5. Genetic Variation: Models & Measurement

Question 1

Mutation

Answer 1

• Increases genetic variation in populations
• Ultimate source of genetic variation

Question 2

Recombination

Answer 2

• Increases genetic variation in populations
• Creates new combinations of mutations

Question 3

Random genetic drift

Answer 3

• Acts to decrease genetic variation in populations
• Random sampling affected every generation

Question 4

Heterozygosity (H)

Answer 4

• Bb or bB
• Recall from mendelian genetics (heterozygote individuals have both alleles)

Question 5

Polymorphism (P)

Answer 5

“having many forms”
-Proportion of gene loci that have 2 or more alleles in a population
-A locus can be polymorphic without being heterozygous

Question 6

Types of Natural Selection

Answer 6

1) Negative (purifying) selection
2) Positive (directional) selection (adaptation)
3) Selection favouring diversity
4) Migration (gene flow)

Question 7

Mutation-selection balance

Answer 7

• Less fit types reintroduced by mutation
• Followed by selection acting to remove them

Question 8

Selection maintaining variation

Answer 8

• Heterozygote advantage
• Frequency-dependent selection
• Fitness varies in space or time
• Umbrella term “balancing selection”

Question 9

Selectively Neutral Variation

Answer 9

• Different types do not differ in their fitness relative to one another
  -New mutations neither eliminated nor retained by selection

Question 10

The Neutral Theory

Answer 10

Most Molecular Variation May be Selectively Neutral
- Negative selection rapidly eliminates detrimental mutations
- Positive selection rapidly fixes beneficial mutations
The only mutations left to create genetic variation are selectively neutral