Evolution of Sex

Question 1

What is sex?

Answer 1

Recombination (the breakdown and bringing together of genetic materials) and reproduction.

Question 2

Sexual reproduction

Answer 2

The creation of a new genetic combination. Production of haploid gametes by meiosis, and fusion of these gametes to produce a zygote.
Sexual reproduction evolved from asexual reproduction.

Question 3

Asexual reproduction

Answer 3

Production of new individuals without a new genetic combination. (AKA parthenogenesis)
Example: whiptail lizard.

Question 4

The costs of sex

Answer 4

Cost of breaking up co-adapted gene complexes (if it ain’t broke, why fix it?)
Cost of making males (they can’t produce eggs)
Cost of STDs
Cost of finding a mate and mating (predation risk, time, energy)

Question 5

Why has sex evolved? (2 classes of theory)

Answer 5

1) Sex allows harmful mutations to be eliminated
2) Sex speeds up the rate at which adaptations can occur (genetic variation is also increased, which enhances the ability to adapt to changing environments)

Question 6

New Zealand Mud Snails…

Answer 6

• Can reproduce sexually and asexually
• Can be hosts of a parasitic worm

Question 7

The Two Sexes

Answer 7

Males – low gametic investment (make many small gametes, which are devoid of nutrients)
Females – high gametic investment (make few large gametes, which are nutritionally rich)

Question 8

Isogamy

Answer 8

Reproduction between equal sized gametes

Question 9

Evolution of Male and Female Gametes

Answer 9

Assumptions: a) trade-off between gamete size and number (many = smaller), b) zygote fitness increases with size
Competition to fertilize eggs led to disruptive selection on gamete size.
- Specializations in swimming (small) and providing energy (large)
- Selection against fusions between two small cells (not viable)
- Fusion between large cells rare and disadvantageous

Question 10

Anisogamy

Answer 10

Reproduction between gametes of different sizes