There are only three autosomal trisomic conditions Patau Edw

There are only three autosomal trisomic conditions (Patau, Edward, and Down syndrome) where a fetus will survive to birth. why do we not see other forms of trisomy in newborns?

Solution

Generally, trisomic conditions related to sex chromosomes (e.g. klinefelter\'s) are not that drastic compared to autosomal trisomic conditions , because aberrant gene is usually compensated in either as Y-chromosome( smallest )or X-chromosome inactivation. But, unlike this, autosomal chromosomes are crucial for development and in most trisomic cases result into misscarriages or still birth.

If examined closely, Edward\'s (chromosome 21) ,Edward\'s (chromosome 18 ;1 in 8000) and Patau\'s (chromosome 13 ; 1 in 19000) are most prevalent to least occuring birth trisomic defects in population.It highlights that body only accommodates trisomy of chromosomes that are smaller in size and such fetus survive till birth. Adding together Large chromosomes in animals is usually detrimental and results into death.