Classification of the mechanism of definition of the sex.

Date: 2015-10-07; view: 467.

In the cells of diploid organisms, with separate sexes, a specific pair of chromosomes determines the sex of the individual. They are called sexchromosomes. All other chromosomes are termedautosomes. The two members of each pair of homologous autosomes are similar in size and shape, but this may not be true of sex chromosomes.

In mammals including man and most insects including fruit fly, one sex chromosome is smaller than the other in the males. The larger one is known asX chromosome and the smaller one asY chromosome. The female of these animals has a pair of X chromosomes. Thus, the condition for the male may be briefly expressed as XY and that in the female as XX. The similar and dissimilar sex chromosomes of females and males are described ashomomorphic andheteromorphic respectively. Though different in size and shape, the X and Y-chromosomes act as homologous chromosomes in meiosis; they pair, separate and pass into different gametes.

The female of many vertebrates (fishes, reptiles, birds) and some insects (butterflies, moths) has heteromorphic sex chromosomes and male has homomorphic sex chromosomes.

There are another mechanisms of sex determination. For example:

- One sex has one sex chromosome only, but another sex has two sex chromosomes. For instance Order Hemiptera (bugs).

- One sex is diploid another sex is haploid. Honey bee for instance.

- The sexes are determined correlation of number of kits Sex Chromosomes and Autosomes.