Independent Assortment 2 PDF

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Supplemental questions for chapter 3: independent assortment....

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1. When two genes fail to assort independently, the term normally applied is _________. A. B. C. D. E.

discontinuous inheritance Mendelian inheritance linkage tetrad analysis dominance and/or recessiveness

Answer: C 2. Assume that a cross is made between AaBb and aabb plants and all the offspring are either AaBb or aabb. These results are consistent with the following circumstance: A. B. C. D. E.

complete linkage. alternation of generations. codominance. incomplete dominance. hemizygosity.

Answer: A 3. Assume that a cross is made between AaBb and aabb plants and the offspring fall into approximately equal numbers of the following groups: AaBb, Aabb, aaBb, aabb. These results are consistent with the following circumstance: A. B. C. D. E.

independent assortment. alternation of generations. complete linkage. incomplete dominance. hemizygosity.

Answer: A 4. Assume that a cross is made between AaBb and aabb plants and the offspring occur in the following numbers: 106 AaBb, 48 Aabb, 52 aaBb, 94 aabb. These results are consistent with the following circumstance: A. B. C. D. E.

sex-linked inheritance with 30 % crossing over. linkage with 50% crossing over. linkage with approximately 33 map units between the two gene loci. independent assortment. 100% recombination.

Answer: C

5. The phenomenon in which one crossover increases the likelihood of crossovers in nearby regions is called A. B. C. D. E.

chiasma. negative interference. reciprocal genetic exchange. positive interference. mitotic recombination.

Answer: B 6. The genes for mahogany eyes and ebony body are approximately 25 map units apart on chromosome III in Drosophila. Assume that a mahogany-eyed female was mated to an ebony-bodied male and the resulting F1 phenotypically wild type females were mated to mahogany, ebony males. Of 1000 offspring, what would be the expected phenotypes and in what numbers would they be expected? Answer: mahogany = 375; ebony = 375; wild type = 125; mahogany-ebony = 125. 7. Assume that there are 12 map units between two loci in the mouse and that you are able to microscopically observe meiotic chromosomes in this organism. If you examined 200 primary oocytes, in how many would you expect to see a chiasma between the two loci mentioned above? Answer: 48 8. Phenotypically wild F1 female Drosophila, whose mothers had light eyes (lt) and fathers had straw (stw) bristles produced the following offspring when crossed to homozygous light-straw males: PHENOTYPE light-straw wild light straw

NUMBER 22 18 990 970 Total 2,000

Compute the map distance between the light and straw loci. Answer: 2 map units

9. Assume that the genes for tan body and bare wings are 15 map units apart on chromosome II in Drosophila. Assume also that a tan-bodied, bare-winged female was mated to a wild type male and the resulting F1 phenotypically wild type females were mated to tan-bodied, bare- winged males. Of 1000 offspring, what would be the expected phenotypes and in what numbers would they be expected? Answer: wild type = 425; tan-bare = 425; tan = 75; bare = 75 10. Assume that investigators crossed a strain of flies carrying the dominant eye mutation Lobe on the second chromosome with a strain homozygous for the second chromosome recessive mutations smooth abdomen and straw body. The F1 Lobe females were then backcrossed with homozygous smooth abdomen, straw body males and the following phenotypes were observed: smooth abdomen, straw body Lobe smooth abdomen, Lobe straw body smooth abdomen Lobe, straw body

820 780 42 58 148 152

(a) Give the gene order and map units between these three loci. (b) What is the coefficient of coincidence? Answers: (a) Lobe is in the middle. smooth abdomen---5---Lobe-----------15-------------straw body (b) zero 11. In Drosophila, assume that the gene for scute bristles (s) is located at map position 0.0 and that the gene for ruby eyes (r) is at position 15.0. Both genes are located on the X chromosome and are recessive to their wild type alleles. A cross is made between scute-bristled females and ruby-eyed males. Phenotypically wild F1 females were then mated to homozygous double mutant males and 1000 offspring were produced. Give the phenotypes and frequencies expected. Answer: scute = 425; ruby = 425; wild type = 75; scute-ruby = 75 12. Assume that a cross is made between AaBb and aabb plants and that the offspring occur in the following numbers: 106 AaBb, 48 Aabb, 52 aaBb, 94 aabb. These results are consistent with what arrangement of genes? Answer: In the AaBb parent, the dominant alleles are on one homolog and the recessive alleles are on the other.

13. In the fruit fly, Drosophila melanogaster, a spineless (no wing bristles) female fly is mated to a male that is claret (dark eyes) and hairless (no thoracic bristles). Phenotypically wild type F1 female progeny were mated to fully homozygous (mutant) males and the following progeny (1000 total) were observed. PHENOTYPES

NUMBER OBSERVED

spineless wild claret, spineless claret claret, hairless hairless, claret, spineless hairless hairless, spineless

321 38 130 18 309 32 140 12

(a) Which gene is in the middle? (b) With respect to the three genes mentioned in the problem, what are the genotypes of the homozygous parents used in making the phenotypically wild F1 heterozygote? (c) What are the map distances between the three genes? A correct formula with the values “plugged in” for each distance will be sufficient. (d) What is the coefficient of coincidence? A correct formula with the values “plugged in” will be sufficient. Answers: (a) hairless (b) cl h +/cl h + and + + sp/+ + sp (c) cl-------30-----h---10---sp (d) .03/.03 = 1

14. Assume that two genes are 80 map units apart on chromosome II of Drosophila and a cross is made between a doubly heterozygous female and a homozygous recessive male. What percent recombination would be expected in the offspring of this type of cross? Answer: 50 (maximum)

15. Sister chromatid exchanges increase in frequency in the presence of Xrays, certain viruses, ultraviolet light, and certain chemical mutagens. In what autosomal recessive disorder is there known to be an increase in sister chromatid exchanges? Answer: Bloom syndrome 16. At what stage of the meiotic cell cycle and during what chromosomal configuration does crossing over occur? Answer: prophase I 17. Chiasma: A. Are actual exchanges between homologous chromosomes. B. Are the cytological mechanism for crossing over. C. Occur at the 4-strand (tetrad) level in homologous pairs of chromosomes. D. All of the above. E. None of the above. Answer: D 18. The number of linkage groups in each species should equal the __________________ Answer: haploid number of chromosomes 19. Suppose a cross of AaBb X aabb yields the following numbers of offspring: AaBb 140, Aabb 12, aaBb 14, aabb 138. A. This suggests that A and B are linked on the same chromosome. B. This suggests that the A and B loci are not linked on the same chromosome. C. It cannot be determined whether the A and B loci are linked to the same chromosome. D. The crossing over percentage between A and B is about 25%. E. None of the above. Answer: A...