Page 6 - Lesson Notes- Principle of inheritance & Variation

Dominance Recessive

When a factor (allele) expresses

itself in the presence or absence of It can only express itself in the absence of or its
(i)
its dominant factor called recessive factor allele.

dominance.

It forms a incomplete defective enzyme which
It forms a complete functional
(ii) fails to express itself when present with its
enzyme that perfectly express it.
dominant allele, i.e., in heterozygous condition.

2. Law of Segregation- alleles do not blends and both the characters are recovered during
gametes formation as in F2 generation. During gametes formation traits segregate (separate)

from each other and passes to different gametes. Homozygous produce similar kinds of gametes

but heterozygous produce to different kinds of gametes with different traits.

Incomplete dominance

It is a post Mendelian discovery. Incomplete dominance is the phenomenon of neither of
the two alleles being dominant so that expression in the hybrid is a fine mixture or

intermediate between the expressions of two alleles.

In snapdragon (Mirabilis jalapa), there are two types of pure breeding plants, red
flowered and white flowered. On crossing the two, F1 plants possess pink flowers. On

selfing them, F2 generation has 1red: 2 pink: 1white. The pink flower is due to

incomplete dominance.

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