XX-XY sex determination is one of the chromosomal sex determination where sperm determines the sex of the progeny. This type of sex determination is seen in plants also. MELANDRIUM ALBUM is one.

1. By:
Akshatha.S.Ravi

2.  Melandrium album is a model dioecious plant
species with an X/Y chromosome based sex
determination system.
 Genotypical Male plants – AAXY
Female plants – AAXX

3.  Sometimes AAXY can be a hermaphrodite (all flowers
are bisexual) or androhermaphrodite (forming both
bisexual and male flowers on the same individual).
 Gametogenesis of X-Y happens in male meiosis
 The occurrence of bisexual flowers can be caused
by mutation(deletion) of female suppressing gene
on Y chromosome or as a consequence of a
spontaneously, artificially induced change in DNA
methylation patterns.

4.  In Melandrium album , Y chromosome plays an
important role in sex determination as it contains
female suppressing gene and male determining
gene responsible for mature anther development.
 Y chromosome is longer than X chromosome and
they form a heteromorphic bivalent at meiosis.

5.  X and Y chromosome have common segment IV,
which helps in pairing and regular disjunction of X
and Y chromosomes during meiosis.
 The remainder of Y chromosome has 3 segments
namely,
Segment I – Supresses femaleness
Segment II - initiates anther development
Segment III- controls late stage of anther
development

6.  X chromosome has a differential segment V, which
promotes femaleness in the absence of female
suppressing segment I on Y chromosome.
2A+XX 1.00 female
2A+XY 0.5 male
2A+XXY 1.00 female
3A+XXY 0.67 male (occasional)
4A+XXY 0.5 male
4A+XY 0.25 male (occasional)
4A+XXXY 0.75 male (occasional)
4A+XXXXY 1.00 hermaphrodite