Genetics, Fall 2005 TEST 2, 11/16/05 Page 1

Transcription

1 Genetics, Fall 2005 TEST 2, 11/16/05 Page 1 STUDENT NAME: Give a brief definition of the following terms (5 points each; only nine definitions count for the grade): 1. phenotype 2. homozygous 3. codominance 4. epistasis 5. Barr body 6. testcross 7. X-linked 8. centimorgan

2 Genetics, Fall 2005 TEST 2, 11/16/05 Page 2 9. allele 10. pleiotropy Give brief answers to the following problems (5 points each; only eleven answers count for the grade): 1. Siamese cats exhibit a light fur color with dark areas on the legs, the tail, the nose, and the ears. Explain the basis for this coloration. 2. Is it possible for a couple to have children with all four ABO blood types? If so, what would the genotypes of the parents have to be? 3. A carrier of the sickle cell allele (Hbβ S ) usually does not show disease symptoms. Therefore, sickle cell anemia is considered a recessive genetic disease. However, what is the dominance/recessiveness relationship between the sickle cell allele and the normal allele (Hbβ A ) in a carrier with respect to the β-globin polypeptide? the concentration of red blood cells at high altitudes? the susceptibility to malaria?

3 Genetics, Fall 2005 TEST 2, 11/16/05 Page 3 4. A man whose red blood cells do not react with anti-a or anti-b antibodies and a woman with blood type A have a child with blood type AB. Give a possible explanation for this finding (other than the man is not actually the father of the child); include all possible genotypes for the father. 5. Hemophilia A is a disease in humans that is characterized by a defect in blood clotting. It is inherited as a recessive, X-linked trait. For the purpose of this question we can call the disease allele A and the normal allele N. What are the probabilities that a son is affected by the disease, if the mother is affected (genotype X A /X A )? is a carrier (genotype X A /X N )? or if the father is affected (genotype X A /Y)? (In all cases the other partner has only normal hemophilia alleles!) 6. In a particular breeding experiment, the F 1 generation of true-breeding parents was found to be phenotypically uniform. Mating individuals of the F 1 generation with each other yielded an F 2 with 3 different phenotypes. Name two modes of inheritance that may explain these findings. Include the expected phenotypic ratios for the F 2 generation! 7. In Labrador retrievers fur color is controlled by two genes. One gene controls pigment production with the dominant B allele producing a black pigmentation and the recessive b allele a brown pigmentation. The other gene controls the deposition of the pigment in the hair with the dominant E allele producing a functional transport system and the recessive e allele a nonfunctional transport system. The genotype of a true-breeding black lab is B/B, E/E. Name all possible genotypes of a true-breeding chocolate lab and a true-breeding yellow lab.

4 Genetics, Fall 2005 TEST 2, 11/16/05 Page 4 8. The brown eyes gene (symbol: bw) and the black body gene (symbol: b) are located on Drosophila chromosome 2. True-breeding flies with brown eyes were crossed with true-breeding flies with black bodies. Testcrossing the uniform wildtype F 1 generation yielded the following offspring: 90 flies with brown eyes, 100 wildtype flies, 120 flies with black bodies, and 90 flies with brown eyes and black bodies. Do the above numbers reveal that bw and b are linked genes? To answer this question perform a χ 2 -test under the assumption that the two genes assort independently. 9. Below you see different combinations of sex chromosomes in individuals; the number of autosomes is normal in each case. What is the sex of the individuals, if they were humans, or if they were flies? How many Barr bodies would you see in the cells of these individuals? Sex Chromosomes Human Drosophila Sex Barr bodies Sex Barr Bodies X0 XX XY XXY 10. Below you see the electrophoretic analysis of blood samples for the presence of a particular protein. The father of the analyzed family is homozygous for the fast running form of the protein (1), the mother is homozygous for the slow running form (2). Lane 3 shows the result for a mixture of blood from the father and the mother, and lane 4 shows the blood of their heterozygous daughter.

5 Genetics, Fall 2005 TEST 2, 11/16/05 Page 5 Is the functional form of the protein a monomer or a dimer? In lane 5, add the expected protein pattern in a blood sample of the heterozygous daughter, if the gene were located on the X-chromosome. 11. One form of red-green color blindness in humans is caused by a recessive, X-linked allele (let s call this allele b, and the normal allele of the gene B). Explain why more males are affected by this form of color blindness than females. 12. According to the one-gene-one-enzyme hypothesis a gene is a part of the genome that controls the production of an enzyme. Name two aspects of gene function that are not covered by the one-gene-oneenzyme concept.