8 - Population Genetics

Question 1

Gene pool

Answer 1

All the alleles present and carried by the population

Question 2

Population

Answer 2

A group of INTERBREEDING individuals of the same species that inhabit the same space and time

Question 3

Population genetics

Answer 3

Changes in the frequency of alleles in a gene pool over time

Question 4

Locus

Answer 4

Location of a gene/marker on the chromosome

Question 5

Allele

Answer 5

One variant form of a marker at a particular locus

Question 6

Hardy Weinberg Equation

Answer 6

Used to find the frequency of disease alleles in a population and the carrier frequency

Question 7

Frequency of allele “A” in population

Answer 7

• Called p
• the probability that both the egg and the sperm contain the “A” allele is p x p = p2

Question 8

Frequency of allele “a” in a population

Answer 8

• Called q
• the probability that both the egg and the sperm contain the “a” allele is q x q = q2

Question 9

What is required for a population to be in Hardy Weinberg Equilibrium

Answer 9

the observed genotype frequencies must match those predicted by the equation p2 + 2pq + q2

Question 10

How can alleles for recessive disorders persist in the population

Answer 10

• Most recessive alleles are in heterozygotes
• Thus, rare disease-causing recessive alleles persist
  in the population in heterozygote carriers, even if they are lethal when homozygous

Question 11

What conditions are required for allelic frequencies to remain constant over time

Answer 11

• Mating is random
• Allelic frequencies are the same in males and females
• All genotypes have equivalent viability and fertility
• Mutation does not occur
• Migration into the population is absent
• Population is large so that allelic variations do not occur by chance

Question 12

Parameters that influence the transmission of genes from generation to generation

Answer 12

1. Selection
2. Founder effect / Genetic bottleneck
3. Genetic drift
4. Effective population size
5. Endogamy
6. Consanguinity

Question 13

Selection

Answer 13

Can occur when one genotype is more “fit” than another (e.g. lower susceptibility to disease and/or has higher fertility)

Question 14

Heterozygote advantage

Answer 14

An individual heterozygous at a particular locus that exhibits greater biological fitness (e.g. heterozygotes in malarial areas)

Question 15

Founder effect

Answer 15

Disproportionate effect on gene frequencies that can occur when a new population is founded by a small group of individuals from a larger population (e.g. migrant community)

Question 16

Genetic drift

Answer 16

• Random changes in allele frequencies in the absence of selection
• More likely to occur in small populations than large ones
• Can result in a very good, dominant allele being eliminated from the population

Question 17

Endogamy

Answer 17

• Individuals marrying within their own specific community
• Through time this can result in community specific genetic profiles.

Question 18

Consanguinity

Answer 18

• Marriage between close biological relatives
• First cousins who have 1/8 of their genes in common, and so on average their offspring are homozygous at 1/16 of all loci.

Question 19

Fixation

Answer 19

allele becoming 100% of population

Question 20

Extinguished

Answer 20

allele disappears from population (0%)

Question 21

Individual effects of inbreeding

Answer 21

Increases the risk of having a child homozygous for a rare recessive allele

Question 22

Population effects of inbreeding

Answer 22

Results in an excess of homozygotes compared with random mating

Question 23

What can HW equation be used for

Answer 23

• Genetic counselling
• Understanding the genetic basis of complex disease