outlining how disorders such as Trisomy 21 occur.
Disorders such as Trisomy 21, also known as Down syndrome, occur due to chromosomal abnormalities during the process of cell division. To understand how Trisomy 21 occurs, let's first discuss some basics about chromosomes and cell division.
Our body is composed of trillions of cells, and each cell has a nucleus that contains our genetic material, which is organized into structures called chromosomes. Humans typically have 46 chromosomes, with 23 received from each parent. These chromosomes carry genes that determine various traits and characteristics.
Cell division occurs in two main forms: mitosis and meiosis. Mitosis is the process by which our body produces new cells for growth, repair, and replacement. Meiosis, on the other hand, is a specialized form of cell division that occurs in the formation of reproductive cells (sperm and egg) and leads to genetic diversity.
Now, let's focus on Trisomy 21. It is caused by an error in cell division, specifically during meiosis. Normally, during meiosis, the chromosomes pair up and then separate into two separate cells. Each resulting cell contains a single set of chromosomes, which is then combined with the other parent's single set to form the 23 pairs of chromosomes in the offspring.
In the case of Trisomy 21, an individual has an extra copy of chromosome 21, resulting in a total of three copies instead of the usual two. This additional copy of chromosome 21 occurs because of a phenomenon called non-disjunction.
Non-disjunction is the failure of chromosomes to separate properly during meiosis. As a result, one of the resulting reproductive cells (sperm or egg) ends up with an extra copy of chromosome 21. When this abnormal cell combines with a normal sperm or egg during fertilization, the resulting embryo will have 47 chromosomes instead of the usual 46, with three copies of chromosome 21.
It's important to note that the exact cause of non-disjunction leading to Trisomy 21 is not fully understood, but it is believed to occur more frequently in older parents. Additionally, there is no known behavior or environmental factor that causes Trisomy 21.
In conclusion, Trisomy 21 occurs due to a chromosomal abnormality called non-disjunction during the process of cell division. This results in an extra copy of chromosome 21, causing Down syndrome or Trisomy 21.