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7: Speciation

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    • Species: interbreeding group that are reproductively isolated through anatomy, ecology, behavior, or geographic distribution

    • Prezygotic barriers

      • Lack of mating access, prevent mating from being successful, prevent fertilization

    • Postzygotic barriers

      • Birth defects, infertility, hybrids that do not survive long or hybrids that are infertile

    • Speciation: development of a new species (through genetic divergence)

      • Mutation, genetic drift, and natural selection will produce genetic divergence 

      • Gene flow does not produce genetic divergence (alleles are mixed between multiple populations)

    • Reproductive isolation

      • Individuals in a population become isolated (geographic barrier, habitat, preferences, etc.) and do not breed

      • The isolated groups are affected by different evolutionary pressures → leads to changes in genetic traits

      • The isolated groups become different enough that they aren’t able to interbreed

      • The isolated groups would then be considered different species

    • Hybrids are partially reproductively isolated (process of speciation is happening, but full reproductive isolation hasn’t occurred)

      • Ex: mule (hybrid of a horse and donkey)

      • Sterile, generally don’t breed together in the wild

    • Note: species vs. subspecies

      • When dogs are bred together to create a new breed, the breed is considered a subspecies rather than a new species (new breed is still able to breed with other dogs)

    • The Hardy-Weinberg equation is a mathematical model used to predict the frequencies of alleles in a population.  

    • If a population is not evolving, it is considered to be in “Hardy-Weinberg equilibrium.”  

      • This means that the rate at which alleles are being inherited is not changing in the population...it is remaining the same.  

      • If the rate is changing, the population may be evolving (by processes such as natural selection, artificial selection, genetic drift, gene flow, etc.).

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    7: Speciation is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

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