Q43 - Polygenic Inheritance of Plant Height
Refer to the question paper for figures and tables.
Q43. If 45 cm is the basal height and a gardener selfs plants with genotype M0M1 N0N2 O0O3 P0P4, what proportion of plants would be 65 cm tall?
1/256: To reach 65 cm from a 45 cm base requires an additional 20 cm. The selfing parent contributes alleles summing to 0+1+0+2+0+3+0+4 = 10 cm per gamete pair. For exactly 20 cm additional height, the offspring needs allele combinations summing to 20. Each gene independently assorts with probability 1/4 for each homozygous class and 1/2 for heterozygous. The only way to get exactly 20 cm is the genotype M1M1 N2N2 O3O3 P4P4, each with probability 1/4. So (1/4)^4 = 1/256.