Genetics of Populations

Question 1

What is the gene pool?

Answer 1

every copy of every allele at every locus in a population

Question 2

What does it mean if an allele is fixed in a gene pool?

Answer 2

If only one allele exists in a particular locus

Question 3

What happens in the absence of any evolutionary force?

Answer 3

Nothing! The population’s genotype and allele frequencies don’t change. HWE describes a population that isn’t evolving

Question 3

What are the assumptions of the Hardy-Weinberg Principle?

Answer 3

• there is no mutation
• the population is infinitely large (otherwise random genetic drift will occur)
• mating among individuals is random
• individuals are not moved into or out of the population (otherwise, gene flow will occur)
• all individuals have equal probabilities of survival and reproduction (otherwise natural selection will occur)

Question 3

Hardy-Weinberg Principle

Answer 3

Whatever the initial genotype frequencies for two alleles may be, after one generation of random mating, the genotype frequencies will be: p^2: 2pq: q^2

Question 4

What is the significance of the Hardy-Weinberg Principle?

Answer 4

• explains how Mendelian inheritance preserves genetic variation in a population
• Allows testing of whether evolution is occurring in a population (HWE is used as the null model)
• By assuming HWE, we can obtain a rough estimate of the percentage of a population carrying a disease allele

Question 5

Genotype numbers

Answer 5

D: number of AA
H: number of Aa
R: number of aa

Question 6

What is the equation for the total number of individuals (N)?

Answer 6

D + H + R = N

Question 7

Genotype frequencies

Answer 7

d= D/N
h= H/N
r= R/N
d+h+r=1

Question 8

Allele frequencies

Answer 8

p= (2D+H)/2N, or p=d+ h/2
q= (2R+H)/2N, or q=r+ h/2

Question 9

Genotype frequencies in the next generation

Answer 9

d’=p^2
h’=2pq
r’=q^2

Question 10

Extensions of the Hardy-Weinberg Theorem

Answer 10

(p+q)^2 =1
For three alleles: p^2 + 2pq + q^2 +2pr + 2qr + r^2 = 1

Question 11

What is a prerequisite for evolution?

Answer 11

Variation in heritable traits

Question 12

What is evolution?

Answer 12

Descent with modification
Change in the genetic composition of a population from generation to generation

Question 13

What is microevolution?

Answer 13

occurs rapidly within populations and change their genetic makeup from one generation to the next
ex: birds beak size before and after drought

Question 14

What is macroevolution?

Answer 14

occurs slowly, where the history of life is written both in the fossil record and in the relationships of living species
ex: thoracic vertebrae between python and chicken