Plant height is a polygenic trait in a particular species - VCE - SSCE Biology - Question 26 - 2013 - Paper 1

The genotype M'M' RR' S'S' will contribute:

• From gene locus 1 (M'): 2 cm
• From gene locus 2 (R'): 2 cm
• From gene locus 3 (S'): 2 cm

Thus, the total height from this parent is: $2 + 2 + 2 = 6 ext{ cm}$

The offspring will inherit one allele from each parent for each locus:

• For gene locus 1: Possible heights from parents are 5 cm (MM) and 2 cm (M')
• For gene locus 2: Possible heights from parents are 5 cm (RR) and 2 cm (R')
• For gene locus 3: Possible heights from parents are 5 cm (SS) and 2 cm (S')

Calculating all combinations:

• Maximum potential height: $5 + 5 + 5 = 15 ext{ cm}$ (all dominant alleles)
• Minimum potential height: $2 + 2 + 2 = 6 ext{ cm}$ (all recessive alleles)

Other combinations yielding heights:

• One dominant, two recessive: $5 + 2 + 2 = 9 ext{ cm}$
• Two dominant, one recessive: $5 + 5 + 2 = 12 ext{ cm}$

The most likely height that can form combinations of these genes is: $21 ext{ cm}$

From the calculations, the height that corresponds to the various combinations is 21 cm, which matches option C in the multiple-choice answers.