TOPIC 11: GENETIC POPULATION STRUCTURE

Question 1

Genetic Structure

Answer 1

a description of the genetic variation among individuals within a
population (looking at whole gene pool)
* natural selection requires genetic variation

• Remember… genetic variation is important – reflects the capacity of a population
  to respond/adapt to environmental change

Question 2

Gene flow

Answer 2

(= the exchange of genetic material among populations resulting from
dispersal

Question 3

What does genetic variation depend on?

Answer 3

he number and variability of selection pressures
acting on individuals within a population

• Few selection pressures with low variability – low variation; pop is stable not a lot of changes b/c environment is stable
• Many selection pressures with high variability – high variation

Question 4

How do you quantify level of genetic variation in a population:

Answer 4

evel of heterozygosity (prop. of heterozygotes in the population)
* the more alleles in the gene pool → more possible combinations of
alleles → higher genetic variation

Question 5

What is the general pattern of genetic diversity?

Answer 5

Smaller populations tend to have lower genetic diversity (variation)
than larger populations

Question 6

List the Two mechanisms operating to ↓ genetic diversity over time:

Answer 6

1. Genetic Drift
2. Inbreeding

Question 7

Genetic Drift

Answer 7

random changes in allele frequencies within a population due to chance

• random ~ no discrimination between (or ‘selection of’) individuals with
  favourable or unfavourable traits
• chance ~ unpredictable change in environmental conditions
• Genetic drift occurs in all populations and is a mechanism of evolution
• In small populations - genetic drift occurs at a faster rate and is more
  likely to result in the loss of an allele

Question 8

Inbreeding

Answer 8

mating between relatives
* In small populations the choice of mates can be limited, resulting in increased
probability of mating with relatives
* Inbreeding tends to increase homozygosity and decrease heterozygosity
(related individuals share similar traits)
* Eventually populations can become exclusively homozygous
* If rare, recessive genes are harmful – homozygosity for
recessive genes can result in reduced fitness and increased
mortality

Question 9

Inbreeding Depression

Answer 9

loss of vitality and increased incidence of
disease due to the expression of deleterious recessive alleles when
genetic diversity decreases

Question 10

Black Robin (New Zealand)

Answer 10

1980 - 5 individuals were remaining – one female
* Now – 250 individuals
* Lower fitness = 30% hatching failure (usually ~ 10%)
Cause?
* A good proportion of the sperm are abnormal (non-motile) – so
many eggs are never fertilized…. (low fertilization success

Question 11

What population size is needed to maintain genetic diversity?

Answer 11

1. Effective Population Size – the subset of males and females within a population
   that successfully breed
   * Defines the number of individuals passing genes to successive
   generations
2. Minimum Viable Population – number of individuals necessary to ensure the
   long-term survival of a species
   * Critical in Conservation Biology - allows us to calculate how large a
   population of a particular species should be to assure its long-term
   survival