Evolution and Sex I

Question 1

What are the two types of sexual systems?

Answer 1

Dioecious
Hermaphrodite

Question 2

What are the three dioecious mating systems?

Answer 2

Promiscuity
Polygamy
Monogamy

Question 3

What are the two hermaphrodite mating systems?

Answer 3

Outcrossing
Selfing

Question 4

What are the three components of sex?

Answer 4

Fertilization
Recombination
Segregation

Question 5

What is fertilization?

Answer 5

the union of two gametes to form a zygote, where one gamete is functionally male and the other functionally female

Question 6

What is recombination

Answer 6

Component of meiosis that alters the association among alleles at different loci on the same chromosome

Question 7

What is segregation?

Answer 7

affects how alleles associate at a single locus on separate homologous chromosomes

Question 8

What are the effects of recombination and segregation?

Answer 8

Gene shuffling

Question 9

How many of the components of sex must be lost for an organism to be asexual?

Answer 9

All three

Question 10

What is the paradox of sex?

Answer 10

Sex is the dominant mode of reproduction among eukaryotic organisms despite substantial costs associated with sex

Question 11

What are the three major costs of sex?

Answer 11

Cost of males
Cost of meiosis
Cost of sexual structures and behaviours

Question 12

What is meant by the cost of males?

Answer 12

o Sexual populations grow slower than asexual populations when everything else is the same between them other than their reproductive system
o In sexual populations with separate male and female sexes, only half of the individuals produce offspring
o In asexual populations all individuals produce offspring

Question 13

What is meant by the cost of meiosis?

Answer 13

Sexual genotypes pass on half the number of gene copies to each progeny compared to asexual genotypes, which pass on all of their gene copies to progeny

Question 14

What is meant by the cost of sexual structures and behaviours?

Answer 14

Sexual behaviour and structures are energetically costly, whereas asexual genotypes do not need to invest in sexual structures/behaviour

Question 15

What are the three major benefits of sex?

Answer 15

Male care
Purging deleterious alleles/Muller’s ratchet
Combining multiple beneficial alleles/Fisher-Muller Model of sex

Question 16

How is male care a benefit of sex?

Answer 16

o Male care can offset the cost of males

Question 17

Describe Muller’s ratchet.

Answer 17

Asexual populations accumulate deleterious mutations faster than sexual populations
There can never be fewer deleterious mutations in a population than the minimum number of mutations at the inception of that population
Each time a new mutation is fixed within the population by either selection or drift, it is another click in the ratchet, such that there is a gradual and unstoppable increase in mutation load that can only be purged via extinction

Question 18

What does Muller’s Ratchet lead to?

Answer 18

A mutational meltdown of asexual populations over time

Question 19

What does Muller’s Ratchet explain?

Answer 19

The maintenance of sex over long periods of time

Question 20

What does Muller’s Ratchet not explain?

Answer 20

Why asexual genotypes do not invade sexual populations

Question 21

What mechanisms enable Muller’s Ratchet to occur?

Answer 21

Recombination and segregation

Question 22

Describe the Fisher-Muller Model of Sex.

Answer 22

o In asexual individuals, beneficial and deleterious alleles get stuck in the same individuals
o Sex allows individuals to combine beneficial alleles and purge deleterious alleles
o F-M Model: Recombination and segregation in sexual genotypes allow individuals to combine multiple beneficial mutations into the same genome “quickly”, whereas asexual genotypes can only combine them through independent mutations “slowly”