Isolation And Speciation

Question 1

Define speciation

Answer 1

When two groups of organisms can no longer breed together to produce fertile offspring and are therefore 2 different species.

Question 2

Define allopatric speciation.

Answer 2

When populations that once interbred become separated geographically into 2 groups.

Question 3

Define a deme

Answer 3

Local populations that interbreed and share a distinct gene pool.

Question 4

Define sympatric speciation

Answer 4

Speciation that arises from different forms of isolation and when they share a habitat.

Question 5

How do the gene pools of demes alter?

Answer 5

1. Variation in both demes
2. Selection pressures leads to alleles w selective advantage. Selection pressures different for demes so alleles are different
3. Organisms with selective advantage survive and pass on advantageous alleles
4. Repeated many times
5. Eventually genes of organisms from two populations become so different that even if animals could interbreed and produce offspring the homologous chromosomes would become so different they wouldn’t be able to pair up and would be infertile.

Question 6

What are the 5 types of pre-zygotic isolation?

Answer 6

Geographical
Behavioural
Morphological
Gametic 
Seasonal

Question 7

What is geographical isolation?

Answer 7

When a physical barrier separates demes and the genes of them alter.

Question 8

What is behavioural isolation?

Answer 8

Variations in courtship and mating behaviour can lead to groups of particular species becoming isolated from each other.

Question 9

What is seasonal isolation?

Answer 9

Reproductive organs mature at different times of the year so organisms aren’t able to interbreed

Question 10

What is gametic isolation?

Answer 10

Although the gametes of two different organisms have the potential to meet, fertilisation doesn’t occur. For example if the sperm can’t survive in the oviduct.

Question 11

What is morphological isolation?

Answer 11

Variation in the sexual organs of organisms of the same species can lead to them not being able to mate successfully.

Question 12

What are 3 types of post - zygotic isolation?

Answer 12

Hybrid inviability
Hybrid sterility
Hybrid breakdown

Question 13

What is hybrid inviability?

Answer 13

Fertilisation occurs but the embryo is not able to develop into a living organism

Question 14

What is hybrid sterility?

Answer 14

A hybrid organism is formed but it is sterile. This is because it’s homologous chromosomes can’t pair up during meiosis 1 so gametes can’t form.

Question 15

What is hybrid breakdown?

Answer 15

Some F1 hybrids are sterile but the F2 aren’t.