Question

Problem 2 The following numbers were obtained for testeross progeny in Drosophila (phenotypes): + m + 218 W + 236 + + 168 wm+ 178 + m 95 W + + 101 wm Total 1000 Construct a genetic map by calculating map distances and determining gene order.

Answer 1

The most frequent pair of phenotype class tell us the genotype of original parental combination . here offspring of '+ m +' and 'w + f' combination are most frequent ( 218, 236 respectively) hence +m+ and w+f are the original parental combination .

the second and 3rd most frequent genotypic combination are the result of single crossing over here offspring of '+ + f ', 'w m +', '+ m f' , ' w + +' ( 168,178,95,101 respectively) genotypic combination are the result of single cross over (S C O).

and the least genotypic frequency are the result of double cross over . here offspring of ' + + + ' ,' w m f ' ( 3,1 respectively ) genotypic combination are the result of double cross over ( D C O ).

Tennantri To calculate frequency of map distance D.C.O and we have to determine frequency of S.C.O. a frequency of D.C.O Total number of offspring of D.C.O combination = 3+1 = 4 as + ++ = 3 : wmf = 1 The frequency of D...O - Total offspring X 100 - XIDO (218+236 + 168 + 178 +95 +101 + 3 + 1 4X100 1000 = 0.4 % To determine the order of gene first we have to determine middle gene. To determine middle gene we have to compain parental comler nation and D.C.O Combination .. Parental Combination are - tmt wtf. and D.C.O Combination are - +++, want .. + m + oss) I double cross over occurs betwen. wtf w and m' and m and f 7 if the D.C.O of parental combination resulta - wmf + + + Inesembles with given DCO then the order of parents the connbination is right the order. This combination is nessembler with the given. D.c.o combination hence 'm' is the middle gene and the order of gene w m f

S.c.o frequency between w and in will be m + + 13 t (parental) [w. - gene order wmt, & tf combination Total number of this offspring of this genotype = 178 (wmt) + 168 (+ ++) 346 w between and m the best Therefore S.C.O frequency - X 100 178 Total offspring 178 x100 I w 1000 gene order. 346 This is s.c.o 1 frequency I between Wand m S.C.O frequency between m and f [ This s.c.o frequency will be s.c.o-2 in between m and fi + m + (Parental) and the frequency wtf of s.c.o between m and of - tmf, wtt combination . 196 Total of number = this comtination 196 - 95 (+ mf) + 107 (w++) bination -X100 total offspring Χ Ιστο 1000 196 = 196 = 19.6 %

The distance is = s.c.o-1 between frequency w and D.C.0 m frequency & = 34.6 = 35 The distance Summation of + 0.4 map whit map unit. between in and f is equal to S.c.o-2 frequency and D. co frequency + frequency D.C.0 frequency S.C.O-2 - 19.6 + 0.4 map unit. = 20 mu.. There fore, the genetic map will be actual w 35 mum 20 mu and the genetic w mf order is

[ to calcalute middle gene first we have to take parental comnbination in given order ( in this question given order of parental combination are + m +   and w + f then we compair DCO combination of parental to the given DCO combination . if both combination resembles the the order of parental genotype is the actual gene order if resultant DCO does not resemble with given DCO then we should interchange gene position i.e interchange of w and m and f untill the resultant DCO resembles with given DCO .]