SEX DETERMINATION–by CHROMOSOMES
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Sex is decide by chromosomes in general. But in some organisms environment and hormones will decide sex.
The organisms produce eggs are called females. The organisms produce sperms are called males. “Henking” found in some insects two types of sperms. Some sperms show an element and other is lacking that element. This difference is essential for sex determination miss Stevens gave complete account of chromosomal basis of sex determination’ she named the X & “Y” chromosome allosomes and other chromosomes as autosomes. 
Allosomes: These chromosomes will carry genes for sex. They are ‘X’ , Y chromosomes.
Autosomes: The remaining chromosomes of nucleus are called autosomes. They carry genes for vegetative characters.
SEX DETERMINATION OF CHROMOSOME BASIS
XX-XY TYPE SEX DETERMINATION This is also called
Lygaens type. This was described by Willson & Steuns.
a) XX FEMALE AND XY MALE Ex: Drosophila, man. The total number of chromosomes in four pairs,.
The male shows XY” allosomes. Tow types of sperms are formed.
a) ‘X bearing b,) Y bearing. Sex is decided by the fertilizing sperm.
Sex Determination in Man
Sex Determination in Drosophila
b) XY female XX Male: Ex Birds, moths; butterfly.
In these animals Q is also represented by “2’ (XX or zz-male). The female Is “XY” or “ZW” Ex: Bird.
The male “XX” and female” XY”. The sex Is decided by the type of egg which is fertilized.
2) Protenor Type or ‘XX’ Female and ‘XO’ Male:
Ex: Squash bug (Anasa)
1) Autosomes
2) XChromosome
Ex: Gross hopper. In these animals sex is decided by aullosomes. The male has only one X chromosome. In the female 2X chromosomes are present.
Ex: Anasa. The 20 autosomes and one X Chromosome shows monosome (21). The female has 20 autosomes and 2X chromosomes. (20+2= 22).
DIPLOID FEMALES AND HAPLOID MALES-
This Is also called Hymenopter type of sex determination.
Ex: Honey bee, wasp, ant.
In these individuals three types are recognised.
1) Diploid Queen : Fertilized eggs will develop into fully developed functional females.
2) Diploid workers: They developed from fertilized eggs. They are under developed.They are non functional females
3) Haploid Drones (Males): These are developed from haploid unfertilized eggs. They are functional males. They can produce sperms.
previous topic Inter action of genes and
sex determination by Genes-Environment-hormones.
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