Topic 4: Mutation

Question 1

What are the three broad types of mutations?

Answer 1

• point mutations
• indel mutations
• chromosomal mutations

Question 2

What are the 5 types of point mutations?

Answer 2

• transition
• transversion
• silent mutation
• nonsense mutation
• missense mutation

Question 3

What is a transition mutation? transversion?

Answer 3

Transition: Pyrimidine to pyrimidine, or purine to purine

Transversion: Pyrimidine to purine

Question 4

What are the pyrimidines? Purines?

Answer 4

Pyrimidine: Cytosine and Thymine

Purine: Adenine and guanine

Question 5

What are silent mutations?

Answer 5

mutations that change codons, but results in the same amino acid in the end

Question 6

What is a nonsense mutation?

Answer 6

a mutation that results in a pre-mature stop codon, so the amino acid is not made

Question 7

What are the two types of missense mutations?

Answer 7

Conservative: changes codon so it results in a different amino acid, but the amino acid is in the same chemical family (basic, acidic) as the OG amino acid

Non-conservative: results in new amino acid, in a different chemical family than the OG amino acid

Question 8

What are indel (insertion/deletion) mutations?

Answer 8

• when a nucleotide is added or deleted from a gene sequence

Question 9

What are frameshift mutations? Why are they usually deletarious?

Answer 9

• the result from indel mutations
• shifts the entire codon sequence if a nucleotide is added or deleted- so all codons after will be a different amino acid

Question 10

What are chromosomal mutations? the four types ?

Answer 10

• larger mutations that effect an entire chromosome
• deletions, translocations, duplications, inversions

Question 11

describe all 4 different chromosomal mutations

Answer 11

Deletions: Large chunk of a chromatid is removed

Translocation: Segment from a chromosome is transferred to another

Duplication: Segment from one chromosome is transferred to its homologous chromosome (duplicates the genes)

Inversion: a segment of a chromosome are is inverted

Question 12

What are transposable elements?

Answer 12

• “jumping genes”
• segments of DNA that can jump from chromosome to chromosome
• Have their own machinery that can cut from their genome and paste elsewhere

Question 13

If a gene duplication occurs, what are the 3 paths it could take?

Answer 13

• selective pressure on both genes, they stay similar
• selective pressure on one gene, one copy degrades
• selective pressure on one gene, one copy acquires a new function

Question 14

What are germline mutations? somatic?

Answer 14

Germline: occur in the gametes, can be passed onto the next generation

Somatic: occurs in somatic cells, not passed onto the next generation

Question 15

What are some of the hypotheses on mutations and their frequency?

Answer 15

1) as we get an increase in effective population size, we get a decrease in mutation rate

2) some people think that with smaller genome sizes there are higher amounts of mutation rates

Question 16

What is mutation rate?

Answer 16

• number of mutations per locus or per nucleotide or per chromosome or per genome

Question 17

Why does mtDNA (Mitochondrial DNA) have a higher mutation rate than nuclear DNA?

Answer 17

• mitochondrial DNA doesn’t have proofreading or repair mechanisms to fix DNA if it becomes mutated
• additionally, mitochondria only comes from eggs (maternal), so this is a small population size, which means more mutations

Question 18

Why does the rate of mutations in sperm increase as men get older, but for women it stays consistant?

Answer 18

• More of a chance of mutations with men, as sperm are made constantly throughout a mans entire life. As men get older, sperm are still made, but more mutations occur as body degrades
• women are born with all the eggs they will ever have their entire life, so they wont mutate.

Question 19

What is the equation for the expected frequency of A allele in the future, for mutations that are permanent

Answer 19

pt = p0 (1-mu)^t

where p0 is the original allele frequency

(1-mu)^t is the probability it wont mutate at a point in the future

Question 20

What is the equation for the expected frequency of A allele in the future, for mutations that are reversable

Answer 20

pt = pt-1(1-mu) + (1-pt-1)V

Where pt-1(1-mu) is the probability of mutating away

and (1-pt-1)V is the probability of mutating back

Question 21

Is mutation an evolutionary force?

Answer 21

• yes! because it is a change in allele frequency
• However, on its it is super weak, and slow

Question 22

What are the 4 potential fitness effect mutations can have?

Answer 22

lethal – deleterious – neutral – advantageous

Question 23

What are 2 ideas researchers have on the fitness effects of mutations

Answer 23

• neutralists think that most mutations are neutral on fitness
• another idea is that most mutations that affect fitness are deleterious

Question 24

what is negative/purifying selection?

Answer 24

the elimination of deleterious mutations by natural selection

Question 25

What are the three evolutionary impacts of mutations?

Answer 25

• mutations are the ultimate source of variation
• only mutations in germline matter evolutionary
• mutations are random with respect to their evolutionary significance

Question 26

Do mutation rates in different species vary?

Answer 26

• potentially, yes. It is thought by some researchers that size of genome is associated with rate of mutation, (ex, single celled organisms mutate super fast) however, this does not account for generation time or generation size

Question 27

Mutation is the source of genetic variation, but will it change allele frequencies on its own?

Answer 27

yes, but incredibly slowly (millions of years)

Question 27

What is the relationship between mutation rate and population size?

Answer 27

• some hypothesize that Lower effective population sizes = higher mutation rates, higher effective pop size = decrease in mutation rates
• some hypothesis that genome size is more connected to mutation rate (smaller genome, higher mutation rate)

Question 28

In the context of the Belfield et al 2021 article, what factors are associated with differences in mutation rate?
What implications does this have for “mutational load”?

Answer 28

?????