Question

In an Hfr X F-cross, leu+ enters as the first marker, but the order of the other markers is unknown. If the Hfr is wild-type and the F-is auxotrophic for each marker in question, what is the order of the markers in a cross where leu+ recombinants are selected if 27 percent are ilet, 13 percent are mal+, 82 percent are thr+, and 1 percent are trp+?

Answer 1

Leu+ is the first marker, other recombinants are

27% Ile+

13% mal+

82% thr+

1% trp+

The order of genes depends on their distance from the ori site. The genes present near the ori site enter first during conjugation and having the highest number of recombinants. In 82% recombinants, thr+ is present, which means it enters first. The second highest of the recombinats are ile+( 27%) and the third highest is the mal+ (13%). The trp+ is present in the lowest number of recombinants only 1%.

So complete order of the marker is

Leu+, thr+ Ile+ Mal+ Trp+