Exploring Complex Inheritance Patterns and Gene-Environment Interactions

1. Section 4: Beyond Mendelian Heredity Preview • Bellringer • Key Ideas • Many Genes, Many Alleles • Genes Affected by the Environment • Genes Linked Within Chromosomes • Summary

2. Bellringer Study the animals shown in Figure 11. List possible mechanisms that allow the arctic fox to change its fur color with changing seasons.

3. Key Ideas • Are there exceptions to the simple Mendelian pattern of inheritance? • How do heredity and the environment interact to influence phenotype? • How do linked genes affect chromosome assortment and crossover during meiosis?

4. Many Genes, Many Alleles • Most patterns of inheritance are more complex than those that Mendel identified. • The Mendelian inheritance pattern is rare in nature; other patterns include polygenic inheritance, incomplete dominance, multiple alleles, and codominance. • A character that is influenced or affected by more than one gene is called a polygenic character. • Eye color, height, and skin color are examples of polygenic characters. Most characters are polygenic.

5. Many Genes, Many Alleles, continued • Genes that have three or more possible alleles are said to have multiple alleles. • Multiple alleles control the ABO blood groups (blood types) in humans. • Codominance is a condition in which both alleles for the same gene are fully expressed. • The genetics of human blood groups is an example of codominance.

6. Blood Phenotypes

7. Visual Concept: Comparing Complete, Incomplete, and Codominance

8. Genes Affected by the Environment • Phenotype can be affected by conditions in the environment, such as nutrients and temperature. • In humans, many characters that are partly determined by heredity, such as height, are also affected by the environment. • Many aspects of human personality and behavior are strongly affected by the environment, but genes also play an important role.

9. Genes Linked Within Chromosomes • Many traits do not follow Mendel’s laws because he studied the simplest kinds of heredity where characters are determined by independent genes. • During meiosis, genes that are close together on the same chromosome are less likely to be separated than genes that are far apart. • Genes that are close together, as well as the traits they determine, are said to be linked. • Linked genes tend to be inherited together.

10. Summary • The Mendelian inheritance pattern is rare in nature; other patterns include polygenic inheritance, incomplete dominance, multiple alleles, and codominance. • Phenotype can be affected by conditions in the environment, such as nutrients and temperature. • During meiosis, genes that are close together on the same chromosome are less likely to be separated than genes that are far apart.