Question

5. (5) You are working with a farmer who has two varieties of true-breeding corn plants. The Durham variety has dominant alleles for short stature (S), yellow leaf colour (Y) and crinkled leaves (C). The UOIT variety has the recessive alleles for all three genes, tall stature (s), green leaf colour v),and smooth leaves (c). The farmer has mapped the genes and tells you that they are linked as shown below: 7 m.u 18 m.u The farmer has produced an F1 hybrid between the two varieties and has backcrossed this to the UOIT variety. Assuming that there is no interference, he wants you to tell him a. The proportion of the backcrossed progeny that will be phenotypically identical to the b. The proportion of the backcrossed progeny that will be phenotypically identical to the C. The proportion of the backcrossed progeny that will have the stature and leaf texture of d. The proportion of the backcrossed offspring that will have the stature and leaf colour of Durham variety for all three traits. UOIT variety for all three traits. Durham variety but the leaf colour of the UOIT variety. Durham varilety but the leaf texture of the UoiT variety.

Answer 1

In the given question, the distance between the two genes is given as follows Sand Y 7 mu . Yand C 18 mu The calculation of map units includes the double cross overs also. Therefore, the total number of DCO can be calculated as 18 0.0126 or 1.2690 _X_- 100100 The parent genotypes are SYC/SYC and syc/syc. The F1 parent is heterozygous at all the loci and hence, its genotype if SYC/syc. Since it is back crossed to UOIT which is recessive for all the characters, the genotype from the Fl parent, to the progeny, is only given in the table shown below: Genotpye SYC Parental recombinant Parental Parental SCO between S and Y | 2.7% SCO between S and Y | 2.9% SCO betn Y and C SCO betn Y and C DCO DCO Proportion of progeny 37.5% 37.5% SVC SYc svC 8.4% 8.4% 0.6% 0.6% sYc

It is given that map distance between the two genes is 18 and 7 mu, which indicates the percent recombination. Therefore, the total percent recombinants are 25% and parental are 75%. Since there are two parental genotypes, each genotype has 75/2 = 37.5% of the progeny.

While calculating the proportion of SCO, the number of DCO shall be taken into consideration. The total number of DCO is 1.26, and each DCO proportion is 0.6%.

Therefore, the total number of SCO between S and Y genes – 0.7 – 1.2 = 5.8. The proportion of each SCO between S and Y genes is 2.8, that is the genotype sYC = 2.9% and the genotype Syc = 2.9%. The same way, SCO proportion for the genes Y and C is also calculated.

1. The proportion of the backcrossed progeny that will be phenotypically identical to the Durham variety for all three traits is 37.5% or 0.375
2. The proportion of the backcrossed progeny that will be phenotypically identical to the UOIT variety for all three traits is 37.5% or 0.375
3. The proportion of the backcrossed progeny that will have the stature and leaf texture of Durham variety but the leaf colour of the UOIT variety is represent a DCO (genotype SyC). Hence, the proportion is 0.6%
4. The proportion of the backcrossed offspring that will have the stature and leaf colour of Durham variety but the leaf texture of the UOIT variety represent genotype (SYc) and is a SCO between Y and C genes. The proportion in 8.4% or 0.084