Populations & Evolution

Question 1

What is allele frequency?

Answer 1

How often an allele occurs in a population (eg. t=0.05 = 5% of all alleles of that gene are t)

Question 2

What is the Hardy-Weinberg principle?

Answer 2

A mathematical model that predicts the frequency of alleles, genotypes and phenotypes in a population. Predicts the frequency of alleles of a gene stay constant over generations

Question 3

Hardy-Weinberg assumptions

Answer 3

• No mutations
• No selection
• Random mating
• Large, isolated population (no genetic drift)
• No migration

Question 4

Allele frequency equation

Answer 4

p + q = 1

p = frequency of dominant allele
q = frequency of recessive allele

Question 5

Genotype frequency equation

Answer 5

p^2 + 2pq + q^2 = 1

p^2 = frequency of homozygous dominant genotype
2pq = frequency of heterozygous genotype
q^2 = frequency of homozygous recessive genotype

Question 6

What is intraspecific variation?

Answer 6

Variation within a species (individuals of same species have same genes but different alleles / different phenotypes)

Question 7

What is interspecific variation?

Answer 7

Variation between a species (individuals of different species have different genes and different environments / different phenotypes)

Question 8

Causes of variation

Answer 8

• Mutations
• Meiosis (independent segregation, crossing over)
• Random fertilisation
• Environment changes phenotype over time

Question 9

What is evolution?

Answer 9

Change in allele frequency over time, through genetic drift or natural selection

Question 10

What is genetic drift?

Answer 10

Change in allele frequency over time due to random chance (random fertilisation means it’s random which alleles pass to the zygote). Affects small populations more

Question 11

Disruptive selection

Answer 11

• Both extremes of the phenotype more likely to survive + reproduce
• Environment selects for two separate phenotypes
• Contributes to sympatic speciation

Question 12

What is speciation?

Answer 12

The process of forming a new species. Can be allopatric (geographically and reproductively isolated) or symatic (not geographically isolated but are reproductively isolated)

Question 13

Speciation process

Answer 13

• Variation exists in population due to mutations
• Different selection pressures lead to directional selection of different phenotypes
• Differential reproductive success
• Leads to a change in allele frequency over many generations

Question 14

Mechanisms of reproductive isolation

Answer 14

• Mechanical (different shaped genitalia)
• Behavioural (different courtship behaviour)
• Seasonal (reproductively active at different times of year)
• Hybrid sterility (hybrid of two species infertile)