In incomplete dominance, the genes of an allelomorphic pair are not expressed as dominant or recessive.

1. Incomplete dominance
Deparment Of Botany
Preapared by
Dr. P. B.Cholke
(Assistant Professor in Botany)
Pune District Education Association’s
Anantrao Pawar College ,Pirangut,
Tal-Mulshi, Dist-Pune- 412115

2. Incomplete dominance
• i. In incomplete dominance the genes of an
allelomorphic pair are not expressed as dominant or
recessive.
• ii. They express them self partially when present
together in hybrid.
• iii. One gene cannot suppress the expression of the
other completely.
• iv. As a result F1, hybrid shows characters
intermediate to the effect of two genes of the parent.
• v. In such cases both the alleles of contrasting
characters express as blend or mixing.

3. • Examples :
• Incomplete dominance is found in both
plants and animals.
• Good examples are Mirabilies jalapa.
(Four ‘o’ clock plant) and Anterrihinum majus
(snapdragon)

4. • e.g Four ‘O’clock plant (Mirabilis jalapa)
• i) When pure breeding red flowered plants (RR)
are crossed with pure breeding white flowered
plants (rr) then the F1 progeny shows pink flower
(Rr)
• ii) Both alleles express themselves to produce an
intermediate colour i.e. pink such alleles are said
to be incomplete dominance.
• iii) When pink flowered F1 plants are inbreeded
the F2 - phenotype ratio is 1 : 2 : 1
• In Incomplete dominance both genotypic and
phenotypic ratio are identical or equal or similar
i.e. 1:2:1

6. Co-dominance
• i. Co-dominance is a phenomenon of two
contrasting alleles of same gene lacking dominant
recessive relationship.
• ii. Both the alleles when present together in
heterozygous individuals, express their two traits
independently.
• iii. The dominant allele is not able to suppress or
incompletely dominate the recessive character.
• iv. Both the genes of allelomorphic pair express
themselves equally in F1 hybrid.

7. • e.g. Roan coat colour in cattle.
• For example, when a cattle with black coat is
crossed to a bull with white coat.
• F1 hybrids possess roan coat. In roan coat,
both black and white patches appear separately.
So, the alleles which are able to express
themselves independently when present
together are called co-dominant alleles.
• In Co-dominance both genotypic and phenotypic
ratio are identical or equal or similar i.e. 1:2:1