Problem Set 2 Key

Problem Set 2 Key - BICD100 FA2011 Problem Set#2...

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BICD100 FA2011 Problem Set #2: KEY ( corrections in red font ) 1). Drawings A-G above ( not shown in key ) represent stages of mitosis or meiosis, or products of meiosis, for an organism whose diploid chromosomal makeup is shown at the upper left (“Diploid cell”). This organism has two pairs of homologous chromosomes – a large pair and a small pair. Chromosomes of maternal origin are shown in red and those of paternal origin are shown in green. Indicate which of the drawings illustrate each of the following (note that some drawings might fit more than one description below or vice versa, or there may be no drawing for some items): Synapsis: A Metaphase of meiosis II: D , F Metaphase of mitosis: B Metaphase of meiosis I: A Haploid product of normal meiosis: C Monosomic product of non-disjunction: G Triploid product of non-disjunction: no drawing (non-disjunction does not produce triploids) Trisomic product of non-disjunction: E Aneuploid product of non-disjunction at meiosis I: E and G (aneuploid can be either monoploid or triploid, and can be produced by non-disjunction at meiosis I or II) Aneuploid product of non-disjunction at meiosis II: ditto above 2). Mendelian ratios are modified in crosses involving autotetraploids. Assume that one plant expresses the dominant trait green seeds and has the genotype WWWW. This plant is crossed to another with the recessive trait white seeds whose genotype is wwww. If only one dominant allele is sufficient to produce green seeds, what proportion of F2 progeny seeds (obtained by selfing F1 plants) do you predict will be white? Assume that synapsis between any two chromosomes carrying a W or w allele is equally likely. 1/36. See discussion of autotetraploids and clicker question asked at the beginning of lecture 5 on Oct. 3 rd … 1/6 of gametes are ww, 1/6 are WW, and 4/6 are Ww. If you construct a Punnett square with these 6 gamete classes across the top and down the side, you get a Punnett Square with 36 cells in it. Only one resulting F2 genotype is wwww so
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