Chapter 19 - Introduction

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To fully appreciate this tutorial, you should be familiar with:
• Populations and population genetics
• The effects of nonrandom mating, mutation, genetic drift, gene flow, and natural selection on allele frequencies in populations
• The biological species concept

After this tutorial, you will be able to describe and give examples of:

• Prezygotic barriers

• temporal isolation
• habitat isolation
• behavioral isolation

• Postzygotic barriers

• hybrid inviability
• hybrid sterility
• hybrid breakdown

What prevents closely related species from interbreeding?

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Prezygotic barriers
Postzygotic barriers
Summary

The geographical ranges of lions and tigers overlap in certain parts of Asia, but a tiglion (a hybrid between a lion and a tiger) has never been found in nature. Lions and tigers do not interbreed in the wild but may do so in an artificial environment such as a circus.

Reproductive isolating mechanisms prevent two species whose ranges overlap from interbreeding. These barriers to gene flow are critical to the process of speciation, the evolution of new species. When a population becomes reproductively isolated from other members of the species, the gene pools of the two groups begin to diverge genetically. Over many generations, the differences that accumulate decrease the likelihood that members of the two groups will successfully mate and produce viable offspring. When no genetic exchange occurs between the population and its ancestral species, we say that speciation has occurred.