5.4 notes Ch 24 - Group A5.4 Week Ch 23 Sexual Selection...

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Group A5.4 Week 09/07/09 – 09/11/09 Ch 23 Sexual Selection - Can result from sexual dimorphism, which are the difference between the sexes in secondary sexual characteristics - Intrasexual Selection – Selection within the same sex; individuals compete directly for mates of the opposite sex. Example: single male patrols a group of females, preventing other males from mating with them. - Intersexual Selection – Individuals (usually females) are choosy in selecting mate. Example: female choice depends on male’s appearance or behavior Preservation of Genetic Variation - Various mechanisms help preserve genetic variation in a population o Diploidy – Maintains genetic variation with hidden recessive alleles o Balancing Selection – Occurs when natural selection maintains stable frequencies of 2 or more phenotypic forms. o Heterozygote Advantage – Heterozygotes have higher fitness than homozygotes. Natural selection will tend to maintain 2 or more alleles at locus. Ex: Sickle cell allele o Frequency Dependent Selection – Fitness of one phenotype declines if it becomes too common in population. Selection then favors other selection.
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