Although in humans there are 22 pairs of autosomal chromosomes, only three different chromosomal trisomies are commonly seen in newborns. of the remaining 19 autosomes, many trisomies have not been seen in newborns. why not?

trisomy for the other autosomal chromosomes is often lethal, and the affected embryos are miscarried. trisomy for these other autosomal chromosomes occurs so rarely that it has never been documented. trisomy for these autosomal chromosomes has no effect and therefore would never be noticed. these autosomal chromosomes do not contain the same type of dna or protein that makes up chromosomes susceptible to trisomy.

The answer is; Trisomy for the other autosomal chromosomes is often lethal, and the affected embryos are miscarried

Most trisomy that occurs involves sex chromosomes. This is because the Y chromosome (that codes for male gender) carries very few genes to have enormous implications in males in case of mutations or nondisjunction. In females, X chromosome occurs in pairs where one is silenced. Trisomy in these is not lethal. Trisomy in other critical chromosomes result in improper development of fetus and is unable to develop normally to birth.  

you know they are heterozygous for a trait because they have it as jj or jj.

the correct answer is option d.

an appositive is a noun, noun phrase or noun clause which follows another noun or noun phrase in order to describe it or name it another way. they are usually used between commas, brackets or dashes.

the example sentence with the correct use of commas is the following:

her uncle, the man over there in the red shirt, owns the hardware store in town.