Why Sex? Flashcards
1
Q
why sex?
A
sex is dangerous, complicated, and costly
2
Q
skipping sex is an option
A
parthenogenesis
3
Q
sex
A
- the means by which two individuals are combined to produce an offspring
- each parent contributes a gamate
4
Q
gamete
A
- reproductive cell, usually an egg or a sperm
- gametes possess half as much DNA as the tissue cells
5
Q
egg (ovum)
A
- in sexually reproducing organisms, the gamete that belongs to females
- the larger of the gametes & is nonmotile
6
Q
sperm
A
- gamete that belongs to males
- the smaller of the gametes & in motilem
7
Q
motile
A
swims using a flagella
8
Q
two-fold cost of sex
A
- the production of males in a population reduces its reproductive potential by a factor of 2
- the higher growth rate of asexual individual means that they should quickly come to dominate a population, all else being equal
9
Q
passing on DNA
A
- eggs & sperm contain 50% of an individuals DNA
- parthenogenetic females pass on 100% of their DNA
10
Q
Muller’s Ratchet
A
a cost of forgoing sex
11
Q
a cost of forgoing sex
A
- an asexual individual will pass on all of her mutations, including the deleterious mutations
- deleterious mutations will accumulate
- the accumulation of mutations in a population is a form of genetic load
12
Q
genetic load
A
a reduction in the mean fitness of a population
13
Q
sex breaks Muller’s ratchet. how?
A
recombination
14
Q
recombination
A
- allows a population tp purge deleterious alleles
- the no-mutation group can be reconstituted by recombination
15
Q
facultative parthenogenesis
A
- aphids are all female in the summer, sexual in the fall
- eggs overwinter, & a new generation of parthenogenetic females is born in the spring
- female aphid giving birth to a daughter by parthenogenesis
