Biology SEX DETERMINATION

### XX/XO TYPE SEX DETERMINATION

● Further investigations by other scientists led to the conclusion that the color{Violet}"X body" of color{Violet}"Henking" was in fact a chromosome and that is why it was given the name color{Violet}"X-chromosome".

● It was also observed that in a large number of color{Violet}"insects", the mechanism of sex determination is of the color{Violet}"XO type", i.e., all eggs bear an color{Violet}"additional X-chromosome" besides the other chromosomes (autosomes).

● On the other hand, some of the color{Violet}"sperms" bear the color{Violet}"X-chromosome" whereas color{Violet}"some do not".

● Eggs fertilised by sperm having an color{Violet}"X-chromosome" become color{Violet}"females" and, those fertilised by sperms that color{Violet}"do not" have an color{Violet}"X-chromosome" become color{Violet}"males".

● Due to the involvement of the X-chromosome in the color{Violet}"determination of sex", it was designated to be the color{Violet}"sex chromosome", and the rest of the chromosomes were named as color{Violet}"autosomes".

● color{Violet}"Grasshopper" is an example of color{Violet}"XO" type of sex determination in which the males have only one X-choromosome besides the autosomes, whereas females have a pair of X-chromosomes.

● These observations led to the color{Violet}"investigation" of a color{Violet}"number of species" to understand the mechanism of sex determination.

### ZW/ZZ TYPE SEX DETERMINATION

● In some other organisms, e.g., color{Violet}"birds" a different mechanism of sex determination is observed .

● In this case the total color{Violet}"number of chromosome" is same in both color{Violet}"males and females".

● But color{Violet}"two different" types of gametes in terms of the sex chromosomes, are produced by females, i.e., color{Violet}"female heterogamety".

● In order to have a color{Violet}"distinction" with the mechanism of sex determination described earlier, the two different sex chromosomes of a color{Violet}"female bird" has been designated to be the color{Violet}"Z and W chromosomes".

● In these organisms the females have color{Violet}"one Z and one W" chromosome, whereas males have a color{Violet}"pair of Z-chromosomes" besides the autosomes.

### SEX DETERMINATION IN HUMANS

● It has already been mentioned that the color{Violet}"sex determining mechanism" in case of color{Violet}"humans is XY" type.

● Out of 23 pairs of chromosomes present, color{Violet}"22 pairs" are exactly color{Violet}"same" in both males and females; these are the color{Violet}"autosomes".

● A color{Violet}"pair of X-chromosomes" are present in the female, whereas the presence of an color{Violet}"X and Y chromosome" are determinant of the male characteristic.

● During color{Violet}"spermatogenesis" among males, color{Violet}"two types" of gametes are produced.

● color{Violet}"50 per cent" of the total sperm produced carry the color{Violet}"X-chromosome" and the rest color{Violet}"50 per cent" has color{Violet}"Y-chromosome" besides the autosomes.

● Females, however, produce only color{Violet}"one type of ovum" with an X-chromosome.

● There is an color{Violet}"equal probability of fertilisation" of the ovum with the sperm carrying either X or Y chromosome.

● In case the ovum fertilises with a sperm carrying color{Violet}"X-chromosome" the zygote develops into a color{Violet}"female (XX)" and the fertilisation of ovum with color{Violet}"Y-chromosome" carrying sperm results into a color{Violet}"male offspring".

● Thus, it is evident that it is the color{Brown}"genetic makeup of the sperm" color{Violet}"that determines the sex of the child".

● It is also evident that in each pregnancy there is always color{Violet}"50 per cent probability" of either a male or a female child.

● It is unfortunate that in our society color{Violet}"women are blamed" for producing female children and have been ostracised and ill-treated because of this false notion.