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Incomplete Dominance or Co-Dominance


Not all traits are inherited as the pea seed color, where the yellow color gene dominates over the green color gene. Very often, the combination of different allele genes produces a intermediate phenotype.

This situation illustrates the call incomplete or partial dominance. An example of this type of inheritance is the color of wonder flowers. They can be red, white or pink. Plants that produce pink flowers are heterozygous, while the other two phenotypes are due to the homozygous condition. Assuming that the gene V determine the color red and the gene B, white color we would have:

VV = red flower

BB = white flower

VB = pink flower

Although we have previously used capital letters to indicate dominant and recessive genes respectively, when it comes to incomplete dominance, many authors prefer to use only different capital letters.

Crossing a wonder plant that produces red flowers with another that produces white flowers and analyzing the phenotypic results of the generation F1and F2we would have:

Now analyzing the genotypic results of the generation F1and F2we would have:

P: White flower

B B

V

Red flower

V

BV

pink

BV

pink

VB

pink

VB

pink

F1 = 100% VB (pink flowers)

Crossing now two heterozygous plants (pink flowers), we would have:

F1

Pink flower

V B

V

Pink flower

B

VV

Red

BV

pink

VB

pink

BB

White

F2 = Genotypes: 1/4 VV, 1/2 VB, 1/4 BB.

Phenotype: 1/4 red flowering plants

1/2 pink flowering plants

1/4 white flowering plants