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Biol 121- 2010.03.17- Evolution- Variation in Populations and Mechanisms for Selection (Ch. 25).docx

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University of British Columbia
BIOL 121
Carol Pollock

Biol 121 225 Freeman 508511 Ch 25Mar 17 10 Variation in Populations and Mechanisms for Selection Why is variation good variation is usually good because if there is an environmental change there needs to be natural selection which requires genetic variation so that the species does not die out Geneticvariation refers to the number and relative frequency of alleles that are present in a particular population How is variation maintained in a 1 Sexual Reproduction population 4 2 Diploidy 3 Balanced polymorphismheterozygote advantage 4 Frequencydependent selection 1 1 Sexual reproduction in meiosis independent assortment as well as crossing over occur which contributes to variation in individuals 22 Diploidy2 alleles for every gene recessive alleles hide and are not expressed when there is a dominant allele both parents contribute an allele and both must give a recessive allele for there to be a recessive phenotype this means that having a recessive phenotype is less likely to occur which is a good thing if the recessive allele is bad 3 3 Balanced polymorphismheterozygote advantage polymorphism is when there are more than two phenotypes present can be due to multiple alleles incomplete dominance andor codominance heterozygote advantage means that individuals that are heterozygous have higher fitness than homozygous individuals results in balancing selectioneg a point mutatio
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