Question

Only nine types of aneuploids are known in newborns because

A. only nine chromosomes undergo nondisjunction.
B. most types of aneuploids are lethal early in development.
C. most aneuploids do not cause detectable defects.
D. most aneuploids do not affect the phenotype.

Answer 1

Aneuploidy refers to an error in chromosome number, with monosomy and trisomy being the two main types. Most aneuploidies are lethal to the embryo, but a few trisomic genotypes, like Down Syndrome, can survive. Chromosome abnormalities can result from segment duplications, deletions, inversions, or translocations. The correct option is B. most types of aneuploids are lethal early in development.

Step-by-step explanation:

In humans, an individual with the appropriate number of chromosomes is called euploid. Aneuploidy refers to an error in chromosome number, which includes monosomy (loss of one chromosome) or trisomy (gain of an extra chromosome).

Most aneuploidies are lethal to the embryo, although a few trisomic genotypes, like Down Syndrome, can survive. Disorders in sex chromosomes typically have milder effects because of X inactivation.

Chromosome abnormalities can also result from segment duplications, deletions, inversions, or translocations, all of which can cause problematic phenotypic effects.

Nondisjunction, the failure of homologous chromosomes or sister chromatids to separate during meiosis, is a common cause of aneuploidy. The correct option is B. Most types of aneuploids are lethal early in development.