In this
post, you will study different types of allele dominance in genetics, including
complete dominance, incomplete dominance, co-dominance, and over-dominance.
Learn about inheritance patterns, Mendelian genetics, and the diverse ways
alleles influence phenotypic expressions.
Categories of Allele Dominance
a. Complete
Dominance
b. Incomplete
Dominance
c. Co-Dominance
d. Over-Dominance
Complete Dominance:
One
allele fully suppresses another, observed in heterozygous state, concealing
recessive allele function. Illustrated in Mendel's round (R) and wrinkled (r)
alleles and various other characters. Instances of novel phenotypes challenge
this principle.
Incomplete Dominance
In
1899, Carl Correns studied four O'clock plants, revealing intermediate
phenotypes in heterozygotes. Cross between red and white flowered plants yields
pink flowers in F1, with F2 ratio of 1:2:1 (red:pink:white). Heterozygous
alleles lead to traits neither dominantly expressed, termed incomplete
dominance.
 |
| Incomplete Dominance |
Co-Dominance
Both
alleles fully manifest in heterozygotes. E.g., human blood groups AB and MN. MN
blood types based on RBC antigens (M and N). Phenotypes M, N, and MN each arise
from alleles LM, LN. When M-blood individual marries N-blood individual,
offspring display MN blood type.
Over Dominance
Heterozygote
phenotype surpasses both homozygotes. Drosophila exhibit this phenomenon, where
heterozygote (w+w) displays more eye fluorescein pigments than wild (w+w+) or
white-eyed (ww) homozygotes.
