Sex

Question 1

Souces of Genotypic Variation

Answer 1

Sex

Question 2

Reduction of Variation

Answer 2

• Genetic Drift in finite populations
• Loss of alleles
• Loss of heterozygosity (Inbreeding)

Question 3

Sources of Allelic Variation

Answer 3

Mutations

Question 4

Heritable variation without changes in the genetic code

Answer 4

Epigenetic Inheritance

Question 5

Sex

Answer 5

• Shuffling of combinations of alleles
• No new alleles, only new genotypes

Question 6

What is Sex?

Answer 6

Meiosis with Crossing Over + Random Mating

Question 7

What happends during Sex?

Answer 7

• Meiosis (produce gametes)
• Random Mating (shuffling the gametes)

Question 8

What happends during Sex?
In Meiosis

Answer 8

Separates homologous chromosomes

Question 9

What happends during Sex?
In Random Mating

Answer 9

• Newly formed haploid chromosomes (sperm & eggs) come together
• Shuffling of allelic combinations into new genotypes

Question 10

Meiosis generates genotypic diversity in two ways:

Answer 10

(1) Physical exchange of homologous chromosomal regions
(2) Separation of homologous
chromosome pairs

Question 11

A process by which a molecule of nucleic acid (usually DNA, but can also be RNA) is broken and then joined to a different one

Answer 11

Genetic Recombination

Question 12

Pairing of homologous chromosomes

Answer 12

Synapsis

Question 13

Consequences of Sex

Answer 13

• Genetic Recombination (reduces LD)
• Random Mating (increases genotypic variation)

Question 14

Consequence of Sex
Genetic Recombination:

Answer 14

Mixes up combinations of alleles across loci (reduces Linkage Disequilibrium)

Question 15

Consequence of Sex
Random Mating:

Answer 15

• Mixes up combination of alleles at a given locus (increases genotypic variation
• can also help break up LD on different chromatids

Question 16

An important consequence of Eukaryotic Sex

Answer 16

• Meiosis
• Crossing over

Question 17

The non-random association of alleles at two or more loci, not necessarily on the same chromosome

Answer 17

Linkage Disequilibrium

Question 18

Linkage disequilibrium can be caused by ______

Answer 18

evolutionary factors such as natural selection and genetic drift

Question 19

_______ will break down linkage
disequilibrium on the ____ chromosome, and _____ _______ on ______ chromosomes

Answer 19

• Recombination
• same
• random mating
• different

Question 20

Why do we care about the LD?

Answer 20

• Useful to know which alleles are commonly associated with one another
• Patterns of LD can tell us about the evolutionary history of the population
• Breaking up LD will make a population respond more efficiently to the action of natural selection

Question 21

Random mating during SEX

Answer 21

• The haploid chromosomes (sperm and egg) come together
• Can get combination of favorable mutations more quickly
• Can remove unfavorable mutations more quickly

Question 22

Benefits of Sex
Genetic Recombination:

Answer 22

Breakdown of Linkage Disequilibrium

Question 23

Benefits of Sex
Random Mating:

Answer 23

• Increase genotypic diversity
• Bring together favorable mutations across loci
• Bring together unfavorable mutations across loci

Question 24

Bring together favorable mutations across loci

Answer 24

Create individuals free of deleterious mutations

Question 25

Bring together unfavorable mutations across loci

Answer 25

Deleterious combinations can be selected out of the population

Question 26

Cost of Sex

Answer 26

- Loss of Fitness relative to clonal populations - Reduces population growth rate by 1/2, because males cannot reproduce

Question 27

Sex is not ______

Answer 27

universal

Question 28

Sex occurs in ______, and not in ______ or ______

Answer 28

- Eukaryotes - Bacteria - Archaea

Question 29

It occurs often in plants, and in many invertebrates

Answer 29

Asexuality

Question 30

Some eukaryotes are asexual until they experience a large accumulation of ______ ______ (mutational meltdown) or _____, then they have sex

Answer 30

- deleterious mutations - stress

Question 31

Some eukaryotes have more than __ sexes (some ciliates have ___)

Answer 31

- 2 - 32

Question 32

Within Eukaryotes, sexual species tend to last ____

Answer 32

longer

Question 33

Asexual species are often ____ ____ ____ of novel habitats because of ___ ____ ____ (many ______ plants are asexual)

Answer 33

- good early colonizers - rapid growth rate - invasive

Question 34

In Eukaryotes, less than ___ are asexual

Answer 34

1%

Question 35

Summary Benefits of Sex

Answer 35

- Breakdown Linkage Disequilibrium - Increase in Genotypic Variation - Purge deleterious mutations more easily - Bring together favorable mutations - Evolution of “individuality”

Question 36

Summary Costs of Sex

Answer 36

- Lower Reproduction Rate (1/2) - Have to find mates (not all individuals reproduce) - Pass on only ½ of your genome at each reproduction event - Death of unique individuals (genome) in the parental generation