Describe normal embryo formation and two mechanisms of nondisjunction represented in the figure and identify the consequences of these chromosomal anomalies
ANSWER: The figure represents uniparental disomy, which can be produced by several mechanisms
involving nondisjunction. (a) Normal chromosomal configuration where gametes contain o copy of each chromosome and fertilization produces a zygote carrying two copies of a
chromosome—one derived from each parent. (b) Nondisjunction in both parents, in which
one gamete carries both copies of a chromosome and the other gamete is missing a copy of
that chromosome. Fertilization produces a diploid zygote, but both copies of one
chromosome are inherited from a single parent. (c) Nondisjunction in one parent, resulting in
the loss of a chromosome. This gamete fuses with a normal gamete to produce a zygote
monosomic for a chromosome. An error in the first mitotic division results in duplication of
the monosomic chromosome, producing uniparental disomy
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