Textbook Notes (368,123)
Canada (161,661)
Biology (310)
BIOL 359 (43)
Chapter 8

Chapter 8.docx

2 Pages
132 Views
Unlock Document

Department
Biology
Course
BIOL 359
Professor
Jonathan Witt
Semester
Winter

Description
Chapter 8: Evolution at Multiple Loci: Linkage and Sex 8.3. The Adaptive Significance of Sex - Many species are capable of both sexual & asexual reproduction o Parthenogenesis: Offspring develop from unfertilized egg, no male participation, females produce live-born genetically identical to themselves - Which Reproduction Mode is Better: Sexual or Asexual? o The null model for population that reproduces sexually and asexually  1. Female’s reproductive mode does not affect the # of offspring  2. Female’s reproductive mode does not affect the probability of offspring survival o Asexual females produce 2x as many grandchildren as sexual females  Constitute larger fraction of the population every generation, population destined to be overwhelmed by asexuals  However, asexual takeovers do not seem to have happened very often  Null model is violated o 1. The # of offspring varies depend on whether the female is sexual or asexual  Fathers provide resources or other forms of parental care in minority of species, majority just provide genes o 2. The probability of survival does depend on whether she produces them asexually or sexually  E.g. Flour beetles - 2 strains: Red = Sexual & Black = Asexual  Not capable of asexual reproduction, for the asexual strain, each generation # was counted, and replaced each 1 of the black adults with 3 new black adults from a reservoir population (no competition)  Black strain with 3x reproductive success than the red strain, but there is no adaptation  no evolution  Red adults breed among themselves  evolution  Environmental selection: Spiked flours with malathion o 8 replications with different malathion concentrations  Population was prevented from mating with each other & kept for 30 generations o Asexual strain produce more offspring than sexual strain, so the only way asexual would fail to take over is if the second assumption is incorrect  Control: Neither population was allowed to evolve, but black strain has 3x reproductive advantage over the red strains o Black strain quickly eliminated the red strain  Experimental: Initially the black strain appears to be taking over, but the evolving red strain recovered & completely eliminated the black strain at the end o The speed elimination took over depends on the malathion concentration  High malathion concentration: Stronger selection for insecticide resistance, greater advantage for sexual reproduction, faster - Sex in Populations Means Genetic Recombination o Sex: Reproduction involving meiosis “crossing-over” and mating between unrelated individuals  Every generation, allele will be part of a different multilocus genotype  E.g. Artificial selection increases the rate of recombination o Genetic recombination reduces linage disequilibrium through shuffling of multilocus genotypes  In a population in linkage equilibrium, ,sex has no effect, thus no benefits - Genetic Drift, in Combination with Mutation, can Make Sex Beneficial o The removal of a deleterious mutation can be through back, counter mutation or by mating with an individual with no deleterious mutations o Muller’s ratchet: Asexual populations are doomed to accumulate deleterious mutations  Sex breaks the ratchet, mutations can be quickly reconstituted by outcrossing &
More Less

Related notes for BIOL 359

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit