Chapter 15.3, Problem 6MI

Summary Introduction

To contrast:

Geographic isolation and reproductive isolation.

Introduction:

Hardy and Weinberg showed mathematically that evolution will not occur in a population unless allelic frequencies are acted upon by forces that cause change. When these forces are absent, the allelic frequencies remain the same and evolution does not occur. This idea came to be known as the Hardy- Weinberg principle.

Answer to Problem 6MI

Geographicisolationoccurs when a physical barrier separates a population. A new species can evolve when a population has been geographically isolated as they are unable to interbreed and exchange genes.

Reproductive isolation occurs when formerly interbreeding organisms can no longer mate and produce fertile offspring.

Explanation of Solution

Evolution of new species is called speciation. It occurs when members of similar populations do not interbreed to produce fertile offspring within their natural environment.

In nature physical barriers can break large populations into smaller populations. Sometimes new species may develop when members of a population are physically separated by a boundary. They cannot interbreed and exchange genes. Over time each small population might get adapted to its environment through natural selection and develop its own gene pool. This mechanism of speciation is called geographic isolation.

Speciation may occur when some members of a sexually reproducing population change so much that they can no longer produce fertile offspring with members of the original population. This mechanism that prevents gene flow among populations is called reproductive isolation.