Chapter 13 - Answers to End-of-Chapter Questions


1. The law of segregation states that inherited elements separate during meiosis and that the individual receives one copy from each parent. The law of independent assortment states that traits on different chromosomes are inherited independently. During meiosis, four haploid cells are formed, each having a complete single set of chromosomes. The members of each pair are independent.

2. Genotype is what the genes are, phenotype is the expression of the genes. Homozygote implies two identical alleles; heterozygote implies two different alleles. Wild type occurs in the natural state; mutant is the changed state. Dominant is expressed if present; recessive is expressed only if dominant is not present.

3. One answer: For the autosomal recessive, neither parent of the person exhibiting the trait need have the condition. For an autosomal dominant, one or both parents of the person exhibiting the trait will also exhibit the condition.

4. A possible partial pedigree can be found on the next page. Key -- page 270.

5. 1 in 4

6a. Phenotype: All tall; Genotype: Tt
b. Phenotype: All tall; Genotype 1/2 TT, 1/2 Tt
c. Phenotype: 1/2 tall; Genotype 1/2 Tt, 1/2 tt

7a. 100%
b. 1/2 for each trait for mother; 1/2 for each trait for father. Regarding probability or Punnett Square, answers will vary.

8. Answers will vary. Many close marriages.

9a. Could be either epistasis or polygenetic inheritance.
b. Phenocopy

10. 1 in 3

11. Definitions in text.

12. Type B = 1/2
Type AB = 0
Type O = 0

13. Check in text definitions.

14a. Dominant = white feathers and large comb; recessive = dark feathers and small comb b. 3/16

15. Epistasis

16. Definitions in text.

17. Ll Mm Pdpd

18. Homozygous dominant is lethal. Therefore, 1/4 of pups died. (For a numerical comparison, see page 262.)

19. Multifactorial inheritance or epistasis.


1. Genes on the same chromosome are inherited as a unit -- unless crossing over occurs.

2. Answers will vary.

3. Multifactorial inheritance. See Table 13.7.

4. Answers will vary.

5. If the recessive lethals don't match, no one will know. If the recessive lethals do match, the chances are still only 1/4 that the appropriate two sets of chromosomes will get together. If the recessive lethals do match and the lethality prevents any development, the couple would never know about the potential baby.

6. Tay-Sachs is recessive.

7. If a dominant is present, it will be expressed.

8. Recessive. Back to the Punnett Square.


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