Principles of Inheritance and Variation — Part 2: Beyond Mendel; chromosomes and linkage: visual lesson, CBSE Class 12 Biology

Lesson

Beyond Mendel

Part 2 — patterns that do not follow the simple 3 : 1, and how genes on chromosomes explain them.

In this lesson you will

Explain incomplete dominance, co-dominance and multiple alleles with examples
Explain pleiotropy and polygenic inheritance
State the chromosomal theory of inheritance
Explain linkage and recombination from Morgan’s experiments

Concept

Incomplete dominance

In the snapdragon (Antirrhinum), true-breeding red (RR) × white (rr) gives a pink F1 (Rr): neither allele is completely dominant, so the heterozygote is intermediate.

Diagram

Snapdragon F2

With incomplete dominance the phenotypic ratio equals the genotypic ratio: 1 : 2 : 1, because each genotype has its own phenotype.

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