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name:_______________________ student ID:_____________________ Genetics L311 exam 1 September 16, 2016 Directions: Please read each question carefully. Answer questions as concisely as possible. Excessively long answers, particularly if they include any inaccuracies, may result in deduction of points. You may use the back of the pages as work sheets, but please write your answer in the space allotted and please show all your work. Clearly define your genetic symbols. We will not make guesses as to what a particular symbol is intended to mean. Also, don’t assume that strains are truebreeding unless this is stated in the question. Finally, show all your work. Good luck. page 2 _______ (20 points possible) page 3 _______ (26 points possible) page 4 _______ (15 points possible) page 5 _______ (21 points possible) page 6 _______ (18 points possible) total _______ (of 100 points possible) 1 name:_______________________ student ID:_____________________ 1. Short answers (2 points each, 20 points total) A. The somatic cells. cells make up most of the body. These are all the cells except for the germ B. Nondisjunction provided proof for many that the genes must be on the chromosomes. C. Haploinsufficient is when having a single wild-type copy of a gene is not enough to prevent a mutant phenotype. D. Chiasmata are the apparent points of crossing over. E. Different versions of a gene are called alleles . F. Pleiotropy is when mutation of a single gene produces multiple phenotypes. G. The region found on both the X and Y chromosomes is called the pseudoautosomal . For the following, please provide a brief definition of the term given: H. hemizygous: Having only one copy of a chromosome or portion of a chromosome. I. polar body: Meiotic products of oogenesis. These are small cells that are used to dispose of extra copies of chromosomes while still leaving a single, haploid cell with plenty of cytoplasm. J. test cross: Cross of unknown genotype X homozygous recessive. 2 name:_______________________ student ID:_____________________ 2A. What is the most likely mode of transmission of the trait segregating in the family shown below (4 points)? autosomal recessive B. Obligate carriers are individuals who must carry the mutation that produces the trait. Please list the obligate carriers in the pedigree at right (4 points). I-1, I-2, III-2, III-3, III-5, III-6 C. What is the probability that IV-3 carries the mutation (i.e. is heterozygous, 3 points)? 1/2 D. Please provide the genotoypes of the following (3 points): I-1 Aa II-5 A– III-7 A– 3. The mythical deep sea angler, N. rajovicae, is found in isolated populations with a few characteristic differences. Some have long fins whereas others have short fins and some have large scales whereas others have small scales. Presented below are the results of several crosses (12 points). Parental 1 2 3 4 Long fins, small scale X short fins, small scale Long fins, large scale X short fins, small scale Long fins, large scale X long fins, large scale Short fins, large scale X short fins, large scale Long fins, large scales 0 103 451 0 Long fins, small scales 181 98 0 0 Please provide the genotypes of the parental mice for each cross. Long fins, small scale X short fins, small scale Llss X llss Long fins, large scale X short fins, small scale LlSs X llss Long fins, large scale X long fins, large scale LlSS X LlSS Short fins, large scale X short fins, large scale llSs X llSs 3 Short fins, large scales 0 101 158 358 Short fins, small scales 178 99 0 121 name:_______________________ student ID:_____________________ 4. A species of deep-sea yellow sponge has somatic cells containing 3 pairs of chromosomes, one long, one medium and one short. The gene conferring yellow color (Y) is on the long chromosome, a gene (B) that controls behavior leading to some individual’s predilection for wearing square pants is on the medium chromosome and a gene (L) causing obsessive laughter is on the short chromosome. A. A single somatic cell from an individual, named Bob, who is heterozygous for the yellow and laughter genes and homozygous dominant for B undergoes mitosis. Please draw the products of this division, including the genes (6 points). L B Y B y B l L B Y y l B. Please diagram one of Bob’s cell in metaphase II. Include the genes and circle one pair of sister chromatids. Assume no cross overs (5 points). L C. Rarely meiosis can go awry. Please show the products of meiosis I and meiosis II (you need not include all the steps of each division, just the products) where nondisjunction of the long chromosome during meiosis I has occurred. Meiosis II was normal. Show all chromosomes. You do not need to include the genes in your answer (5 points). 4 name:_______________________ student ID:_____________________ 5. A newly discovered species of deep-sea squid, E. qinae, is found to have two true breeding strains. Strain A has yellow skin and long tentacles, while Strain B has blue skin and short tentacles. A cross of males from Strain A and females from Strain B results in offspring that all have blue skin and medium tentacles. Crossing the F1 animals results in the following: 252 blue, medium tentacled females XBXB or b Tt 122 blue, medium tentacled males XBY Tt 126 yellow, medium tentacled males XbY Tt 128 blue, long tentacled females XBXB or b TT 60 blue, long tentacled males XBY TT 65 yellow, long tentacled males XbY TT 120 blue, short tentacled females XBXB or b tt 63 blue, short tentacled males XBY tt 66 yellow, short tentacled males XbY tt 1002 A. Fill in the genotypes of the F2 progeny (9 points). B. If you cross blue-skinned, long-tentacled F2 males by F1 females, what fraction of male offspring will have blue skin and medium tentacles (4 points)? XBY TT X XBXb Tt => ½ will have blue skin and ½ of those will have medium tentacles to answer is ¼ 6. During your explorations of the sea, you find an interesting starfish that grows short spines instead of the long spines characteristic of the species. Intrigued you perform a cross of short-spined (i.e. mutant) X long-spined (i.e. phenotypically wild type) starfish and get the F1 results below. You then cross shortspined F1 amongst themselves to produce the F2’s shown below. F1s: ½ long spine ½ short spine ss Ss F2s 2/3 short spine 1/3 long spine Ss ss Please provide the genotypes of each of the F1 and F2 animals (8 points)? 5 name:_______________________ student ID:_____________________ 7. You discover a population of snails living on a remote Pacific island. The griffins display a variety of beautifully colored shells. You decide to study the genetic basis for the variation in color. You discover that all of the variations in color are the result of naturally occurring mutations that alter the normal brown shell color. You perform a complementation test between 7 of the differently colored animals and find the results shown in the table. A. How many genes do mutations 1 through 7 represent (6 points)? 3 B. Mutations 1, 2, 4 and 5 all produce different shell colors. How can you explain this phenomenon (4 points)? Different alleles of the gene produce different colors (like that rabbit fur color example in class) 1 2 3 4 5 6 7 1 – 2 – – 3 + + – 4 – – + – 5 – – + – – 6 + + + + + – 7 + + + + + – – 8A. In a population of midnight blooming cactus, you find a single mutation in the gr gene that affects flower color. The flowers normally appear white, to be more easily seen by night flying moths. A recessive mutation in gr leads to gray rather than white flowers. You cross homozygous gr mutants and find the results shown below. No other genes are mutant in these plants. How do you explain these results (4 points)? This looks like variable expressivity. B. In studying a different gene, ebn, you find a similarly puzzling result. When you cross homozygous ebn mutants (again, wild type is white), you find the results shown below (i.e. the offspring of cactus homozygous mutant for ebn are either dark blue or white.) No other genes are mutant in these animals. How do you explain these results (4 points)? This looks like incomplete penetrance. 6