Question

In Melandrium, the sex determination type is
A) XX-XY type
B) XX-XO type
C) ZZ-ZW type
D) XY-XO type
E) XO-ZZ type

Answer 1

Hint:Melandrium album (2n=24) is a dioecious species that has heteromorphic sex chromosomes and incorporates a strong genetic commitment for sex determination.

Complete answer:
Sex determination mechanism in Melandrium album was proposed by HE Warmke. In Melandrium, Y chromosome is longer than X-chromosome, and that they form a heteromorphic bivalent at meiosis. The X and Y chromosomes were divided into five different segments. These segments are known to regulate different stages of development of sex organs. The X and also the Y chromosomes have a standard segment IV, which helps in pairing and regular disjunction of X and Y chromosomes during meiosis. The rest of sex chromosome has three segments, namely I, suppressing femaleness; II, initiating anther development and III, controlling late stage of anther development. The X-chromosome also includes a differential segment V, which should promote femaleness within the absence of female suppressing segment I on Y chromosome.

Segment I: Suppress femaleness: it inhibit the event of female structure within the flower
Segment II: Initiate anther development
Segment III: Control later stages of anther development
Segment IV: Homologous with the region IV on X chromosome
Segment V: Chromosome specific region

A plant with AAXY constitution that lacking segment I of sex chromosome thanks to mutation or deletion, are bisexual. This is often because, within the absence of segment I on the sex chromosome (whose function is to suppress femaleness) the segment V on X chromosome promote the event of female structures.

Therefore, the correct answer is option A, XX-XY type.

Note: In Melandrium album four whorls of floral organs are observed in both male and feminine floral meristems, because it is that the case for any hermaphrodite species. They're sepals, petals, stamens and carpels. At the first stages of flower development, the floral meristem is totally undifferentiated and similar in male and feminine plants. When the floral development proceeds, there'll be considerable difference within the relative proportion of various floral parts in both male and feminine plants. In male flowers (AAXY), a sterile filament is developed in situ of the carpels. Similarly in female flowers (AAXX) the developments of anthers are first initiated but rapidly it degenerates, whereas five carpels are developed within the centre.