Evolution of Sex

Sexual reproduction

parents combine genetic info to form offspring

asexual reproduction

one parent copies itself to form offspring

sex

The combining and mixing of chromosomes during the formation of offspring. Involving two main processes:

• Meiosis halves the number of chromosomes during gamete formation

• Fertilization restores the original chromosome number as two gametes fuse to form a zygote

parthenogenesis

“virgin creation”
A form of asexual reproduction in which an embryo develops directly from an unfertilized egg cell without needing sperm.

hermaphrodite

an organism that posses both male and female reproductive organs, structures, or gametes.

twofold cost of sex

disadvantage of sexual reproduction is that it cuts the reproducing population in half.
2 parents=1 offspring.

muller’s ratchet

In asexual reproduction, deleterious mutations can continue to accumulate.

genetic load

burden placed on the fitness of the individual due to a deleterious mutation

red queen effect

when both the parasite and the host continuously evolve, but neither gains a lasting advantage, creating a cyclical pattern of evolution.

anisogamy

gametes that vary in size with in a species

operational sex ratio

Ratio of male to female availability for mating at any time.
Male-biased: more males are available for mating than females, so males have to outcompete each other.

Female-biased: more females than males are available for mating

sexual selection

A mechanism of evolution that favors traits increasing an organism's ability to successfully reproduce, even if those traits reduce individual survival.

intrasexual selection

competition between males in which they fight each other for access to females. Typically, the less limiting sex is males.

intersexual selection

When the limiting sex (usually females) discriminates among suitors of the other sex. Females choice.

direct benefits

Benefits that impact the female herself, provided by the male. food, protection, and care of offspring

indirect benefits

Benefits that enhance the quality of a female’s offspring, usually via favorable alleles passed to offspring.

arbitrary choice hypothesis

(Fisher’s Positive Feedback Cycle)

The process in which ornamental traits are favored even if the trait is not advantageous. This can cause it to evolve to such an extreme that it can outweigh the sexual advantage. (bright colors attract females but also predators)

• The idea that offspring will inherit mom's preferences but dad’s traits.

good gene hypothesis

females select mates with exaggerated or costly physical traits because those traits serve as honest signals of superior genetic quality, leading to higher-surviving or healthier offspring