Lecture VI - Sex and Sexual Selection

Lecture VI - Sex and Sexual Selection - Lecture VI Sex and...

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Unformatted text preview: Lecture VI Sex and Sexual Selection Sexual Reproduction - Review Occurs in two stages: 1. Creation of gametes by separation of the chromosomal pairs (gametogenesis) 2. Creation of a new organism by fusion of two gametes (fertilization) http://upload.wikimedia.org/wikipedia/en/7/75/Meiosis.jpg http://www.monteweston.com/Biology/Bio/collfontcolor.jpg Recombination The two halved of the genome of an individual is inherited from its two parents However, the gametes produced by that individual usually differ drastically from those that created its own genome. This is due to the process of recombination Recombination B Recombination occurs at two levels: Chromosomal during meiosis chromosomes assort independently of one another. During meiosis chromosomes of homologous pairs dont have any particular affinity with other chromosomes from the same gametic source Between homologs at the early stages of meiosis, homologous chromosomes exchange parts of their DNA Recombination C Recombination by exchange of genetic material http://www.estrellamountain.edu/faculty/farabee/biobk/Crossover.gif Recombination by independent assortment http://www.estrellamountain.edu/faculty/farabee/biobk/meiosis3.gif Disadvantages of Sex For both: Same investment, the genetic fitness Cannot reproduce without another individual, i.e., must convince another individual to breed This activity reduces investment in other activities Genetic material must be removed from interior of body Possibilities of combining with alleles with reduced fitness Disadvantages of Sex For females: Parasitism by male half of genome: same () genetic fitness, much larger investment http://flatrock.org.nz/topics/men/assets/sperm_egg_summit2.jpg Is Sex Universal? Short answer no Most single-celled organisms do not have sex (4 of the 7 Kingdoms) Many parthenogenic species among multicellular plants/animals These species are, essentially, clone lines of females So, Why Sex? What are, therefore, the advantages of sex? Increased variability among offspring Increased rate of spread of beneficial mutations Increased rate of evolutionary response to environment Reduced effects of deleterious alleles http://animals.timduru.org/dirlist/snake/rep_s011-MalagasyGiantHognoseSnakes-Interwinded-Mating.jpg http://drake.marin.k12.ca.us/academics/seadisc/ES%20Projects/arroyo%20toad2/images/sex.jpg http://www.hr-rna.com/RNA/images/Other%20Insects/Tigers/Tigers%20splend%20mating.jpg Increased Variability Among Offspring Because of the randomness of recombination, offspring often differ substantially This has multiple benefits, two major ones: Reduced sibling competition Increased probability that an individual will survive in a heterogeneous environment http://tgrc.ucdavis.edu/images/83L5318-LA1656-pen-low.jpg http://www.osha.igs.net/~kiddbatt/DOCS/graphics/discussion/kitangel1.jpg Increased Rate of Spread of Beneficial...
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Lecture VI - Sex and Sexual Selection - Lecture VI Sex and...

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