Genetic Drift

As observed in Chapter 13, the Hardy-Weinberg law states that genes tend to remain at a constant frequency from generation to generation. However, by chance alone, genetic drift (a change in the genetic makeup of a population due to random events) may take place as a given gene fluctuates from its statistical average in any generation due to the

Figure 15.5 Some types of chromosomal changes that can occur. A. Deletion. Part of a chromosome breaks off and is lost. B. Translocation. Part of one chromosome becomes attached to another. C. Inversion. Parts of a chromosome breaks off, becomes inverted from its original position, and then is reattached.

Figure 15.5 Some types of chromosomal changes that can occur. A. Deletion. Part of a chromosome breaks off and is lost. B. Translocation. Part of one chromosome becomes attached to another. C. Inversion. Parts of a chromosome breaks off, becomes inverted from its original position, and then is reattached.

Evolution events that occur during meiosis and the production of gametes. In a large population, genetic drift is unlikely to make any significant difference. In a small population, however, the chance multiplications or failures to multiply of a single genotype may cause a marked change in its frequency and, in some cases, cause it to disappear altogether or, on the other hand, have a frequency of 100%. In other words, in a small population, the random shift in gene frequencies by chance may bring about evolutionary changes.

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