Final answer:
The gain of a single chromosome is called trisomy. It includes conditions such as Down syndrome, which is a result of having three copies of chromosome 21. Aneuploidy encompasses both monosomy and trisomy, with trisomy 21 being the most common form that leads to live births.
Step-by-step explanation:
The gain of a single chromosome is known as trisomy. This condition results in an individual having three copies of a chromosome instead of the typical two. For example, Down syndrome is caused by having three copies of chromosome 21, which is referred to as trisomy 21. Aneuploidy describes an individual with an incorrect number of chromosomes, comprising conditions such as monosomy and trisomy. Trisomic individuals often face challenges due to an excess in gene dose from the extra chromosome. This imbalance can lead to developmental delays and other issues, though the effects vary depending on which chromosome is involved.
The term 'aneuploid' is used to describe individuals with an abnormal number of chromosomes, including both monosomy (missing a chromosome) and trisomy. The most common autosomal trisomy that results in live births is trisomy 21, the cause of Down syndrome. This genetic disorder is associated with certain physical traits, developmental delays, and is correlated with higher maternal age at the time of conception.