Maintenance of Genetic Diversity in Large vs Small Populations

Question 1

Major factors that determine genetic diversity in a population

Answer 1

1)Mutation-Most are loss immediately
2)Selection- Removes deleterious alleles and fixes favourable alleles
3)Chance (drift)- Removes alleles by chance
4)Migration- Is not always present
Independently, all these mechanisms reduce genetic diversity.

Question 2

Balancing selection

Answer 2

A crucial process for maintaining genetic diversity. Operates against random processes. The efficiency of balancing selection varies according to the type of genetic variation.

Question 3

Mutations

Answer 3

Deleterious mutations- Continuously removed by selection.
Favourable mutations- Rare, most are lost by chance. if not lost then increase frequency to fixation.
Neutral mutations- Mutated allele has no impact on fitness.
Flip-Flop mutations- Selected for and sometimes against

Question 4

Forms of balanced selection

Answer 4

1) Heterozygote advantage/over dominance- Mutant allele is advantageous as a heterozygote and disadvantageous as a homozygote
2) Freq-dependent selection- Mutant allele is advantageous when rare but disadvantageous when common
3) Genotype x Environmental interactions- Mutant allele is advantageous in some environments but disadvantageous in others.

Question 5

Frequency dependent selection

Answer 5

Balanced polymorphism- allele favoured when rare but selected against when common.
Eg. Resource use by a population: Allele favoured during abundance and selected against during rarity.

Question 6

Maintenance of genetic diversity operating in small and large populations

Answer 6

Large populations- Slow drift of neutral alleles, mutation- selection equilibrium and balancing selection.
Small populations- Big effect of drift, rapid fixation of alleles. Weakly selected alleles become ‘selectively neutral’, Lower mutation selection equilibrium, No balancing to prevent loss of alleles.

Question 7

Summery

Answer 7

Balancing selection, Frequency dependent selection and genotype x environmental interactions. These all operate to retain genetic diversity in large populations.
As populations get smaller, these processes fall apart, they become overwhelmed by random genetic drift.