11. A blue plant with large petals is testcrossed. The following progeny are rec
ID: 149969 • Letter: 1
Question
11. A blue plant with large petals is testcrossed. The following progeny are recovered no. recovered blue, large petals blue, small petals white, large petals white, small petals 155 48 52 145 a) Are the genes for color and petal size: linked, unlinked, or cannot tel? Briefty explain why? b) Is the pattern due to independent assortment, crossing over, or cannot tell? Briefly explain why? c) If B-blue, b-white, P-large petals, p-small petals, if possible indicate the genotype of the two parental strains in the cross. d) If possible to determine, what is the map unit distance between B and P?Explanation / Answer
a) The genes for color and petal size are linked because the frequency of the recombinant phenotypes is less than that of parental phenotype i.e. blue plant with large petals. Heterozygous test cross of unlinked genes gives 1 : 1 : 1 : 1 phenotypic ratio which is not observed here. Thus, the genes are linked.
b) The pattern observed during gene linkage is due to the absence of crossing over or independent assortment. The frequency of parental strains is highest. Thus, blue plant with large petals, and white plant with small petals are the parental strains.
c) Blue, large petals - BbPp
White small petals - bbpp
d) Distance between any two genes can be estimated by calculating recombination frequency. Two genes are said to be located 1 map units apart if they show recombination frequency of 1%.
Here, Recombination frequency =(No. of recombinant offspring / Total offsprings)x 100
Map unit distance between B and P = (48 + 52 / 155 + 48 + 52 + 145) x 100
= (100/400) x 100
= 25 map units.
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