Module 8: Evolution and Sexual Reproduction

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23 Terms

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pathenogenesis

virgin birth - identical clones from females with no male contribution

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obligate parthenogenesis

entire species consists of females only, which reproduce by making identical clones of themselves

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cyclical parthenogenesis

populations consist of females that reproduce clonally throughout most of the year, but at certain times, males are produced and sexual reproduction occurs

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hermaphrodites

organisms that have both male and female sex organs and are capable of self fertilization

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the offspring of hermaphrodites are genetically

less diverse than the offspring of individuals that outcross

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maynard smith model assumptions

  1. a female’s reproductive mode does not affect the number of offspring that she can make

  2. a female’s reproductive mode does not affec tthe probability that her offspring will survive

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outcrossing results in new combinations of

genes in the offspring

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recombination crossing over in the process of meiosis during gametogenesis

creates new gentic variance

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two factors create genetically diverse offspring and

they allow for the purging of deleterious mutations

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self fertilization is still a form of sexual reproduction because

chromosomal crossing over and recombination cna still occur during gametogenesis

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the offspring resulting from self-fertilization are

genetically less diverse than normal sexual reproduction involving outcrossing, because of the loss of diversity resulting from mating between different individuals

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outcrossing results in

increased fitness, and the outcrossing rate itself can increase in response to stress

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crossing over and recombination during gametogenesis is a very important component of sexual reproduction, and has two important effects

  1. it breaks down linkage disequilibrium

  2. it increases genetic diversity in offspring by creating new combinations of alleles

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linkage disequilibrium constitutes a violation of Mendel’s second law

it can be defined as non-random associations between alleles at different loci, it can arise when different loci are situated close together on the same chromosome, resulting in them being inherited as a single unit, instead of segregating independently, this will result in less genetic diversity in offspring

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  1. first law: random segregation

alleles at a single locus segregate randomly, offspring have a 50% chance of inheriting each of a parent’s alleles (this is the basis of the hardy-weinberg principle)

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  1. second law: independent segregation

alleles at different loci segregate independently, so that the inheritance of alleles at locus A is independent of the inheritance of alleles at locus B

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linked

if genes are located close together on the same chromosome

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linkage disequilibrium

linked genes dont segregate independently, but inherited as a single unit, the genotypes at two different linked loci will not be randomly associated with each other

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benefits of recombination during meiosis

breaks up linked genes and breaks down linkage disequilibrium

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sexual recombination creates new

combinations of alleles and destroys existing combinations

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the point is that with recombination

you will always ahce at least some of the favourable genotypes

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Red Queen hypothesis

host/parasite and predator/prey dynamics: both must continually evolve better means for coping with the other. Sex is adaptive in such circumstances because it provides new and/or different allelic combinations across loci

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sex is beneficial indefinitely in

situations where the environment is continuously change