Final answer:
Monosomy in aneuploidy is a condition where there is a loss of one chromosome from the normal diploid number in a cell, leading to severe genetic imbalance and often resulting in non-viable pregnancies.
Step-by-step explanation:
In the context of aneuploidy, monosomy refers to a condition where there is a loss of one chromosome from the normal diploid number of chromosomes in a cell.
This means that instead of having two copies of a chromosome, there is only one. In humans, euploidy corresponds to 46 chromosomes, consisting of 22 pairs of autosomes and one pair of sex chromosomes. Aneuploidy includes conditions such as monosomy and trisomy, where there are errors in chromosome number.
Monosomy occurs when a human zygote misses any one copy of an autosome, resulting in severe genetic imbalance due to insufficient gene dosage, which is often incompatible with life.
For instance, due to nondisjunction during meiosis, a gamete may lack a chromosome, and upon fertilization, the resulting zygote will be monosomic. This underscores the critical nature of gene dosage for development and survival.
While most monosomic pregnancies do not survive to birth, some aneuploid conditions involving trisomy, where an individual has an extra chromosome, can lead to viable births.
The most common and survivable trisomy is Trisomy 21, known as Down Syndrome. Individuals with Down Syndrome have a range of physical characteristics and developmental challenges, and there is an increased likelihood of a woman giving birth to a child with Down Syndrome as maternal age advances.