3.7.3.2 Speciation and genetic drift

Question 1

Define species

Answer 1

Organisms able to breed to produce FERTILE offspring

Question 2

Define gene pool

Answer 2

All of the alleles for all the organism’s genes in a population

Question 3

Define speciation

Answer 3

Formation of a new species from an existing species (caused by disruptive selection)

Question 4

How does speciation occur?

Answer 4

1. Populations become REPRODUCTIVELY ISOLATED
2. There are SEPARATE GENE POOLS
3. DIFFERENT SELECTION PRESSURES
4. SELECTION of different features (aka different ALLELES)
5. New species arise when genetic differences mean they re unable to interbreed to produce fertile offspring

Question 5

Define allopatric speciation

Answer 5

Formation of new species from different populations in different areas

Question 6

Define sympatric speciation

Answer 6

Formation of new species from population living in same area (without geographical isolation)

Question 7

6 ways sympatric speciation occurs

Answer 7

1. SEASONAL ISOLATION - different flowering and mating seasons
2. BEHAVIOURAL ISOLATION - courtship rituals are not attractive to main population
3. MECHANICAL ISOLATION - change sin genitalia prevent successful mating
4. GAMETE INCOMPATIBILITY - sperm killed in female’s reproductive tract
5. HYBRID INVIABILITY - embryo doesn’t develop
6. HYBRID INFERTILITY - offspring of 2 closely related species incapable of reproducing (due to inheriting different numbers of chromosomes that cannot form pairs during meiosis)

Question 8

What is genetic drift?

Answer 8

• Chance determines whether organisms survive and reproduce

- Change in allelic frequencies in SMALL populations

Question 9

What is the Founder Effect? & example

Answer 9

• Type of genetic drift
• Migration of a small number of the population
• A new population of established
• Allelic frequency will be different to original population due to CHANCE