21. With a certain Hfr strain, the transfer of genes during conjugation proceeds

Question

21. With a certain Hfr strain, the transfer of genes during conjugation proceeds in the following order ser ---- met ----- leu ----- arg ----> The Hfr strain with the genotype arg+ leu+ met+ ser+ is conjugated with an F- strain arg- leu- met- ser-. The exconjugants are selected for inheritance of the ser+ allele. When these ser+ colonies were tested for inheritance of the remaining alleles, the following results were found: 45% of all cells were arg- 30% of all cells were leu- 10% of all cells were met- Disregard quadruple crossovers. Map distances between the loci (in the direction from ser to arg) are:
The Answer is 10 m.u. – 20 m.u. – 15 m.u... My question is in regards to how we go about acquiring these numbers. Please show your work..

Explanation / Answer

According to the give data, the percent of cells with respect to the ser+ are

ser+ arg- = 45%

ser+ leu = 30%

ser+ met = 10%

So, the recombinant frequencies are in this proportions. Mapp distances can be calculated by these proportions. This gives the following result

ser........10%(10 m.u.).....met

ser........30%(30 m.u.).....leu

ser........45%(45 m.u.).....arg

ser.............met...........leu............arg

ser<---10......><.....20.....><......15.....>

<................30............>

<.......................45.....................>

So, this is the arrangement of the genes with respective map distances.

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