1. Chapter 14 Test Prep

2. _____ 2. If the allele for having a white forelock is dominant, family members WITHOUT a white forelock are a. homozygous recessive. b. homozygous dominant. c. heterozygous. d. trisomal

3. Which of the following diseases and conditions does not appear until late in a person’s life? a. cystic fibrosis b. colorblindness c. sickle cell disease d. Huntington disease

4. Why are all X-linked alleles expressed in males, even if they are recessive?

5. What percentage of human sperm cells carry an X chromosome? a. 0% b. 50% c. 25% d. 100%

6. How many generations are shown in Figure 14– 2? a. 2 b. 4 c. 6 d. 8

7. A man who is not colorblind and a woman who is a carrier of the disorder have a son. What is the probability that their son will be colorblind?

8. If nondisjunction occurs during meiosis, a. only two gametes may form instead of four. b. some gametes may have an extra copy of some genes. c. the gamete cannot join another to form an organism. d. the gametes redistribute chromosomes after meiosis.

9. _____ 1. Colorblindness is more common in males than in females because a. the allele for colorblindness is dominant and located on the X chromosome. b. the allele for colorblindness is recessive and located on the Y chromosome. c. the allele for colorblindness is recessive and located on the X chromosome. d. the allele for colorblindness is recessive and located on the Y chromosome.

10. . If malaria were eliminated from a certain area, how do you think the frequency of the sickle cell allele in that area would change? Explain.

11. Which of the following combinations of sex chromosomes represents a female? a. XY b. XXXY c. XXY d. XX

12. People who are heterozygous for sickle cell disease are generally healthy because they a. are resistant to many different diseases. b. have some normal hemoglobin in their red blood cells. c. are not affected by the gene until they are elderly. d. produce more hemoglobin than they need.

13. Why is a person who has the genotype XXY a male, even though he has two X chromosomes in his cells?

14. Which of the following pairs of genotypes result in the same phenotype? a. I A I A and I A I B b. I B I B and I A I B c. I B I B and I B i d. I B i and ii

15. The allele for the presence of a white forelock is dominant in Figure 14–1. What is the probability of the couple labeled 2 of having a child with the trait? a. 25%c. 75% b. 50%d. 100%

16. How many chromosomes are shown in a normal human karyotype? a. 2 b. 44 c. 23 d. 46

17. Which of the following statements is true? a. Females cannot have hemophilia. b. A colorblind boy’s mother must carry the gene for colorblindness. c. A sex-linked allele cannot be dominant. d. A colorblind boy’s father must carry the gene for colorblindness.