Topic 1 Evolution: Maintaining Reproductive Isolation

Question 1

• There are multiple ways to prevent gene flow, and they can be categorized into prezygotic or postzygotic isolation

Answer 1

Note

Question 2

• This type of isolation prevents fertilization before mating is attempted, and so a zygote is not formed.

Answer 2

Prezygotic Isolation

Question 3

1. Habitat Isolation
2. Temporal Isolation
3. Behavioral Isolation
4. Mechanical Isolation
5. Gametic Isolation

Answer 3

Types of Prezygotic Isolation

Question 4

• Species do not encounter each other because they live in different habitats, even if they live in the same geographical area

Answer 4

1. Habitat Isolation

Question 5

• Species reproduce at different seasons/times

Answer 5

2. Temporal Isolation

Question 6

• Some species will not reproduce with each other if they do not perform the correct courtship rituals

Answer 6

3. Behavioral Isolation

Question 7

• Occurs when male and female genitalia are not compatible

Answer 7

4. Mechanical Isolation

Question 8

• Male and female gametes do not recognize each other. The male gametes also may not survive in the environment of the female gametes

Answer 8

5. Gametic Isolation

Question 9

• Speciation can happen when two populations live in different habitats. The habitats do not need to be far apart. The two cricket species can live in close proximity, but because of their different soil preferences, they became genetically isolated

Answer 9

Note

Question 10

• The shape of the male reproductive organ varies in male damselfly species, and it is only compatible with the female of that species. Because of the reproductive organ incompatibility, the species are kept reproductively isolated

Answer 10

Note

Question 11

• If a zygote does form, there are postzygotic methods to maintain reproductive isolation

Answer 11

Postzygotic Isolation

Question 12

1. Hybrid Inviability
2. Hybrid Sterility
3. Hybrid Breakdown

Answer 12

Postzygotic Isolation

Question 13

• The zygote fails to develop properly and dies before reaching reproductive maturity

Answer 13

1. Hybrid Inviability

Question 14

• Hybrids become functional adults but cannot reproduce

Answer 14

2. Hybrid Sterility

Question 15

• Hybrids produce offspring that have reduced viability/ fertility. The hybrid’s children cannot reproduce

Answer 15

3. Hybrid Breakdown

Question 16

• Mules are hybrids formed from a cross between a horse and a donkey. The resulting offspring, mules, usually have hybrid sterility because of the difference in the number of chromosomes between the parent species

Answer 16

Note