Unit 2 Lecture 10

Question 1

What do we mean by sex?

Answer 1

• Form of reproduction
• Existence of multiple sexes (e.g female and male)
• Mechanism of sperm transfer

All of these have evolutionary consequences

Question 2

What’s the alternative of sexual reproduction? Give examples

Answer 2

Asexual Reproduction
- Binary fission//fragmentation
- Budding
- Vegetative reproduction
- Sporogenesis (ferns)
- Parthenogenesis (animals)

Question 3

Which statement is true?
A. Sexual reproduction always happens between males and females
B. A species that reproduces sexually does not reproduce asexually
C. Once sexual reproduction evolves in a lineage, it doesn’t go back to sexual reproduction
D. All of the above
E. None of the above

Answer 3

E. None of the above

Question 4

Explain how this statement is false: Sexual reproduction always happens between males and females

Answer 4

Hermaphrodites: Sexual reproduction without two separate sexes, or each individual is both sexes

Question 5

Explain how this statement is false: A species that reproduce sexually does not reproduce asexually

Answer 5

Strawberry:
1.Sexual reproduction (pollination -> seeds) and Asexual reproduction (vegetative reproduction)
2. Bread mold
3. Aphids (sex and parthenogenesis)

Question 6

Explain how this statement is false: Once sexual reproduction evolves in a lineage, it doesn’t go back to asexual reproduction

Answer 6

Some lizards and snakes reproduce parthenogenetically

Question 7

What is parthenogenesis?

Answer 7

Parthenogenesis is when females will basically clone themselves and only make daughters (aphids)

Question 8

What is the “Two-fold Cost of Sex”?

Answer 8

• The asexual female can grow a bigger population faster because males cannot reproduce asexually (so they do not count)
• If you are a sexual female, 50% of your offspring will be male
• Main difference is how fast a population can grow between an asexual female and sexual female which is Calle Two-fold cost of sex

Question 9

What are the disadvantages of sex?

Answer 9

1. Search cost: have to search for mates
2. Reduced relatedness: offspring are only related to you by half
3. STD: might catch disease

Question 10

Name some advantages to sex

Answer 10

One female can potentially produce a huge amount of eggs which then changes the fitness benefit

Question 11

How can two-fold cost of sex be offset?

Answer 11

By having lots and lots of Abbies through sexual reporduction

Question 12

Name a big benefit to sexual reproduction

Answer 12

Recombination: chromosomes during meiosis will cross over and exchange segments of DNA

Question 13

What happens when there is asexual reproduction (no recombination)

Answer 13

• Consider a stretch of DNA undergoes a mutation; as a result one strand could have 2 beneficial mutations and 1 deleterious, and another could have 2 deleterious and 1 beneficial
• Through natural selection, they will select for the strands with 2 beneficial and 1 deleterious mutations

Because of this beneficial alleles increase, but also some deleterious alleles
- This is called “Muller’s Ratchet”: deleterious mutation accumulate in asexual populations because there is no recombination

Question 14

Explain what happens when there is sexual reproduction?

Answer 14

• Take the same two strands, through recombination they are able to make one strand with 2 deleterious, one strand with 2 beneficial, one strand with 3 deleterious, and one strand with 3 beneficial
• Through natural selection, they are able to select for the strand with 3 beneficial alleles

Question 15

What is considered NOT a benefit of sexual reproduction (recombination)

Answer 15

Recombination creates new beneficial alleles

Question 16

How does recombination help “clear deleterious alleles” exactly?

Answer 16

It exposes deleterious alleles to natural selection by removing its link to a beneficial allele

Question 17

Explain the different of frequency of deleterious mutations in sexual and asexual reproduction

Answer 17

• In asexual reproduction, deleterious mutations sometimes spread and reach fixation (100% frequency)
• In sexual reproduction, deleterious alleles never reach fixation; deleterious increased then were selected against to a very low frequency but didn’t drop to 0 due to recessive alleles

Question 18

Explain the red queen hypothesis

Answer 18

It is larger hypothesis about how evolution works and how organisms are adapted but not to the environment they live in (coined by levin baylon)
- Organisms are basically never adapted to the environment in which they live, they are adapted to the environment their parents live in
- The genes and traits they have is a result of natural selection that happened on their parents

Question 19

Explain how parasites cause evolution of sex reproduction

Answer 19

-The host frequency increases through time until it reaches some peak, at which point it is invaluable to the parasite, so the parasite frequency increases
- At this point, this host genotype is going to be selected against because of its infection of a parasite and will decrease till it reaches some midpoint
- Once the host starts to decrease, the parasite is going to decrease because it does not have as many hosts to infect

Question 20

The frequency of parasites and hosts cycle. Why?
A. Parasites grow abundant
B. Number of hosts is decimated
C. Parasites starve and decline
D. Hosts begin to recover
E. All of the above

Answer 20

E. All of the above

Question 21

What are the 3 basic principles of Red Queen?

Answer 21

1. Parasites evolve fast
2. Parasites that infect common host genotypes have higher fitness
3. Host individuals that can produce offspring with rare genotypes are more successful (because its going to be harder for the parasite to invade them)

Question 22

What is phenotypic plasticity?

Answer 22

The ability of individual genotypes to produce different phenotypes when exposed to different environmental conditions

Question 23

Name a real example of the red queen

Answer 23

Microphallus: a castrating parasite of freshwater snails
- Trematode worm that infects the New Zealand mud snail
- Orange cysts replace reproductive organs of snails

Parasites infect snails with a common genotype more easily than snails with rare genotype

Question 24

What does frequency-dependent selection mean?

Answer 24

The fitness of a phenotype depends on how common it is in the population