There are only three autosomal trisomic conditions (Patau, Edward, and Down Syndrome) where a fetus will survive to birth. Why do you think this is so?

An autosomal trisomic condition is the deviation of the chromosome number where an extra copy of the chromosome present with the chromosome pair. The three trisomic conditions are Patau - extra copy at chromosome 13, Edward - extra copy of chromosome 18, and Down Syndrome - an extra copy of chromosome 21

Children or fetuses affected by these trisomies show the least life expectancy and develop as mentally week, other than these trisomies other trisomic conditions are highly lethal so we do not see the survivors and it is due to dosage sensitivity which means that increasing or decreasing their expression levels will reduce cell viability.

step 1: nitrogen fixation- conversion of atmospheric no₂ into forms useful to plants by lightning, bacteria, and cyanobacteria.

step 2: nitrification-process of converting ammonia to nitrite or nitrate.

step 3: assimilation-plant roots absorb new form of nitrogen.

step 4: ammonification-conversion of organic nitrogen to ammonia by bacteria involved in decomposition.

step 5: denitrification-bacteria turns the decomposed matter back into n₂o, which is released into atmosphere; repeat cycle.