Sex Determination

From The School of Biomedical Sciences Wiki
Revision as of 16:28, 30 November 2012 by 120203626 (Talk | contribs)
Jump to: navigation, search

Sex Determination is the process by which two sexes, male and female, become into being. It determines the development of the sexual organs of the organism.

Protenor Mode:

Otherwise known as the XX/XO mode of sex determination.

The presence or absence of the X chromosome in male gametes determines sex. Females are the homogametic sex (XX). Males only have one chromosome (X) and are represented by XO - they act as the heterogametic sex. Examples include: some insects such as cockroaches and grasshoppers[1].

Lygaeus Mode:

The more common mode of sex determination: XX/XY.

There must be the presence of a Y chromosome in order to determine the male sex. In humans there is a area, found on the Y chromosome, called the Sex Determining Region Y determines maleness. When this is present it activates the formation of testes thanks to a conformational change in the DNA due to a change in the level of gene expression[2]. Individuals that have a Y chromosome will become males independent of the number of X chromosomes[3]; genetic disorders such as Klinefelter syndrome are caused by to the presence of extra X chromosomes in an individual with a Y chromosome. Often in this mode the females are homogametic (having two X chromosomes and consequently producing only one type of gamete, X), and the males are heterogametic ( having one X and one Y chromosome and consequently producing two types of gametes, X or Y)[4]. Examples of organisms using this form of sex determination include: most mammals, including humans, as well as some insects.

Although in mammals, etc, the heterogametic sex is male, in birds it is the female sex that is heterogametic and the male that is homogametic. 

References:

  1. http://www.tutorvista.com/content/biology/biology-iii/chromosomes/sex-determination.php
  2. http://www.ncbi.nlm.nih.gov/books/NBK22246/
  3. Alberts. B, Johnson. A, Lewis. J, Raff. M, Roberts. K, Walter. P, (2008), Molecular Biology of the cell, fifth edition, New York, Garland Science.
  4. http://www.tutorvista.com/content/biology/biology-iii/chromosomes/sex-determination.php
Personal tools
Namespaces
Variants
Actions
Navigation
Toolbox