Problem set 3Problems 14.8, 14.9, 14.10, 14.121. The normal sequence of a certain Drosophila chromosome is ABC*DEFGHI,where the * represents the centromere. Aberrant chromosomes with thestructures shown below were isolated. In parts a) and b), give the correct termfor each type of rearrangement and show how each rearranged chromosomewould pair with its normal homolog during meiosis I (label the chromosomes inyour drawings).a) ABC*DHGFEIb) ABC*DEFEFGHIc) Draw the meiotic products resulting from of a single crossover between F andG of the paired homologs of part a).2. The structures of two Drosophila autosomes (N1 and N2) and two reciprocaltranslocation chromosomes are illustrated below.N1DfN2RoughT1T2The circles represent the centromeres. The position of the wild-type Rough geneon chromosome N2 and the position of a small deficiency (Df) of chromosomeN1 are shown. Mutations in Rough (ro -) lead to a recessive adult rough eyephenotype. Individuals that are homozygous for the deficiency die as embryos.Assume that the Rough gene and the Df are very close to the translocationbreakpoints and that there is essentially no recombination between thebreakpoint 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 muinterval on a Drosophila autosome. rb maps between b and p. A friend crossesa wild-type female to a black body purple eyed male (b p/b p) and 109 of the F1sare wild type and the other 98 have black body and purple eyes. The friendsuspects that the mutant chromosome in the female could contain two pointmutations in the b and p genes, could be a deletion that removes the two genesor could be an inversion has breakpoints within the b and p genes. What do youthink? How would you distinguish between these possibilities?4. Test crosses show that a female Drosophila is heterozygous for mutations intwo closely linked autosomal genes, black body, which results in a black coloredbody, and short bristles, which results in shortened bristles along the body. Thegenes are separated by six map units. What cross would you conduct todetermine whether your strain carries a deletion that removes both genes or twoindependent point mutations in the black body and short bristlesgenes. You onlyhave the heterozygous female and a doubly mutant strain carrying independentmutations in the short bristles and black body genes. Describe the results of thecross 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 fewyears and this has resulted in two miscarriages and then recently, an abnormalchild that died shortly after birth. At the birth of the child, the Normans met with agenetic counselor who took tissue samples from the child before it died. Thecounselor prepared metaphase chromosome spreads of the sample and foundcytogenetic differences between the child's chromosome 22 pair. The counselorthen prepared metaphase chromosomes from both parents. The chromosome22 spreads for both parents and the child are shown below.Claris Norman Abe Norman childcentromerea) 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 discussedin class. Assuming that alternate and both types of adjacent segregation patternsoccur with equal frequency, what is the probability that she will give birth to anormal child? What is the likelihood that she will have a
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