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
5.
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