2. A likely explanation for an abnormal human phenotype associated with a trisomy is: A) the presence of multiple recessive mutant alleles. B) the extra chromosome has typically undergone significant rearrangements. C) the absence of genes necessary for certain cellular processes. D) altered gene dosage (also known as genetic balance). E) the random inactivation of a complete autosome.

Trisomy is a type of aneuploidy which is characterized by the presence or occurance of an extra copy of a particular chromosome.As a result the chromosomes in which the trisomy is occurring contain 3 arms instead of 2. Trisomy occur due to non disjunction of a particular chromosome during meiosis.

As a result a second copy of chromosome is present inside the cell containing that abnormal chromosome.If the same thing occur in the cell of gamet undergoing fertilization then there is a high chance that the embryo will carry that extra chromosome.

In case of humans Trisomy result in the rearrangement extra chromosome which ultimately give rise to

1 Trisomy 18 occur due to extra copy of chromosome no 18

2 Trisomy 13 occur due to extra copy of chromosome no 13

3 Trsomy 21 occur due to extra copy of chromosome no 21 which is also called down syndrome.