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The following is the biochemical pathway for purple pigment production in flowers of sweet pea:

Colorless precursor 1 —- Allele A—->  Colorless precursor 2 —--- Allele B—---> Purple pigment

Recessive mutation of either gene A or B leads to the formation of white flowers. A cross is made between two parents with the genotype: AaBb × aabb. Considering that the two genes are not linked, the phenotypes of the expected progenies are:


Option: 1

9 purple : 7 white

Option: 2

3 white : 1 purple

Option: 3

1 purple : 1 white

Option: 4

9 purple : 6 light purple : 1 white

Answers (2)


From the Punnett square, we can see that the resulting genotypes are as follows:

AABB: Purple pigment (phenotypically purple flowers)

AABb: Purple pigment (phenotypically purple flowers)

AaBB: Purple pigment (phenotypically purple flowers)

AaBb: Purple pigment (phenotypically purple flowers)

AAbb: No purple pigment (phenotypically white flowers)

Aabb: No purple pigment (phenotypically white flowers)

aaBB: No purple pigment (phenotypically white flowers)

aaBb: No purple pigment (phenotypically white flowers)

Therefore, the expected phenotypes of the progeny from the cross AaBb × aabb would be a combination of purple and white flowers, with a ratio of 4:4, or 1:1, for purple to white flowers. Hence, the correct answer is option 3.


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Gautam harsolia

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In case of 'duplicate recessive epistasis homozygous recessive gene masks the other gene i.e., aa is epistatic to A or a || bb is epistatic to B or b

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