Mendel and the Gene Idea

1. Chapter 14 Mendel and the Gene Idea Questions prepared by Janet LanzaUniversity of Arkansas at Little Rock Louise PaquinMcDaniel College

2. Independent AssortmentImagine crossing a pea heterozygous at the loci for flower color (white versus purple) and seed color (yellow versus green) with a second pea homozygous for flower color (white) and seed color (yellow). What types of gametes will the first pea produce? • two gamete types: white/white and purple/purple • two gamete types: white/yellow and purple/green • four gamete types: white/yellow, white/green, purple/yellow, purple/green • four gamete types: white/purple, yellow/green,white/white, and purple/purple • one gamete type: white/purple/yellow/green

3. Pea plants were particularly well suited for use in Mendel's breeding experiments for all of the following reasons except that • peas show easily observed variations in a number of characters, such as pea shape and flower color. • it is possible to control matings between different pea plants. • it is possible to obtain large numbers of progeny from any given cross. • peas have an unusually long generation time. • many of the observable characters that vary in pea plants are controlled by single genes.

4. A cross between homozygous purple-flowered and homozygous white-flowered pea plants results in offspring with purple flowers. This demonstrates • the blending model of genetics. • true-breeding. • dominance. • a dihybrid cross. • the mistakes made by Mendel.

5. Imagine a genetic counselor working with a couple who have just had a child who is suffering from Tay-Sachs disease. Neither parent has Tay-Sachs, nor does anyone in their families. Which of the following statements should this counselor make to this couple? • “Because no one in either of your families has Tay-Sachs, you are not likely to have another baby with Tay-Sachs. You can safely have another child.” • “Because you have had one child with Tay-Sachs, you must each carry the allele. Any child you have has a 50% chance of having the disease.” • “Because you have had one child with Tay-Sachs, you must each carry the allele. Any child you have has a 25% chance of having the disease.” • “Because you have had one child with Tay-Sachs, you must both carry the allele. However, since the chance of having an affected child is 25%, you may safely have thee more children without worrying about having another child with Tay-Sachs.” • “You must both be tested to see who is a carrier of the Tay-Sachs allele.”

6. Albinism in humans occurs when both alleles at a locus produce defective enzymes in the biochemical pathway leading to melanin. Given that heterozygotes are normally pigmented, which of the following statements is/are correct? • One normal allele produces as much melanin as two normal alleles. • Each defective allele produces a little bit of melanin. • Two normal alleles are needed for normal melanin production. • The two alleles are codominant. • The amount of sunlight will not affect skin color of heterozygotes.

7. Imagine that the last step in a biochemical pathway to the red skin pigment of an apple is catalyzed by enzyme X, which changes compound C to compound D. If an effective enzyme is present, compound D is formed and the apple skin is red. However, if the enzyme is not effective, only compound C is present and the skin is yellow. Thinking about enzyme action, what can you accurately say about a heterozygote with one allele for an effective enzyme X and one allele for an ineffective enzyme X? • The phenotype will probably be yellow but cannot be red. • The phenotype will probably be red but cannot be yellow. • The phenotype will be a yellowish red. • The phenotype will be either yellow or red. • The phenotype will be either yellowish red or red.

8. In humans, alleles for dark hair are genetically dominant, while alleles for light hair are recessive. Which of the following statements is/are most likely to be correct? • Dark hair alleles are more common than light hair alleles in all areas of Europe. • Dark hair alleles are more common than light hair alleles in southern Europe but not in northern Europe. • Dark hair alleles are equally common in all parts of Europe. • Dark hair is dominant to light hair in southern Europe but recessive to light hair in northern Europe. • Dark hair is dominant to light hair in northern Europe but recessive to light hair in southern Europe.

9. Imagine a locus with four different alleles for fur color in an animal. The alleles are named Da, Db, Dc, and Dd. If you crossed two heterozygotes, DaDb and DcDd, what genotype proportions would you expect in the offspring? • 25% DaDc, 25% DaDd, 25% DbDc, 25% DbDd • 50% DaDb, 50% DcDd • 25% DaDa, 25% DbDb, 25% DcDc, 25% DdDdDcDd • 50% DaDc, 50% DbDd • 25% DaDb, 25% DcDd, 25% DcDc, 25% DdDd

10. Imagine a family with two parents who both maintain low fat levels through a combination of aerobic activity and weight training. Which of the following statements is/are most likely to apply to their two children? • The parents’ fat levels are irrelevant to the fat levels of the children. • One child is likely to have low fat levels but the other is more likely to have high fat levels because of independent assortment of genes. • The children may not have the same fat levels as their parents because genes independently assort during meiosis.

11. Envision a family in which the grandfather, age 47, has just been diagnosed with Huntington’s disease. His daughter, age 25, now has a 2-year-old baby boy. No one else in the family has the disease. What is the probability that the daughter will contract the disease? • 0% • 25% • 50% • 75% • 100%

12. Review the family described in the previous question. What is the probability that the baby will contract the disease? • 0% • 25% • 50% • 75% • 100%

13. Imagine that you are the daughter in the familydescribed in the previous questions. You had been planning on having a second child. What kind of choices would you make about genetic testing, for yourself and for your child?

14. When a disease is said to have a multifactorial basis, it means that • both genetic and environmental factors contribute to the disease. • it is caused by a gene with a large number of alleles. • it affects a large number of people. • it has many different symptoms. • it tends to skip a generation.