Articles

Complementary gene action


The color of the smell peas flower

Bateson and Punnet described another case of gene interaction by analyzing flower color inheritance in pea plants.

The flowers on these plants may be white or purple in color. Crossing two white flowering plants of different origins, obtained in F1 only plants producing purple flowers. These interchangeable F1 individuals produced in F2 two types of phenotypes, in the proportion of: 9/16 plants producing pupura flowers and 7/16 plants producing white flowers.

In this case, we also have the interaction of two gene pairs in determining a character (flower color). The purple color is conditioned by the interaction of the two dominant genes, A and B (A_B_).

For the occurrence of white flowers, we have two possibilities:

  • The presence of only one of the dominant genes, A or B (A_bb or aab_); or
  • The absence of the two dominant genes (aabb).
GenotypesPhenotypes
A_B_ purple
A_bb white
aaB_ white
aabb white

Detailing the crossings made with white flowers of different origins, we have:

PAAbb X aaBB
F1

AaBb

purple flowers

AaBb X AaBb

Possible gametes: AB, Ab, aB, ab

Let's see the intersection in detail:

ABAbabab
AB

AABB

Purple

AABb

Purple

AaBB

Purple

AaBb

Purple

Ab

AABb

Purple

AAbb

White

AaBb

Purple

Aabb

White

ab

AaBB

Purple

AaBb

Purple

aaBB

White

aaBb

White

ab

AaBb

Purple

Aabb

White

aaBb

White

aabb

White

F2

Summary table

Phenotypic proportions obtained from the crossing between double heterozygotes in different forms of interaction of two genes, with independent segregation. Note the correlation between genotypic and phenotypic proportions for each case.

Interaction TypesGenotypes
A_B_ A_bb aaB_ aabb
Classic aspect ratio 9 3 3 1
Dominant epistasis 12 3 1
Recessive epistasis 9 3 4
Double genes with cumulative effects 9 6 1
Dominant Double Genes 15 1
Recessive Double Genes 9 7
Dominant and recessive interaction 13 3