population genetics - lecture 14

Question 1

what is a locus?

Answer 1

The position in the genome being considered

Question 2

what are alleles?

Answer 2

alternative DNA sequences

Question 3

what are SNPs?

Answer 3

Single Nucleotide polymorphisms

Question 4

How do we get phenotypic difference?

Answer 4

Genes with different alleles that lead to different phenotypes produce genetically- based phenotypic variation

Question 5

How to determine the alleles frequency?

Answer 5

Frequency of A = number of A alleles/ Total number of alleles

Question 6

What is the definition of evolution?

Answer 6

change in allele frequencies over Time

Question 7

What are genotypic frequencies?

Answer 7

Number of individuals with the genotype divided by total number of individuals

Question 8

How to calculate the genotype frequencies for (AA)?

Answer 8

f(AA)= nAA/N

Question 9

5 assumptions of the hardy- Weinberg model

Answer 9

• population is very large
• Random mating
• No migration
• no selection
• No mutation

Question 10

The method behind the Hardy - Weinberg model

Answer 10

Two alleles in a diploid individual are randomly and independently sampled from an infinitely large pool of games

Question 11

Predicted Genotype frequencies for the Hardy- Weinberg model

Answer 11

Freq. homozygous A (AA)= p^2
Freq. homozygous a (aa)= q^2
Freq. heterozygote (Aa)= 2pq

Question 12

what are the 2 Hardy - Weinberg model predications

Answer 12

1 - Allelic frequencies of a population do not change due to random mating

2- Genotypic frequencies are the product of allele frequencies ,and will be at these frequencies after a single generation of random mating

Question 13

How may categories of non random mating are there? which disrupt the H-W assumption

Answer 13

• positive assortative mating = similar individuals tend to mate with each other
• Negative assortative mating= different individuals tend to mate with each other
• inbreeding = individuals tend to mate with relatives

Question 14

what happens when inbreeding occurs?

Answer 14

• offspring produced by inbreeding are more likely to have two alleles that are identical by descent
• These individuals are homozygous, so inbreeding increases homozygosity and reduces heterozygosity

Question 15

How is the proportion of inbreeding measured?

Answer 15

inbreeding coefficient F = probability that two alleles are identical by descent

Question 16

What does F stand for?

Answer 16

proportional reduction in the frequency of heterozygotes compared to that expected in the H-W model

Question 17

What is the inbreeding depression?

Answer 17

Heterozygosity can be advantageous , but inbreeding reduces the percentage of it.

Therefore, inbreeding can lead to reduced fitness

Question 18

How can allele frequencies change?

Answer 18

• Genetic drift
• Natural section
• Migration

Question 19

What is genetic drift?

Answer 19

Random changes in allele frequencies

Question 20

why does genetic drift occur?

Answer 20

In a finite population, the composition of a selected allele frequency will often deviate from that of the parental gene pool

Question 21

what is the expected amount of error due to genetic drift?

Answer 21

1/2N

Question 22

What is a population bottleneck?

Answer 22

When populations go through drastic reductions in population size, it can produce huge ‘ drift events’

Question 23

what is the founder effect ?

Answer 23

when a new population is founded by very few individuals , the allele frequencies can be very different from the original population

Question 24

What is fitness?

Answer 24

The average contribution to the next generation made by an individual or genotype

Question 25

what is overdominance?

Answer 25

Heterozygote has highest fitness. selection maintains both alleles in the population

Question 26

What is migration?

Answer 26

Movement of alleles from one population to another

Question 27

what are the advantages of migration?

Answer 27

• Prevents populations form becoming genetically different

- increases the genetic variation within populations