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pathenogenesis
virgin birth - identical clones from females with no male contribution
obligate parthenogenesis
entire species consists of females only, which reproduce by making identical clones of themselves
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
hermaphrodites
organisms that have both male and female sex organs and are capable of self fertilization
the offspring of hermaphrodites are genetically
less diverse than the offspring of individuals that outcross
maynard smith model assumptions
a female’s reproductive mode does not affect the number of offspring that she can make
a female’s reproductive mode does not affec tthe probability that her offspring will survive
outcrossing results in new combinations of
genes in the offspring
recombination crossing over in the process of meiosis during gametogenesis
creates new gentic variance
two factors create genetically diverse offspring and
they allow for the purging of deleterious mutations
self fertilization is still a form of sexual reproduction because
chromosomal crossing over and recombination cna still occur during gametogenesis
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
outcrossing results in
increased fitness, and the outcrossing rate itself can increase in response to stress
crossing over and recombination during gametogenesis is a very important component of sexual reproduction, and has two important effects
it breaks down linkage disequilibrium
it increases genetic diversity in offspring by creating new combinations of alleles
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
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)
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
linked
if genes are located close together on the same chromosome
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
benefits of recombination during meiosis
breaks up linked genes and breaks down linkage disequilibrium
sexual recombination creates new
combinations of alleles and destroys existing combinations
the point is that with recombination
you will always ahce at least some of the favourable genotypes
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
sex is beneficial indefinitely in
situations where the environment is continuously change