2. What is sex determination?
The method by which distinction between male and
female is established in an organism under genetic
control.
The sex chromosomes are responsible for
determination of separate sexes.
It is a biological system that determines the
development of sexual characteristics in an organisms.
Traditionally, the symbol ♂ designates male
and the symbol ♀ designates female.
3. The XX-XY type of chromosomal
sex determinations
Since the female are XX , as a result of meiosis during the
formation of gametes the egg cell contain only one type of
egg.
The males consist of XY, and produce two type of sperm.
Out of which half of the sperm consist of X chromosome
and the other half consist of Y chromosome.
During fertilization, if the sperm containing X
chromosomes fuses with the egg, the zygote XX develops
into female.
While the sperm containing Y chromosomes fuses with an
egg to produce a male with XY chromosomes.
4.
5. Homogametic: The female is called the homogametic
sex because only one type of gamete(X-bearing) is
produced.
Heterogametic: The male is called as heterogametic
sex because two different gametes(X and Y – bearing)
are produced.
6. Sex ratio: The ratio of sex at fertilization is expected to
be 1:1 because males produce equal number of X
bearing and Y bearing sperm.
7. Sex determination in Various
Organisms
Genotype of female Genotype of male
1. Insects XX XO
2. Drosophila XX XY
3.Birds,fish and
butterflies
WZ WW
4. Humans and other
mammals
XX XY
8. Mechanism of Sex
Determination:
1. The X-O system of sex determination operates
in insects. The male have only one X
chromosome designated as XO while the female
have two X chromosomes(XX).
2. Drosophila melanogaster have four pairs of
chromosomes. The female is XX and the male is
XY. The Y is characteristically J shape.
9. For both insect and Drosophilsa the ratio of the X
chromosome to the set of autosomes plays a key role in sex
determination.
3. The Z-W system is a form of sex determination in birds
and butterflies and some fishes. The genotype of the
female is referred as WZ and WW for male. In this system
the male is homogametic and female is heterogametic.
4. The XX/XY system is the most common sex
determination system found in humans and mammals. The
presence of Sry gene on the Y chromosome causes
maleness.
10. C0NCLUSION:
After the gametes fuse with each other during
fertilization, what factors determine whether the
resulting zygote developed into male or female?
Researchers have studied the process of sex
determination in a wide range of species and
discovered several mechanism of sex determination.
They conclude that the difference in chromosome
constitution is a mechanism for determining sex at the
time of fertilization.
