Assume that the length of wheat leaves is controlled by three loci, each with tw

Question

Assume that the length of wheat leaves is controlled by three loci, each with two alleles: L andI, Wand w Hand h. Determine the differences in leaf length between two homozygous strains of wheat. Assume each allele contributes equally to the length of the plant leaves. One homozygous strain, Il ww hh, has leaves that are 100 mm in length, and the other strain, LL wW HH, has 220 mm leaves. The two homozygous strains are crossed, and the resulting F1 are selfed to produce F2 progeny. What length will the leaves of the ll ww HH genotype plant be? Number min What proportion of the F2 progeny will have the same phenotype as the ll ww HH genotype? Number

Explanation / Answer

Since llwwhh gives 100 mm in length
and LLWWHH gives 220 mm in length
Hence, each dominant allele ends up contributing (220-100)/6 = 20 mm in length.

Length of the leaves of the llwwHH genotype plant would be
= 2 dominant alleles
= 100 mm + 2 * 20 mm
= 140 mm in length

The proportion of the F2 progeny that will have the same phenotype as the llwwHH genotype
= Proportion of the F2 progeny that display 2 exactly 2 dominant alleles
= 6C2
= 15 possibilities out of 64 progeny
= 15/64 proportion of 2 dominant allele individuals, hence length of 100 + 2 * 20 = 140 mm length

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