Population Genetics

Question 1

species

Answer 1

– All members of the same species can
interbreed and produce fertile offspring
– not all have the opportunity

Question 2

Population

Answer 2

– A group of organisms within the same
species that do have the opportunity to
interbreed
- Capable of gene flow

Question 3

Phenotypes

Answer 3

• Phenotypes appear with different frequencies in the
  population
• E.g. albinism – in humans and animals it is a relatively
  rare trait compared to the wild pigmented
  phenotype

Question 4

Allele Differences

Answer 4

• The variability of phenotypes in an individual population
  (human or animal) is due to allele differences

Question 5

Allele Frequencies

Answer 5

Differences in the frequency of phenotypes in a population
must be due to differences in allele frequencies

Question 6

Frequency Given As

Answer 6

% or
decimal fraction

Question 7

What happens to allele frequencies during genetic
crosses?

Answer 7

• If there are two alleles that determine a phenotype, the
  frequency of those two alleles will add up to 100%
• Frequencies of alleles are designated by p and q
  – p = frequency of one allele
  – q = frequency of the other allele
• p + q = 1

Question 8

HW LAW

Answer 8

Allele frequencies remain the same throughout generations

• Random mating must happen
• Populations must be large
• No selection pressures
• Immigration or emigration

Question 9

Evolutionary changes in allele frequency

Answer 9

Original Species—–> 2 populations form——-> populations interbreed——> Barrier to mating

Question 10

Factors causing Hardy-Weinberg law to break down

Answer 10

1. Small populations  chance events
   a) Genetic drift (random loss or gain of alleles)
   b) Bottleneck effect

Question 11

Bottleneck Effects

Answer 11

a sharp reduction in population size
due to environmental effects resulting in a loss of genetic
diversity

Question 12

2.Founder Effects

Answer 12

loss of genetic variation that occurs
when a new population is established by a very small
number of individuals from a larger population
* Founder effects example: Retinitis pigmentosa on
Tristan de Cuhna (night blindness)
* Island was first colonised in 1810 by 15 people
– Just one person had night blindness
– Current population today has a high frequency of the condition

Question 13

Mutational Change

Answer 13

Before evolution can happen, genetic variation must exist within a population
Allele frequencies change over time because some
alleles mutate into others
Eventually, these alleles become fixed in the population

Question 14

Assortative Mating

Answer 14

• Assortative mating: a mating pattern and form of sexual
  selection where individuals with similar phenotypes mate
  with one another more frequently than expected
• E.g.Bufo toads commonly choose mates based on size
  – Large toads choose large toads
  – Small toads choose small toads

Question 15

The direction and magnitude of change depend on:

Answer 15

– Selection intensity
– Dominance relations of the alleles
– Allele frequencies

Question 16

Mechanisms that cause
allele frequency changes

Answer 16

1. Small populations  chance events
2. Founder effects
3. Gene flow between populations (migration)
4. Mutational changes
5. Non-random mating
   – Inbreeding (e.g. Hapsburg Lip and Jaw)
   – Selfing
6. Assortative mating – mate choice
7. Natural selection (important)