Lecture 8: The Evolution of Sex

Question 1

What is the definition of Outbreeding?

Answer 1

Outbreeding is the mating between individuals that are less related than the average relatedness in the same population, typically referring to matings between unrelated individuals

Question 2

What is the significance of Outbreeding?

Answer 2

Creates a greater average heterozygosity; more variation among offspring

Question 3

What is the definition of Inbreeding?

Answer 3

Inbreeding is the mating between individuals that are more closely related than the average relatedness in the same population, typically referring to matings between very closely related individuals

Question 4

What is the significance of Inbreeding?

Answer 4

Creates a greater average homozygosity; less variation among offspring

Increase in the % mortality of offspring because deleterious traits can become fixed

Question 5

Are most organisms sexual or asexual?

Answer 5

Sexual (undergo sexual selection at least on occasion)

Question 6

Describe the taxonomic distribution of asexual lineages?

Answer 6

Sporadic; asexual organisms are evolutionarily short-lived (i.e. become extinct)

Question 7

What is the definition of Cyclic Sexuality?

Answer 7

The cycling between sexual and asexual reproduction within an individuals lifecycle

Question 8

What is the significance of Cyclic Asexuality?

Answer 8

Being sexual/asexual during specific times can be advantageous (unstable conditions may require genetic variation)

Question 9

What does sex do?

Answer 9

Gene exchange and recombination through zygote formation/the formation of a temporary diploid stage

Question 10

How can recombination occur?

Answer 10

1. Crossing-over between homologous chromosomes during meiosis
2. Independent assortment of chromosomes during meiosis

Question 11

What is a consequence of recombination?

Answer 11

An increase in genetic variation/diversity between gametes and offspring

Question 12

What are the disadvantages to sexual reproduction?

Answer 12

1. Cost of meiosis (i.e. cost of producing males)
2. Need to find sexual partner
3. STDs
4. Mixing of female genes with mutated male genes
5. Breaking up co-adapted gene complexes

Question 13

What is the definition of the Cost of Meiosis?

Answer 13

The Cost of Meiosis is the 50% chance of elimination for any allele that codes for sexuality; the cost of producing males

Question 14

Why is asexual reproduction advantageous when looking at the Cost of Meiosis?

Answer 14

Asexual females have 2x the reproductive rates of sexual females because asexual females don’t waste resources on sons

Question 15

How do females poison their own, relatively unmuted genes with bad, mutated genes from males?

Answer 15

Most mutations arise from males and not females due to a greater number of meiotic divisions during spermatogenesis than oogenesis

Question 16

What are the advantages of sexual reproduction?

Answer 16

1. Faster elimination of deleterious mutations

2. Faster evolution (bringing favorable mutations together in the same individual)

Question 17

Describe the Muller’s Ratchet Model.

Answer 17

Asexual lineages accumulate deleterious mutations (i.e. mutational meltdown) and the least-mutated genotype is eventually lost for forever

Sexuality can restore the least-mutated genotype through recombination in a sexual population because the most-mutated genotypes are selected against

Question 18

Why does sex facilitate faster evolution than asexual reproduction?

Answer 18

In asexual populations, different colonies compete with one another (i.e. colonial interference)

Question 19

Did recombination arise originally as a mechanism for DNA repair?

Answer 19

The reason for the origin of sex (e.g. DNA repair) may have been different than the reasons for the maintenance of sex (e.g. faster evolution, elimination of deleterious alleles)

Question 20

What are the 2 principle ways of making gametes?

Answer 20

1. Few, large gametes

2. Many, small gametes

Question 21

What is the advantage to few, large gametes?

Answer 21

Increase in zygote survival/resources; high parental investment

Question 22

What is the advantage to many, small gametes?

Answer 22

High motility increases likelihood of pairing; low parental investment

Question 23

What is the definition of Anisogamy?

Answer 23

Anisogamy is the production of small and large gametes which coexist in the same population

Question 24

What is the significance of Isogamy?

Answer 24

Isogamy is the production of same sized gametes in the same population

Question 25

What is the female function in sex? The male function?

Answer 25

Female function: high reproductive effort

Male function: high mating effort

Question 26

What limits fitness for females? For males?

Answer 26

Female fitness: resources acquired

Male fitness: access to mates

Question 27

What type of selection is favored for gametes?

Answer 27

Disruptive selection

Question 28

What are the consequences of initial inequality?

Answer 28

1. Male-male competition (intra-sexual selection)

2. Female choice (inter-sexual section)

Question 29

Characteristics of the sex with high parental investment?

Answer 29

Choosey when selecting males (i.e female choice)

Question 30

Characteristics of the sex with low parental investment?

Answer 30

Will fight with other males for males (i.e. male-male competition)

Question 31

What is the definition of Sex-Role Reversal?

Answer 31

Sex-Role Reversal is the increase in paternal investment in each offspring