Biology | Answers to Review Questions

Author Dr. George B. Johnson, Washington University
Author Dr. Peter H. Raven, Missouri Botanical Gardens & Washington University
Contributor Dr. Susan Singer, Carleton College
Contributor Dr. Jonathan Losos, Washington University

Answers to Review Questions

Chapter 13 (p. 274)

1. Recognition of the significance of Koelreuter's theories was delayed because subsequent workers for almost a century did not quantify their results.

2. In the garden pea, segregation is seen among the offspring. A large number of true-breeding varieties were available. They were small, easy to grow, and have a short generation time. The pea flowers also have both male and female organs enclosed within the same flower, allowing Mendel to permit self-fertilization or to cross-fertilize them.

3. To determine an unknown genotype, cross the plant with a homozygous recessive (white) plant. If the unknown plant was homozygous (WW) for the purple color, 100% of the offspring will also be purple.

4. 1/16 should be homozygous recessive for both traits.

5. Its frequency is maintained because the physiological effects are not evident until relatively late in life, generally after some offspring have already been reproduced.

6. In Morgan's experiment the female had one chromosome with the red eye gene and one with the gene for white eyes. The male had the red-eyed gene on its X chromosome. Its other chromosome was Y. All females would receive at least one gene for red eyes. Half of the males would have the red-eyed gene and half would have the white-eyed gene. The Y chromosome has no gene for eye color, so whatever gene is carried on the X chromosome prevails. Though half of the males would have red eyes, all of the white-eyed flies would be males.

7. Primary nondisjunction is the failure of chromosomes to separate from one another in meiosis. Down syndrome is usually caused by primary nondisjunction.

8. The genotype of a person with Klinefelter syndrome is XXY, which makes him genetically male, since the presence of the Y-chromosome determines maleness. The individual appears female.