Unformatted text preview: 244 Chapter 14 14-6. W a. Each of the strains shows pseudodominance for some of the mutant alleles; that is, each ‘1 ‘ strain is mutant for one or more of the marker genes. Furthermore, after the diploids undergo
‘1‘; ; meiosis, two of the spores die. All of these are indications that the X-rays induced deletion mutations. 1 II b. Two spores in each ascus die because they receive the deleted homolog. The deletions remove ! some essential genes from the chromosomes and this is lethal in a haploid. g' c. There is only one X-ray induced mutation per strain, so all genes that show pseudodominance
are on the same chromosome. Using this logic, all four genes: w, x, y, and z, are on the same
chromosome. (1. The order is w y z x =x z y w. Genes w and y are deleted in strain 1, uncovering the w" and y' W alleles, so w and y are adjacent. Genes x, y, and z are deleted in strain 2 so they must be adjacent. f ‘ Combined from the information from strain 1, this means the order must be w y [x z], with the brackets indicating that you don’t know the relative order of x and 2. Strain 3 is deleted for w, y, and 2, therefore the gene that follows y must be 2. Note that two answers are given because you . i cannot determine the left-to-right orientation of this group of four genes.
\ 14-7. Remember that sister chromatids are identical to each other. The probe will anneal to homologous DNA on the chromosome and produce a signal at that position. Genotype: Den/0612 Genotype: Del1/Del2 Genotype: 09/1/4- robe B Probe C 1 Probe A
' ‘55 ,_
5 ‘ Del 1 Deli? 5/7 09/2
No hybridization _
't Genotype: Inv1l+ Genotype: [/7112 /+
‘ l‘w" Probe B + Inv2 + Note that in the paracentric Inversion 2, regions homologous to Probes A and B are not inverted and 9:15 thus stay at the original position near the telomere, while regions homologous to Probe C in the bottom right ﬁgure are inverted and thus move closer to the centromere. y! deletions remove portlons of polytene chromosome region 65 (which turns out to be on chromosome
I 3, a Drosophila autosome). Deletion A shows pseudodominance for javelin and henna, so all or part ...
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- Spring '08