Question
the question of interest is the number 3 only
Chromosoma!Variation d T Prahlenes You hybridize 2 ed spel y diffe der of gl bel ote: cent location of the centromere). Species B Species A cent a d c A B C D E a) A single crossover takes place between genes B and Con non-sister chromatids in the F1 hybrid Draw a diagram showing the configuration you would expect to see during prophase I and anaphase l of the first meiotic division. Indicate the positions of the centromeres and the 5 genes in each case. b) How would your answer to part (a) effect the fertility of the hybrid c cent d I------ 12-------I----8-----1---6- l map units A homozygous stock of wild type flies was crossed with a stock homozygous for recessive mutants a, b, c, d and e. Fi females (wild type phenotype) were back to the mutant parental stock The only phenotypes of the back cross progeny were phenotyp requency 0.4 b c d 0.44 0.0 0.02 0.0 0.04 a) Calculate the pairwise recombination frequencies as observed by this cross. Why are these pected b) Describe two possible changes in chromosome structure that could cause such discrepancies in recombination frequencies. Why is oneofthe possibilities is unlikely in this example? c) For the more likely case, draw the pair of chromosome homologues of the Fl female at prophase I. Show the gam products of a crossover occurring between the d and e loci. Which of the gametes produced may be inviable and why 3) Three closely related diploid species A, B and Ceach possessing two chromosomes per gamete are rossed to pl hybrids. al reg a, b, c, d, u, d x, Each ch al reg e species. map units in length Gamate from Species A: Gamate from Species B: Gamate from Species C A-B hybrid. Wi A-B hybrid Diag the eff Briefly exp b) Diag meiosis in the A-Chybrid. Will the A-Chybrid have the same fertility as its parents? What are the effects on fertility, if any, of a crossover in the w-x region? Briefly explain your c) Diag meiosis in the B-Chybrid. Will the B-Chybrid have the same fertility as its parents the eff lity y, of Briefly exp 4) Regions of DNA that contain transposable elements are more prone to duplications, deletions, and inversions, Describe two mechanisms that could account for this observation
Explanation / Answer
3.
a). Fertility is so difficult for hybrids. During meiosis, genetic material is exchanged between the two pairs of chromosomes (chromosome of species A with chromosome of species B)
A and B have very similar genes located at particular position on the chromosome. Hence they can have similar fertility as their parents. If there is crossover between w-x region, since they are situation at the end of the chromosome not much difference in fertility will occur between hybrid and parents.
b) same as of A-B hybrid. These will also have similar fertility as their parents.
c) the B-C hybrid shows a lot variation in fertility with their parents because species B and species C have genes not similar with each other in position/ location of genes on the chromosome. These two have distant similar genes. If crossover occurs between w-x, gene order differs because the genes change their location and cannot be determined which genes can pair, present in different chromosomes and hence it will not have same fertility as its parents.
