Question

Choose the correct feature about the following phenomena.
I. Incomplete dominance
II. Co-dominance
III. Multiple alleles

• A. Established by means of independent assortment
• B. Follow Mendelian principles
• C. Both a and b are correct
• D. Exceptions to Mendelian principles

Answer 1

The correct option is D Exceptions to Mendelian principles

Incomplete dominance is when in a heterozygous individual the dominant allele does not completely mask the effects of a recessive allele and the organism's resulting physical appearance shows a blending of both alleles.
Example - The inheritance of flower colour in snapdragon (Antirrhinum sp)

In co-dominance both alleles are simultaneously expressed in the heterozygous individual. Example - AB blood group.

Multiple alleles refer to the occurrence of more than two alleles for a particular gene.
Example - The gene (I) which controls ABO blood groups in humans has three alleles -$(I^A,I^B,i)$.

Since Mendel believed that factors (alleles) occur in pairs and in a dissimilar pair of factors one member of the pair dominates (dominant) the other (recessive), incomplete dominance, Co-dominance and multiple alleles are exceptions to Mendelian principles.

Mendel performed crosses between plants differing in two characters known as dihybrid cross and proposed a set of generalisations which we call the law of independent assortment. The law states that ‘when two pairs of traits are combined in a hybrid, segregation of one pair of characters is independent of the other pair of characters’.