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?

Is it because other forms of trisomy in new borns cannot be seen due the dosage sensitive to trisonomy? Can anyone briefly explain why?

Solution

An autosome is a somatic chromosome and a normal human cell contains 23 pairs of chromosomes of which 22 pairs are autosomes and 1 pair is sex chromosomes. Any deviation from the normal set of chromosomes results in syndrome due to the presence of excess genes or deficiency of genes.

For example, the trisomy 21 results in Down syndrome, caused due to the aberration of chromosome, which results in abnormal numbers of chromosomes. The aberration of chromosome occurs when the normal egg fuses with abnormal sperm or vice versa. Children affected by Patau and Edward trisomies do not survive more than a few months, and the other trisomies are highly lethal so we do not see the newborns with other trisomies.