Question

In the Melandrium album, absence of which segment of Y chromosome leads to development of a female plant?
(A) Suppressor region
(B) Promoter region
(C) Fertility region
(D) Pairing region

Answer 1

The majority of flowering plants are bisexual with male and female reproductive organs or parts on the same flower or the different flowers of the same plant. About 5 percent of angiosperms are unisexual or dioecious having male and female parts on the different plants. The study of sex determination in plants was done on Coccinia, Asparagus, and Melandrium.

Complete answer:
Melandrium album also called Silene latifolia is unisexual or dioecious plant belonging to Family Caryophyllaceae. The diploid set of chromosomes in the Melandrium album is 24 (2n).
Melandrium album shows XX-XY type of sex determination but the mechanism is quite different. Female plants will have genotype AAXX and male plants will have genotype AAXY. The Y chromosome plays an important role in sex determination. The Y chromosome has a female suppressing gene and a male determining gene which is important for the development and maturation of fertile anther in male plants.
The Y chromosome has 4 parts called Segment I, II, III, and IV, and the X chromosome has 2 parts i.e Segment IV and V.

Segment I: suppresses femaleness causing inhibition of female flower development
Segment II: causes anther development.
Segment III: helps in the late stage of anther maturation
Segment IV: pair with segment IV of the X chromosome
Segment V: promote femaleness
So, the absence of segment I (suppressor region) of the Y chromosome will lead to the development of the female plant.

So, the correct answer is option (A) Suppressor region.

Note:
Normally, plants with genotype AAXY are males but in some cases genotype AAXY can be hermaphrodite or andro hermaphrodite. This happened due to the mutation or deletion of the female suppressor region on the Y chromosome because lack of segment I will promote femaleness and the presence of segments II and III will promote maleness leading to the formation of bisexual flowers.