Pleiotropy and Multiple Effects of Genes — NEET Biology
✅ Asked in NEET 2018Occasionally, a single gene product may produce more than one effect. For example, starch synthesis in pea seeds is controlled by one gene. It has two alleles (B and b). Starch is synthesised effectively by BB homozygotes and therefore, large starch grains are produced. In contrast, bb homozygotes have lesser efficiency in starch synthesis and produce smaller starch grains. After maturation of the seeds, BB seeds are round and the bb seeds are wrinkled. Heterozygotes produce round seeds, and so B seems to be the dominant allele. But, the starch grains produced are of intermediate size in Bb seeds. So if starch grain size is considered as the phenotype, then from this angle, the alleles show incomplete dominance.
Pleiotropy occurs when a single gene controls multiple traits. In pea seeds, the B gene affects both starch grain size and seed shape simultaneously. Students often confuse this with incomplete dominance because the starch grain size shows intermediate expression in heterozygotes (Bb), while seed shape shows complete dominance (round). The trap is thinking the allele is incompletely dominant overall—it's actually completely dominant for shape but shows incomplete dominance for grain size. Remember: one gene, multiple phenotypes = pleiotropy. NTA tests this to distinguish between dominance patterns and gene effects on different traits in the same organism.
Which of the following pairs is wrongly matched? (NEET 2018)
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