BIO 325 - Fall 2009 - Sample questions - Exam 2-1

BIO 325 - Fall 2009 - Sample questions - Exam 2-1 -...

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GENETICS (BIO 325) Fall 2009 Sample questions – Exam 2 __________________________________________________________________________________________________ 1. Listed below are four modifed dihybrid ratios, where each ratio represents a type of gene interaction. For each of these interactions, what phenotypic ratio is expected in the progeny of a testcross when the dihybrid is used as a parent? Mention the ratios and genotypes for each class. (You may use the symbols A and B to denote the dominant alleles and a and b to denote the recessive alleles.) (a) 9: 3: 4 (b) 9: 7 (c) 12: 3: 1 (d) 13: 3 (e) 15: 1 2. The following pedigree is for an autosomal dominant trait. What does this pedigree tell you about the genotype of individual A and this trait? 3. (a) A true-breeding red snapdragon was crossed to a true-breeding white snapdragon. The F 1 progeny were red. In the F 2 generation, the following progeny were observed: 1820 red 590 pink 790 white 3200 Which type of gene interaction explains these results? (b) In a certain breed of dog, the alleles B and b determine black and brown coats respectively. However, the allele Q of a gene on a separate chromosome is epistatic to the B and b color alleles resulting in a gray coat (q has no effect on color). If animals of genotype B/b ; Q/q are intercrossed, what phenotypic ratio is expected in the progeny? 4. Fill the ovals shown below to indicate your understanding of (a) a trait that shows incomplete penetrance, (b) a trait that is 100% penetrant but exhibits variable expressivity, and A
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(a) (b) (c) 5. Four Hfr strains of E. coli are known to transfer genes during conjugation in the following order. Hfr strain Order of gene transfer 1 arg – thy – mal – met – thi - thr 2 mal – met – thi – thr – azi – bio – try 3 phe – his – try – bio – azi – thr – thi 4 his – phe – arg – thy – mal All the Hfr strains are derived from the same F + strain. Construct a genetic map showing the order of genes in the original F + chromosome. Also indicate on this map the site of insertion of F and the direction of transfer of the chromosome for each Hfr strain. 6. A particular Hfr strain (that is pro + ) normally transmits the pro + marker as the last one in conjugation. In a cross of this Hfr strain with a F - strain (pro - ), some pro + recombinants are recovered early in the mating process. When these pro + cells are mixed with F - cells, the majority of the F - cells are converted into pro + cells that also carry the F factor. Explain these results. 7. In a transformation experiment, donor DNA was obtained from a prototroph bacterial strain (a + b + c + ), and the recipient was a triple auxotroph (a - b - c - ). The following transformant classes were recovered. a
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BIO 325 - Fall 2009 - Sample questions - Exam 2-1 -...

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