Question

In Melandrium, sex determination is of

• A. XX-XO
• B. ZZ-ZW
• C. XX-XY
• D. XY-XO

Answer 1

The correct option is C XX-XY

Melandruim album (2n = 24), a dioecious species with heteromorphic sex chromosomes (XY, males and XX, females). By 1900, when microscope techniques had become quite well developed and chromosome behaviour was understood, it was noticed that there was one pair of chromosomes that differed from others. In females, the members of this pair were similar, but differ in appearance in other sex (males). The two chromosomes, that were alike (in female) were the same as one of the members of the unlike pair in male. The chromosome which was present in pair in female and single in male was identified as X chromosome. In males, the other chromosome was called as Y. So, the two sexes can be characterized as:

Female = XX

Male = XY

X-chromosomes were first identified by Wilson and Stevens in 1905. The so called XY system occurs in wide variety of animals including Drosophila and mammals, as well as at least in some plants (e.g., Lychnis, an angiosperm).

X and Y chromosomes are called as sex chromosomes (allosomes), the remaining ones of a given complement, which are same in both sexes are called as autosomes. The type of system discussed above is called as XX-XY system.

So, the correct answer is 'XX-XY'.