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Lecture Set 2 Boag.docx

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Queen's University
BIOL 103
Peter T Boag

Lecture Set 2, week 7 Variation and Natural Selection in Population Key Terms for o Phenotype, genotype, locus, allele, dominant allele, recessive allele, Review homozygous, heterozygous o All populations of all species show phenotypic variation o Allows natural selection to work  variation Gene pool o Collection of all alleles at all loci in individuals in a population o Makes a random mating process all of the genetic variation can be Theoretical reassembled to a new set of zygotes for next generation concept o Most species of coral reproduce at particular times of year, they all release sperm and eggs at the same time like a gene pool literally o summed across thousands of loci, one individual has only a small fraction of the alleles present in an entire population o each diploid individual has a maximum of two different alleles at each locus, but additional alleles may exist at the same locus in other individuals Frequencies Phenotypes  physical expression of a genotype Genotype  combination of alleles at a given locus, on homologous chromosomes Alleles variants of DNAsequence at a given locus Variation o mutation causes ­ changes in DNAsequence, can be induced externally, alters DNAchemically to change sequence, cannot enter population unless in gametes germ cells ­ many mutations are repaired, most never show up in the gene pool, prokaryotes do not repair as well ­ efficiency of DNArepair effects net mutation rate. o sexual reproduction ­ in diploid, most important mechanism in large variation ­ meiosis shuffles maternal and paternal chromosomes ­ crossing over shuffles alleles into new combinations ­ results in genetic, phenotypic variation Variation o 3 chromosomes per haploid (n=3), 8 gamete types result from randomly grouped material and paternal chromosomes o diploid organism produces 2^n maternal and paternal chromosome combinations o n=23 in humans 2^23 Persistence of o biggest unsolved mystery in biolgy sexual o if you are a female who can reproduce asexually, and you environment is good reproduction you can pass 100% of genes onto offspring o sexual, has to give 50% contribution, they male could be better or not adapted o paradox , within 50 gens the asexual female would dominate the population
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