Which are the main types of numerical disorder (mutations) in the human genome? Give the genotypes.
The correct answer and explanation is:
The main types of numerical disorders (mutations) in the human genome are aneuploidy and polyploidy. These types of mutations involve changes in the number of chromosomes or parts of chromosomes. The two primary forms of these mutations are monosomy, trisomy, and tetrasomy, often leading to genetic disorders with characteristic phenotypes.
- Aneuploidy: This is a condition where there is an abnormal number of chromosomes in a cell. It can be caused by nondisjunction during cell division, leading to gametes with too many or too few chromosomes. The most common aneuploidy disorders are:
- Trisomy: This is when there is one extra chromosome in a pair. For example:
- Trisomy 21: Also known as Down syndrome, this involves having three copies of chromosome 21. Individuals with this condition typically have intellectual disabilities, characteristic facial features, and potential heart defects.
- Trisomy 18: Also known as Edwards syndrome, this involves an extra chromosome 18 and often leads to severe developmental and physical abnormalities, with many affected individuals not surviving past infancy.
- Trisomy 13: Known as Patau syndrome, this involves an extra chromosome 13 and results in severe intellectual and physical defects, often leading to death within the first year of life.
- Monosomy: This is when one chromosome in a pair is missing. A well-known example is:
- Monosomy X (Turner syndrome): This condition occurs when a female has only one X chromosome (45,X instead of 46,XX). It leads to short stature, infertility, and heart defects, but individuals can often lead relatively normal lives with appropriate medical care.
- Polyploidy: Polyploidy is the presence of more than two complete sets of chromosomes. While polyploidy is common in plants, it is rare in humans and typically not viable. However, certain instances of triploidy (three sets of chromosomes) or tetraploidy (four sets of chromosomes) can occur, often resulting in miscarriage or stillbirth.
Numerical chromosome disorders are typically diagnosed through genetic testing and can result in a range of physical and cognitive abnormalities, depending on the chromosomes involved.