Hfr strains

In E.coli, four streptomycin-sensitive, prototrophic Hfr strains were mated with a stretomycin-resistant F^- strain auxotrophic for a number of nutritonal requirements. Matings were interrupted at various intervals, and cells were plated on streptomycin-containing minimal meduim supplemented with particular nutrients to test for gene transfer. Entry time (in minutes) of the first five genes for the four strains were as follows: Hfr strain 1 : M+ (4), Z+(6), X+(11), W+(15),C+(17.5) Hfr strain 2 : L+ (1), A+ (2), N+(5), C+ (6.5), W+(9) Hfr strain 3 : A+(2.5), L+(3.5), B+(6), R+(11.5), U+ (15) Hfr strain4 : Z+ (3), M+(5), U+ (11), R+(14.5), B+(20) draw the map of the E.coli genome consi... click for more

Map Distances

Time of entry mapping between a streptomycin-sensitive, prototrophic Hfr strain and a streptomycin- resistant Fminus strain that was Trp- Pyr- Cys- Nic- did not allow the order of the trp,pyr,cys genes to be determined, but these three genes were always transferred before nic. To determine the relative order of the trp,pyr,cys genes and the distances between them, the Hfr and Fminus strains were mated long enough to allow the transfer of the nic gene, after which Trp+ recombinants were selected. The unselected pyr and cys genes were then scored in the Trp+ recombinants , yielding the following results: phenotype number of recombinants Trp+ Pyr+ Cys+ 7... click for more

E.coli

A nutritionally defective E.coli strain grows only on meduim containing thymine, whereas another nutritionally defective strain grows only on meduim containing leucine. When these two strains are grown together , a few progeny are able to grow on minimal meduim with neither leucine nor thymine. How can this result be explained?

A recessive mutation in the human genome...

1. A recessive mutation in the human genome results in a condition called anhidrotic ectodermal dysplasia, which is associated with an absence of sweat glands. The condition can be detected by studies of the electrical conductivity of the skin, because skin without sweat glands has a lower electrical conductivity (higher resistance) than normal skin. In kinships in which the recessive allele is segregating, affected males are found to show low conductance uniformly across their skin surface, as do affected females. However, many females show a mosaic pattern with normal conductance in some patches of skin and low conductance in others. The pattern of tissue lacking sweat glands is differ... click for more

Grandchildless

1. You have isolated a recessive Drosophila mutant that you call grandchildless (gls) because it behaves in the following way: Cross: gls/gls female x +/+ male F1: All sterile If you perform the reciprocal cross, however, you find that the result is different from that in cross 1: Cross: gls/gls male x +/+ female F1: All fertile F2 (from crossing F1 males and females): All fertile F3 (from crossing F2 males and females): ¼ sterile, ¾ fertile a. Explain the grandchildless mutant. If the fertile F3 are mated, what will the ratio of fertile:sterile be in the F4? b. You isolate a new allele of the gls gene (gls*) which behaves in the following way: Cross: gls... click for more