Question

Starch synthesis in the pea seed is controlled by one gene. It has two alleles $B$ and $b$. If starch grain size is considered as the phenotype, then from this angle allele show

• A. Multiple allele
• B. Incomplete Dominance
• C. Co-dominance
• D. Polygenic inheritance

Answer 1

Answer: (B)

• Occasionally, 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.