L5a and The Sex Paradox

why have sex?

what term has to do with disease resistance?

what happens in asexual populations? what is the term for this?

o   advantageous to switch up genes especially when selection changes over time or space

o   red-queen hypothesis: disease resistance

o   crossing over and recombination=more variation=more heterozygosity

o   muller’s ratchet: asexual populations, harmful mutations accumulate irreversibly because of genetic drift and mutation

how is sex determined?

what is it called when an organism can change sex from one to another?

what is the difference in size of male and female gametes called?

how do you get 2 different phenotypes?

o   sequential hermaphrodites: when an organism can change sex from male to female or female to male at some point in its life

o   anisogamy: difference in the size of male and female gametes

o   larger gametes=female, females by definition have higher parental investment

2 different phenotypes from hormones (SRY gene)

rule that says male reproductive success increases with multiple mates while female’s does not

organism that has both male and female reproductive organs

how do different chromosomes determine sex?

-              Bateman’s rule: male reproductive success increase with multiple mating while female reproductive success does not

-              Hermaphrodite: has both male and female reproductive organs or tissue

-              Genotypic sex determination: XX/XY and ZZ/ZW: different chromosomes. Ex: chickens

how do social mechanisms determine sex?

what is it called when a female is diploid and males are haploid?

what is it called when sex is based on environment?

-              Social sex determination:

o   In marine green spoon worm, if a larvae lands on a female, it develops into a male. If it grows alone, it becomes female

o   Ex: clownfish change sex based on dominance hierarchies

-              Haplodiploidy: females diploid, males haploid

-              Environmental sex determination: sex based on environment

o   Egg incubation affects sex development (high temp=female)

Weismann’s hypothesis

-              Sexual reproduction required finding a mate, passing on only half of genetics, and disrupting favorable gene combinations

-              Weismann’s hypothesis: sex enhances genetic variation=beneficial for adaptation

Fisher-muller hypothesis:

- Fisher-muller hypothesis: sex allows for faster spread of beneficial mutations

- Ex: yeast: in stable environments sex provides no advantage but in harsh conditions, sexual yeast adapts better