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Individuals of a natural population share morphological, physiological, and behavioral traits characteristic of the species. Alleles are the main basis of differences in the details of those shared traits. All alleles of all individuals in a population make up the population’s gene pool. An allele’s abundance in the gene pool is called its allele frequency. Microevolution is change in allele frequency. It is always occurring in natural populations because processes that drive it are always operating.

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Change in an allele’s frequency in a population.

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Abundance of a particular allele among members of a population.

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All the alleles of all the genes in a population; a pool of genetic resources.

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A mutation that has no effect on survival or reproduction.

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Mutation that alters phenotype so drastically that it causes death.

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Original source of new alleles

Large impact on populations

Unpredictable sequence

Average mutation rate predictable

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Sources of Variation Among Individuals of a Species

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Sources of Variation Among Individuals of a Species

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Share morphological, physiological, and behavioral traits because they have same genes

Traits vary a bit among members of sexually reproducing species

Variation arises mainly because different individuals inherit different combinations of alleles

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A group of organisms of the same species who live in a specific location and breed with one another more often than they breed with members of other populations.