State two ways in which meiosis gives rise to genetic variation. Using different colors to distinguish chromosomes of maternal and paternal origin, draw a metacentric set of homologous chromosomes at: b. Prophase I during synapsis but before recombination.
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Copyright 2022 Richard Cripps Page 1 NAME_____________________________ INSTRUCTIONS: 1. Write your answers on the paper, and hand in the assignment at the end of the test. 2. If you need extra space for calculations, write them on the back of the sheet. 3. Read the questions CAREFULLY; jargon can often be confusing if you do not read the question thoroughly. 4. Pace yourself; donÕt spend all your time on a difficult question when you could be making up easier points elsewhere. Make sure you leave time to complete the test. Question 1. a. State two ways in which meiosis gives rise to genetic variation. Using different colors to distinguish chromosomes of maternal and paternal origin, draw a metacentric set of homologous chromosomes at: b. Prophase I during synapsis but before recombination. c. Prophase I after a single crossover between two of the non-sister chromatids. d. Anaphase I (make sure you include the results of the crossover described above). e. Anaphase II (draw all cells and make sure you include the crossover results). (20 points) Question 2. Distinguish briefly between haploid cells and diploid cells. Give an example of each. (8 points) Question 3. a. What is non-disjunction ?
Copyright 2022 Richard Cripps Page 2 b. The attached sheet shows the karyotype of four human individuals (A through D). Complete the following table to identify the sex, and the chromosomal aberration or name of the syndrome. Individual Sex Aberration or syndrome name A B C D c. For individual C, propose two mechanisms by which this karyotype could have occurred. d. For individual D, indicate which parent contributed the extra chromosome. (18 points) Question 4. In watermelons, bitter fruit (B) is dominant to sweet fruit (b), and yellow spots (S) is dominant to no spots (s). The genes for these two characters assort independently. A pure-breeding plant that has bitter fruit and yellow spots is crossed to a pure-breeding plant that has sweet fruit and no spots. a. What will be the genotype and phenotype of the F1 ? b. If the F1 plants are selfed, what will be the phenotypic ratios in the F2 (be sure to include the numbers and the phenotypes)? c. If instead the F1 plants are testcrossed, what will be the genotypic and phenotypic ratios in the offspring? (12 points) Question 5. In trying to breed the perfect tomato plant (a diploid flowering plant), I have been carrying out some simple genetic experiments. I recently crossed a true-breeding tall plant to a true-breeding short plant. All of the F1 offspring were of intermediate height. Assuming that plant height is controlled by a single gene, use genetic symbols to explain the F1 phenotype, and indicate the relationship between the two alleles (e.g., dominant, or recessive, or Éetc.). What phenotypes would I observe in the F2 if the F1 plants were self-fertilized, and at what ratios ? (9 points)
Copyright 2022 Richard Cripps Page 3 Question 6. In corn, a color in the aleurone (part of the seed) arises from the dominant allele A. The recessive allele, a, produces an aleurones with no color. Leaf color is controlled by a second, linked gene, L. The recessive allele, l, causes plants to become yellow, whereas the dominant L allele confers a green leaf color. When I test-crossed a plant with unknown genotype to a true-breeding plant that had colorless aleurones and yellow leaves I obtained the following progeny: Coloured, yellow 12 Coloured, green 88 Colourless, yellow 92 Colourless, green 8 a. Indicate which offspring are Recombinats and which are Parentals. b. Calculate the recombination frequency between the A and L genes. Show your working. c. Draw the genotype of the unknown parent and indicate if it was trans- or cis. (12 points) Question 7. Using one sentence for each example, explain five lines of evidence in support of the chromosome theory of heredity. i. ii. iii. iv. v. (10 points)(34)
Copyright 2022 Richard Cripps Page 4 Question 8. A pedigree for failure of blood clotting, or hemophilia, and red-green color blindness is shown below. Individuals with hemophilia show blue shading, and those with color blindness show black shading. a. Are hemophilia and the color blindness traits X-linked or autosomal? Explain briefly. b. Are the traits recessive or dominant? Explain briefly. c. Indicate which individuals in generation III are recombinants for the two genes. d. Using the first nine offspring in generation III only (1-9), determine the recombination frequency between these two genes. (16 points)(50)
Copyright 2022 Richard Cripps Page 5
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