BY: G. SAI MANVITHA

SEX DETERMINATION: XX-XO

SUBMITTED TO: DR. SHEFALI RAIZADA

INTRODUCTION Sex Determination is a biological process that determines the sex of

an organism whether it is male, female, or some times Hermaphrodite.

The first experimental evidence of sex determination is by the discovery of sex chromosomes in some male insects by Henking in 1891.

Henking named them as X-body after called as X-chromosomes.

Y chromosomes are discovered by Stevens in 1908 in drosophila. After so many experiments also people believed that the sex

determination of organisms is due to sex chromosomes only and autosomes play not role in determination.

It is true in case of Mammals and some plants but in organisms like Drosophila, Birds, many plant species etc. autosomes also are also involved in sex determination.

Sex Determination of organisms (animals and plants) is of different mechanisms.

1> Environmental Sex Determination. Ex: Larvae of sea worm, Labroides, plants like melons, cucumber etc. 2> Chromosomal Sex Determination. • XX-XY type, XX-XO type • ZZ-ZW type, ZZ-ZO type 3> Sex Determination by Genic Balance Theory. Ex: Drosophila.

CHROMOSOMAL SEX DETERMINATION

XX-XO is a type of heterogametic male sex determination. In this type of sex determination females will posses two X-

chromosomes [XX] there by are known as Homogametic Females.

Whereas males posses only one X-chromosome and are Heterogametic Males

Heterogametic males contain XO chromosomes in which O or zero represents the absences of another X-chromosomes.

O will not determine sex of organisms.

XX-XO Type

If the X carrying ovum is fertilized by the X carrying sperm, the resulting zygote XX will develop into a female

If the sperm carrying no chromosome unites with the ovum, the zygote XO will develop into male.

Maternal gametes always contain an X chromosome so the sex of the animals offspring depends on whether a sex chromosome happens to be present in male gamete or not.

Most organisms determined by this system have two sex chromosomes XX and are Hermaphroditic and producing both egg and sperm.

Some Drosophila species have XO males. These are thought to arise via the loss of the Y chromosome.

Some organisms that are determined by this system are Grasshoppers, Crickets, Cockroaches, model organisms like Caenorabditis elegans , some plants like vallisnaria, etc.

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