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202 BIOL HOMEWORK #2 Student's Name____KEY______________________ Section number and TA's name:_________________ DUE: Feb 7/8 in your discussion section. IMPORTANT: Please type (not hand-write) your answers onto the question sheet itself (this sheet). Please highlight or otherwise indicate the parts that you have typed with underlining or bolding. If additional working is required, it will be specifically stated so in the question, and whether the working should be shown on the answer sheet or a supplemental sheet will also be stated. 1. The diagram to the right shows the nucleus of a diploid cell prior to replication of the chromosomes (2N=4). Chromosome pairs are named 1 or 2, and either P or M dependent upon whether they arose form the cell's paternal or maternal parent. Centromeres are indicated by a black circle. Draw the products of meiosis assuming both (i) a single crossover involving chromosome two, and (ii) that both paternal centromeres segregate together during the first meiotic division. (2 points) See attached page 1 Point for crossover, 1 Point for both parental centromeres segregate together 2. The diploid chromosome number in humans is 46 (23 pairs), and one member of each chromosome pair is present in each gamete. a. If we ignore for now the possibility of crossing over, how many different combinations of maternal and paternal chromosomes can be found in human gametes? N=23, you can come up with million of different combinations such as #1M, #2P, #3P, #4P, #5P, #6P, #7P, #8P, #9P, and so on to the last chromosome, #23P. The formula is: Possible combinations = 2n, here it would be 223 = 8,388,608 (Assuming no crossing-over) (0.5 for answer, 0.5 for explanation) b. Assuming no crossovers occur, what is the probability that a gamete will contain chromosomes solely from the individual's father? P = 1/ 223 (1 ponit) (2 points) 3. The horse has a diploid set of 64 chromosomes, and a donkey has a diploid set of 62 chromosomes. Mules (viable but usually sterile progeny) are produced when a male donkey is mated to a female horse. How many chromosomes will a mule cell contain? Donkey: 2n= 62 ------n= 31 Horse: 2n= 64 --------n = 32 M Donkey X F Horse = Mule (n= 31) (n = 32) (n = 63 chromosomes) The sterility is attributed to the differing number of chromosomes of the two species. Since there is an odd chromosome one number, of the chromosomes does not have a homologue and which impedes a normal meiosis thus making the mules infertile. (0.5 for right answer, 0.5 for explanation) careful, answer is in online!!!!! (1 point) 4. Prepare a table which compares mitosis and meiosis on the following points. -number of cell divisions that take place -number of progeny cells -ploidy level (haploid or diploid) of parent and progeny cells -types of cells involved (somatic versus sex cells) -similarity in genetic makeup to parent cells # of Cell divisions # of progeny cells Ploidy level types of cells involved Mitosis 1 2 2n parent, 2n daughter Somatic Identical (if no mutation) Meiosis 2 4 2n parent, n daughter Sex cells Different similarity to parent cells (0.1 per "cell") (1 point) 5. In a species of the cat family, eye color can be gray, blue, green or brown. In separate crosses involving homozygous parents, the following data were obtained. The character (eye colour) is inherited by the same mechanism in each cross. Cross P1 parents F1 offspring All green All green All green F2 offspring 9/16 green; 3/16 brown; 3/16 gray; 3/4 green; 1/4 brown 3/4 green; 1/4 gray ______ A Gray x brown 1/16 blue B C Green x brown Green x gray a. How many genes are involved in the inheritance of eye color? 2 genes (0.5 points) b. Devise genetics symbols for these gene(s) and alleles, and indicate the genotypes of the P1 parents for each of the three crosses above. Cross ______ A Gray x brown aaBB x AAbb All green AaBb 9/16 green; A_B_ 3/16 brown; A_bb 3/16 gray; aaB_ 1/16 blue; aabb 3/4 green; 1/4 brown AABB, AABb, AAbB AAbb 3/4 green; 1/4 gray AABB, AaBB, aABB, aaBB P1 parents F1 offspring F2 offspring B C Green x brown AABB X AAbb All green AABb Green x gray All green AABB X aaBB AaBB 1 point for right answer, 0.5 for explanation (2 points) 6. In mice, black fur color is conferred by the dominant allele B, and brown fur is conferred by the recessive allele b. The Color gene, C, controls whether pigment can be made, with the recessive c allele resulting in albinism. a. If I have an albino mouse, what are its possible genotypes for the "B" and "C" genes? BBcc, Bbcc, bbcc (1 point) b. If I wanted to determine the genotype of this mouse, to what genotype should I cross this animal: bbCC (1 point) (2 points) ... View Full Document

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