Problem set 3 Problems 14 8 14 9 14 10 14 12 1 The normal sequence of a certain Drosophila chromosome is ABC DEFGHI where the represents the centromere Aberrant chromosomes with the structures shown below were isolated In parts a and b give the correct term for each type of rearrangement and show how each rearranged chromosome would pair with its normal homolog during meiosis I label the chromosomes in your drawings a ABC DHGFEI b ABC DEFEFGHI c Draw the meiotic products resulting from of a single crossover between F and G of the paired homologs of part a 2 The structures of two Drosophila autosomes N1 and N2 and two reciprocal translocation chromosomes are illustrated below Df Rough N1 N2 T1 T2 The circles represent the centromeres The position of the wild type Rough gene on chromosome N2 and the position of a small deficiency Df of chromosome N1 are shown Mutations in Rough ro lead to a recessive adult rough eye phenotype Individuals that are homozygous for the deficiency die as embryos Assume that the Rough gene and the Df are very close to the translocation breakpoints and that there is essentially no recombination between the breakpoint and Rough and between the breakpoint and the Df a You cross T1 N1 Df T2 N2 ro females x T1 N1 Df T2 N2 ro males What is the frequency of dead embryos produced in this cross b What is the frequency of adults with rough eyes produced in the above cross 3 Black body b reduced bristles rb and purple eyes p all map within a 5 mu interval on a Drosophila autosome rb maps between b and p A friend crosses a wild type female to a black body purple eyed male b p b p and 109 of the F1s are wild type and the other 98 have black body and purple eyes The friend suspects that the mutant chromosome in the female could contain two point mutations in the b and p genes could be a deletion that removes the two genes or could be an inversion has breakpoints within the b and p genes What do you think How would you distinguish between these possibilities 4 Test crosses show that a female Drosophila is heterozygous for mutations in two closely linked autosomal genes black body which results in a black colored body and short bristles which results in shortened bristles along the body The genes are separated by six map units What cross would you conduct to determine whether your strain carries a deletion that removes both genes or two independent point mutations in the black body and short bristlesgenes You only have the heterozygous female and a doubly mutant strain carrying independent mutations in the short bristles and black body genes Describe the results of the cross if the mutation is a deletion and if it is a double mutant 5 Abe and Claris Norman have been trying to have children for the last few years and this has resulted in two miscarriages and then recently an abnormal child that died shortly after birth At the birth of the child the Normans met with a genetic counselor who took tissue samples from the child before it died The counselor prepared metaphase chromosome spreads of the sample and found cytogenetic differences between the child s chromosome 22 pair The counselor then prepared metaphase chromosomes from both parents The chromosome 22 spreads for both parents and the child are shown below centromere Claris Norman Abe Norman child a Do the parents have an abnormal chromosome 22 and if so which parent s and what is the nature of the abnormality be specific b How did the child s abnormal chromosome arise c Why is the child abnormal d Do you think this couple is capable of having additional abnormal children Why e Do you think this couple is capable of having normal children Why 6 An adult woman has the 14 21 Robertsonian translocation that we discussed in class Assuming that alternate and both types of adjacent segregation patterns occur with equal frequency what is the probability that she will give birth to a normal child What is the likelihood that she will have a miscarriage
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