Describe the differences among dominance, incomplete dominance, codominance, and overdominance. Solution Dominant character: A character that expresses itself even in the heterozygous state in F1 generation is known as a dominant character. With such a character, the F2 ratio is a 1:2:1 and F1 is a 3:1 ratio in case of mono hybrid cross. Incomplete dominance: It is also known as incomplete or partial or a semi dominant condition , where none of the alleles are dominant or recessive over the other. This condition is characterised where the F1 heterozygous do not show a single colour/ trait relative to one parent, but express a phenotype that is intermediate to both the parents. For eg: if a red flower plant of Mirabilis jalapa is crossed with the white ones, then the F1 will not be red or white but pink in colour. In case where the pink F1 is crossed to obtain F2 a ratio of 1:2:1 is obtained with red:pink:white in both genotypic and phenotypic ratios. Codominance : the co dominant alleles do not have a a dominant or recessive effect from one another. Here, the heterozygous genotype gives rise to a phenotype that is very much different from either of the parents. This can very well be seen in the ABO blood grouping system . The chemical glycoproteins are controlled by three alleles out o which two IA and IB are co dominant where as i is recessive to the other two at the ABO locus. The IAIA and IAi individuals produce type A blood, and IBIB and IBi individuals produce type B blood, but IAIB individuals show modifications on their blood cells and thus show type AB blood, so the IA and IB alleles are said to be co-dominant. Overdominance : this is the condition where the heterozygote phenotype does not lie in the range of any of the homozygotes. For eg the sickle cell anaemic condition in humans. The individual with this effect will have a partial resistance to malaria but the homozygotes do not show any such kind of effects..

1. Describe the differences among dominance, incomplete dominance, codominance, and
overdominance.
Solution
Dominant character: A character that expresses itself even in the heterozygous state in F1
generation is known as a dominant character. With such a character, the F2 ratio is a 1:2:1 and
F1 is a 3:1 ratio in case of mono hybrid cross.
Incomplete dominance: It is also known as incomplete or partial or a semi dominant condition ,
where none of the alleles are dominant or recessive over the other. This condition is
characterised where the F1 heterozygous do not show a single colour/ trait relative to one parent,
but express a phenotype that is intermediate to both the parents. For eg: if a red flower plant of
Mirabilis jalapa is crossed with the white ones, then the F1 will not be red or white but pink in
colour. In case where the pink F1 is crossed to obtain F2 a ratio of 1:2:1 is obtained with
red:pink:white in both genotypic and phenotypic ratios.
Codominance : the co dominant alleles do not have a a dominant or recessive effect from one
another. Here, the heterozygous genotype gives rise to a phenotype that is very much different
from either of the parents. This can very well be seen in the ABO blood grouping system . The
chemical glycoproteins are controlled by three alleles out o which two IA and IB are co
dominant where as i is recessive to the other two at the ABO locus. The IAIA and IAi
individuals produce type A blood, and IBIB and IBi individuals produce type B blood, but IAIB
individuals show modifications on their blood cells and thus show type AB blood, so the IA and
IB alleles are said to be co-dominant.
Overdominance : this is the condition where the heterozygote phenotype does not lie in the range
of any of the homozygotes. For eg the sickle cell anaemic condition in humans. The individual
with this effect will have a partial resistance to malaria but the homozygotes do not show any
such kind of effects.