1. Human Chromosomes 14.2

2. Sex-linked Gene Gene located on the X or Y chromosome.

3. Nondisjunction Error in meiosis in which homologous chromosomes fail to separate.

4. Key Concept Why are sex-linked disorders more common in males than in females? Males have just one X chromosome. Thus, all X-linked alleles are expressed in males, even if they are recessive.

5. Key Concept What is nondisjunction, and what problems does it cause? If nondisjunction occurs, abnormal numbers of chromosomes may find their way into gametes, and a disorder of chromosome numbers may result.