What is the inheritance pattern observed in the size of starch grains and seed shape of Pisum sativum? Workout the monohybrid cross showing the above traits. How does this pattern of inheritance deviate from that of Mendelian law of dominance?

Solution

The starch synthesis in pea plants is controlled by a single gene. It has two alleles B and b. BB homozygotes produce starch effectively and therefore produce large starch grains. Whereas the bb homozygotes are less efficient in starch production and hence produce smaller grains. After maturation the BB seeds were found to be round and bb was wrinkled. Heterozygotes produce round seeds, and so B was considered to be the dominant allele. But when they were crossed the resultant progeny were intermediate-sized Bb seeds.

P generation BB × bb

↓

F₁Generation Bb × Bb

(long grains)

(intermediate grains)

(small grains)

Deviation from Mendel's law of dominance: If starch grain size is considered as the phenotype, then one can see that the alleles show incomplete dominance. Thus, dominance is not an autonomous feature of a gene, it depends on gene product and production of particular phenotype from the product.

Some More Questions From Principles of Inheritance and Variation Chapter

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Principles Of Inheritance And Variation

What is the inheritance pattern observed in the size of starch grains and seed shape of Pisum sativum? Workout the monohybrid cross showing the above traits. How does this pattern of inheritance deviate from that of Mendelian law of dominance?

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