pairs with G can bind with an A, tautomerize and then have G put in during replication this results in a TA to CG transition
61
What do hydroxylating agents do? What happens as a result?
they add a hydroxyl group (OH) hydroxylate C, now it base pairs with A results in a CG to TA transition
62
What do alkylating agents do? What happens as a result?
they add ethyl or methyl groups can add to G or T mispaired G pairs with T (and vice versa) causes a GC to AT transition (or TA to GC)
63
What do deaminating agents do? What happens as a result?
``` they remove an amino group Nitrous acid (HNO2) Changes C to U (mispairs with A) Changes A to hypoxanthine (mispairs with C) cause CG to TA transition (or AT GC) ```
64
What are intercalating agents? Give some examples
flat, planar molecules that insert between bases | ie proflavin, acridine orange and ICR-191
65
What happens as a result of intercalating agents?
insertions and deletions (when you are trying to remove them)
66
What test is used to test for mutagenicity? What bacteria are used? What is special about them?
Ames test Salmonella typhimurium they are his- (can't produce histidine)
67
Explain the Ames test
put the bacteria in a tube with a suspected carcinogen/mutagen and rat liver enzymes (some need catalytic activity) grow on his- media and see if there are any revertant mutations (his- gone back to WT)
68
What is retinoblastoma? What hypothesis does it follow?
a rare cancer of the retina 40% of cases result from the inheritance of one Rb- allele two-hit hypothesis
69
What is the two-hit hypothesis?
need to lose both alleles (or be born without one and lose one, or be born without either) in order to get the disease
70
What is an oncogene?
one abnormal gene is enough to cause phenotype | gain of function
71
What is a tumour-supressor gene?
haplosufficient loss of function need to non-functional alleles to have mutant phenotype
72
What is the Law of Segregation?
two alleles separate while making gametes then one from each parent come together at fertilization
73
What is the Stay-green gene (Sgr) in peas?
it is a nonsense mutation near the 5' end of the coding sequence if a pea has 2 it stays green instead of turning yellow it is haplosufficient (need to non-functional copies for mutant phenotype)
74
Describe the mutation to the human CCR5 gene (a chemokine receptor) and the resulting phenotypes
small 32 bp deletion on chromosome 3 affects T cell function heterozygous have reduced susceptibility to HIV and delayed onset of AIDS homozygous for the mutation are resistant to HIV
75
What is a good way to track deletions?
using PCR and gel electrophoresis
76
What is a haplotype?
haploid genotype…talking about one allele a combination of two or more DNA marker alleles that are close together and therefore stay associated over many generations
77
What is linkage disequilibrium?
the non-random association of alleles at two or more loci
78
What do you do in a haplotype-based study?
look for linkage disequilibrium between sections of chromosomes and phenotypes
79
Are most SNPs biallelic?
yes most only have 2 alleles

Genetics (5 decks)

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