Final

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Isogamy

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Isogamy refers to a form of sexual reproduction involving gametes of the same size. Since both gametes look alike, they cannot be classified as "male" or "female." Instead, organisms undergoing isogamy are said to have different mating types, most commonly noted as "+" and "-" strains. Fertilization occurs when "+" and "-" gametes fuse to form a zygote.

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anisogamy

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Anisogamy (also called heterogamy) refers to a form of sexual reproduction involving gametes of different sizes. The smaller gamete is considered to be male (sperm cell) whereas the larger gamete is regarded as female (egg cell).

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oogamy

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Oogamy is a form of anisogamy (heterogamy) in which the female gamete is significantly larger than the male gamete and non-motile (egg cell). The male gametes are typically highly motile spermatozoa competing for the fertilization of the immotile egg.

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Parthenogenesis

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is the growth and development of an embryo or seed without fertilization by a male. Parthenogenesis occurs naturally in some species, including lower plants, invertebrates (e.g. water fleas, aphids, some bees and parasitic wasps), and vertebrates (e.g. some reptiles,[1] fish, and, very rarely, birds[2] and sharks[3]). It is sometimes also used to describe reproduction modes in hermaphroditic species which can self-fertilize.

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Cost of producing males

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only female produce eggs so only 1/2 of sexual indivuals produce offsspring. sexual population has a lower reproduction rate.

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Heterogenesis and example

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reproducing both ways, e.g female aphids reproduce asexually by parthenogenesis in the summer but mate in seually prior to winter.

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Cost of meiosis

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sexual individuals only pass 1/2 of their genes to offspring =cost of meiosis.
this makes it clear that the cost of sex reduces fitness of indiviual

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Additional costs of sex

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1. Production of costly reproductive structures and secondary sexual traits
2.Mate searching, courtship, and aggressive behaviors are often time-
consuming, energetically costly, and can increase exposure to predators
3.Mate searching, courtship, and aggressive behaviors are often time-
consuming, energetically costly, and can increase exposure to predators

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Benefits of sex (group & individual)

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Sex shuffles genes and creates new
gene combinations in offspring
Sex can accelerate the rate of evolutionand also reduce the rate of
extinctionfor populations and species

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Kondrashov’s mutational theory

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Sex enhances the power of selection
against deleterious mutations, resulting in offspring of higher average fitness

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red queen hypothesis

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Sex creates new gene combinations,
which enables some offspring to persist in an ever-changing environment. kinda like arm race.

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Whiptail example

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Parthenogeneticwhiptails may recur
frequently through genetic anomalies
during hybridization, but not persist for
long relative to sexual parent species

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Muller’s ratchet

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Deleterious mutations
Deleterious mutations accumulate irreversibly
in asexual populations (the ratchet)
When the asexual line with the fewest
deleterious mutations is lost (by chance), you
cannotgo back (except by rare back-mutation)
Ratchet will be fast when...
Population size (N) is small (loss via drift)
Mutation rate (U) is high
Selection (s) is weak

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Mutational meltdown

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Müller’s ratchet causes mutational meltdown
Gradual loss of fitness due to increasing mutation load in asexual species
Loss of fitness –this is a cost that can accrue to an individual