Question

S. Imagine that you set up a three-point mapping crus to determine the orier or three (linked genes. You have recessive mutations available for all three genes: Follow (1) 1hite (r) and echinus (ec). A heterozygous F, Drosophila female is crossed to a hemizygous mutant male. The observed numbers and phenotypes of Fz are as follows: 4685 yellow, white, echinus 4759 wild type 80 yellow 70 white, echinus 193 yellow, white 207 echinus 3 yellow, echinus 3 white Based on this data answer the questions in the following order (each answer yields a clue useful in following question): (a) Determine which of the above phenotypic classes represent the parental types and the recombinant types (specify SCO, DCO). (b) Identify the reciprocal classes of phenotypes. (c) Determine which gene is in the middle. (d) Calculate the recombination frequency (% RF) based on the observed F2 numbers of es pair of reciprocal classes. (e) Calculate the gene distances. (f) draw a genetic map of the 3 genes (include the gene location, symbol and mu, between earch CO

Answer 1

A Parental Types Wild YNE + + t / Double Gloss over (sco) yellow, while echinus = 4685 Yellow Echinus 3 , while 3 = 4759 VE ht - + + + + + w By Comparing parental genotype & double cross over, we can day that w is moving, so it is the middle gene, Order is w e + + Single Cross Over 6/W Y & W (sco) yellow (80) white echinus (70) single cross over 67w w f t (sco) yellow, while (193) echinus (207) gene ( so Gene distance a gene distance between Y & W & # of recombinants 6/0 scot # of oco - Total # of progeny 80 + 70 + 3 + 3 0.0156 x 100 = 1.56 mu 10,000 6) gene distance 610 wee 193 + 207 + 3 + 3 x 100 4.06 mU 10,000 d) recombinant frequency of pair of reciprocal dans - 6 xloo 0.06 10,000 y 4.06 mu 1. 56