Aneuploidy is a disruption in an organism’s normal number of chromosomes, which can cause serious birth defects and congenital conditions. It is caused by an error in meiosis and can be recognized during prenatal testing. Trisomy and monosomy are two types of aneuploidy.
Aneuploidy refers to a disruption in an organism’s normal number of chromosomes. Many serious birth defects and congenital conditions are linked to aneuploidy, as chromosomes are the repository for DNA, a crucial component of life. In many cases, a fetus with aneuploidy will miscarry before it is fully developed, and in others, the organism may have difficulty surviving after birth. In other cases, the aneuploidy represents a handicap, but the organism is able to live a happy and healthy life despite the challenge.
Humans typically include aneuploidy testing in their routine prenatal testing. If an aneuploidy is identified, parents are warned of problems their child may encounter. In some cases, parents choose to terminate the pregnancy if the aneuploidy is associated with severe disabling birth defects that would make the baby’s life short and unpleasant.
The causes of aneuploidy are not fully understood, but the mechanisms are. Aneuploidy is caused by an error in meiosis, the division of cells to create gametes. A gamete is a cell that normally has a haploid set of chromosomes, meaning it contains 50% of the genetic information of the parent organism. When a gamete joins a gamete from another organism, a complete set of chromosomes is created and it develops into a whole new organism.
The first step in meiosis involves duplicating a cell into two complete copies. Each copy then splits in two, creating four cells from the original parent cell. When the chromosomes in a cell fail to divide completely, the daughter cell can end up with an extra chromosome within a haploid set. When the gamete joins another gamete, the resulting condition is trisomy, which means that one of the pairs of chromosomes has turned into a triad.
If, on the other hand, a chromosome is deleted or damaged, the condition is known as monosomy. Monosomy refers to the fact that one of the chromosomes in an otherwise diploid set is unpaired. In humans, this would mean that the baby has only 45 chromosomes instead of the normal 46, or that one of the chromosomes in a pair is badly damaged.
These chromosomal disorders can be easily recognized during prenatal testing, as the chromosomes can be easily stained and counted. Genetic conditions are linked to specific chromosomes; trisomy 21, for example, refers to an extra copy of the 21st chromosome, resulting in Down syndrome.
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