Genetics For Dummies, 3rd Edition

Chapter 4

Law Enforcement: Mendel’s Laws Applied to Complex Traits

IN THIS CHAPTER

Examining the variations of dominant alleles

Reviewing how simple inheritance becomes more complicated

Looking at some exceptions to Mendel’s laws

Although nearly 150 years have elapsed since Gregor Mendel cultivated his pea plants (introduced in Chapter 3), the observations he made and the conclusions he drew still accurately describe how genes are passed from parent to offspring. The basic laws of inheritance — dominance, segregation, and independent assortment — continue to stand the test of time.

However, inheritance isn’t nearly as simple as Mendel’s experiments suggest. Dominant alleles don’t always dominate, and genes aren’t always inherited independently. Some genes mask their appearances, and some alleles can kill. This chapter explains exactly how Mendel was right, and wrong, about the laws of inheritance and how they’re enforced.

Dominant Alleles Rule … Sometimes

If Mendel had chosen a plant other than the pea plant for his experiments, he may have come to some very different conclusions. The traits that Mendel studied show simple dominance — when the dominant allele’s phenotype, or ...