Question

How are traits inherited?

1. Dominant/recessive (Mendelian)

2. Incomplete Dominance

3. Codominance

4. Multiple Alleles (ABO blood group)

5. Multiple Genes (including Epistasis)

Answer 1

Traits can be inherited and expressed in various way namely,

Codominance is a situation in which both the alleles present in an organism are expressed. In a heterozygote, both the alleles are dominant instead of one allele. In humans, the best example is blood groups. In blood grouping three alleles are present. They are A, B and O. The A and B alleles are both dominant to the O allele. Person with genotype AA or AO has the blood type A. Person with genotype BB or BO has the blood type B. Person with genotype OO has neither A or B alleles. Person with genotype AB has both A and B alleles. In this case, both A and B alleles are codominant.

Incomplete dominance is a pattern of inheritance in which one of the alleles show partial dominance, in other words, neither allele of a particular trait is dominant over the other. This results in the expression of a trait that is the combination of both dominant and recessive phenotypes.

Epistasis is a phenomenon in which one gene masks or otherwise affect the phenotype of another. It is the interaction between the different genes but not between the alleles of the same gene.

Some traits possess allele which are dominant over the recessive allele. Hence if the dominant allele is present only that trait is expressed. A dihybrid cross (consist of two traits) of two heterozygous individuals (each individual has one of each allele) results in a phenotypic ratio or 9:3:3:1. This phenotype is obtained only when an allele is dominant over the other.