Question

Regarding the sex determination in the Melandrium album, consider the following statements.
1. The Y chromosome is longer than the X chromosome
2. The Y chromosome and X chromosome form a heteromorphic bivalent at meiosis
3.It is the presence of a single Y chromosome rather than any number of X chromosomes or autosomes that give a male individual.
Which of the statements given is correct?
A. 1 and 2 only
B. 2 and 3 only
C. 1 and 3 only
D. 1, 2, and 3

Answer 1

Hint: Mechanism of sex determination id different in animals. Chromosomes are of two types. They are autosomes and allosomes. Allosomes are also called sex chromosomes. It is the type of sex chromosomes that determines the sex is various animals.

Complete answer:
Melandrium alba is a type of plant in which several sex-determining experiments were done. The diploid chromosome number of this species is 24. Melandrium alba shows a sex chromosomal type of sex determination. It is the number of the X chromosome that determines the sex and it is often designated to be the sex chromosome. In humans, sex determination is of XY type. Here, both males and females have the same number of chromosomes. Males have X chromosome and Y chromosome whereas the female has two X chromosomes.
In Melandrium alba, XY type of sex determination is followed, but the method is different from the typical XY type as in humans. In Melandrium, males are designated as AAXY and females as AAXX. Here, the Y chromosome is only seen in males and not in females. Y chromosomes are longer than X chromosomes and they are both from a heteromorphic bivalent during meiosis. Males can be designated as XY, XXY, XXXY, etc.
Hence, the correct option is A.

Note: Male heterogamety is a condition in which male produces two types of gametes. In female heterogamety, females produce two different types of gametes in terms of sex chromosomes. Male heterogamety is seen in humans and female heterogamety can be seen in birds.