Question

By giving suitable examples based on the hints, explain there are various situations which differ from Gregor Mendel’s hypothesis.
Hints:
(a) Incomplete dominance
(b) Co-dominance
(c) Polygenic inheritance

Hint:

Remember: Mendel’s laws apply to simple traits, but real-life inheritance often involves incomplete dominance, co-dominance, and multiple genes.

Answer 1

Step 1: Understand Mendel’s hypothesis.
Gregor Mendel proposed that traits are controlled by pairs of factors (genes) where one allele is dominant over the other, leading to clear dominant and recessive phenotypes. However, some inheritance patterns do not follow this simple dominance rule.
Step 2: Incomplete dominance.
In incomplete dominance, neither allele is completely dominant over the other, resulting in an intermediate phenotype.
Example: When red flowered (RR) and white flowered (rr) plants are crossed, the F$_1$ generation shows pink flowers (Rr), which is a blend of both traits.
Step 3: Co-dominance.
In co-dominance, both alleles express themselves equally in the heterozygous condition.
Example: In human blood group system, individuals with genotype AB have both A and B antigens expressed simultaneously.
Step 4: Polygenic inheritance.
In polygenic inheritance, a single trait is controlled by multiple genes, leading to continuous variation rather than distinct categories.
Example: Human skin colour is determined by multiple genes, resulting in a wide range of shades rather than just two types.
Step 5: Conclusion.
These patterns show that inheritance can be more complex than Mendel’s laws, as traits may show blending, equal expression, or continuous variation instead of simple dominant-recessive relationships.