You cross two inbred tomato varieties with large (strain 1) and small (strain 2)

Question

You cross two inbred tomato varieties with large (strain 1) and small (strain 2) fruit size.  In the F2 progeny, you measure the average diameters of fruits on each plant and genotype them at 4 molecular markers A, B, C, and D which are situated in that order on chromosome 2.  You obtain the following average fruit diameters for each genotype at each of the four marker loci:

Based on these data, which of the following conclusions is most valid?

A) Loci B and C are both QTLs affecting fruit size.

B) One or more genes in the region around loci B and C are QTLs affecting fruit size.

C) There are no QTLs affecting fruit size in this portion of chromosome 2.

D) Locus C is a QTL affecting fruit size.

Mean fruit diameter (cm.) Marker locus Variety 1 homozygote Heterozygote Variety 2 homozygote LOD score (>3.0 is significant) A 22 23 21 0.61 B 24 21 20 3.23 C 26 23 18 4.29 D 23 22 20 1.82

Explanation / Answer

Answerr is (B) There are more than two genes int he regaion around loci B and C are QTLs that affecting fruit size.

This is because the mean diameter sizes of these loci has shown high variance than others. In general, the final outcome any cross will show two extreme homozygous triats with one high numbered heterozygousity. But here, B and C loci along with d has shown high variation in the homozygosity that will lead to the size of the fruits.

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