Short Notes For Neet Aneuploidy
Table of Contents
[Types of Aneuploidy](#Types of Aneuploidy)
[Aneuploidy Causes](#Aneuploidy Causes)
[Aneuploidy Disorders](#Aneuploidy Disorders)
Aneuploidy Meaning
Aneuploidy is a condition in which a cell or organism has an abnormal number of chromosomes. It can be caused by an error in cell division, resulting in an extra or missing chromosome.
Aneuploidy is a type of chromosomal aberration, where there is one extra or one missing chromosome. Many cancerous cells have been found to be aneuploid.
Types of Aneuploidy
Hypoploidy: When the number of chromosomes in an individual is less than the normal number (2n), such as 2n-1, 2n-2, etc.
Monosomy: When there is one chromosome less in the cells, such as in Turner’s Syndrome (XO).
Nullisomy- When there is a loss of a pair of chromosomes, i.e. 2n-2, often they do not survive.
Hyperploidy: Here there is an addition of one or more chromosomes.
Trisomy: When there is an extra chromosome in the cells, such as in Klinefelter’s Syndrome (XXY) or Down’s Syndrome (trisomy of the 21st chromosome).
Tetrasomy: There is an addition of two pairs of chromosomes, i.e. 4n.
Disomy- When a monoploid organism has one extra chromosome, i.e. n+1.
Mosaic Variegated Aneuploidy: This phenomenon, also known as Mosaicism, occurs when some cells contain an abnormal number of chromosomes.
Aneuploidy Causes
Aneuploidy is caused by non-disjunction of chromatids during cell division. When chromatids do not separate properly during mitotic or meiotic cell division, one cell ends up with an extra chromosome, while the other has one fewer chromosome. This leads to aneuploidy.
Nondisjunction occurs during Anaphase of cell division when Sister Chromatids separate.
Mosaicism is caused when nondisjunction occurs during cell division in the zygote after fertilization.
Aneuploidy and Polyploidy
Aneuploidy is different from polyploidy, which is characterized by an increase in one or more complete sets of chromosomes. This happens when cytokinesis does not follow karyokinesis and is common in plants, such as triploid and hexaploid.
Euploidy is also referred to as variation in the complete sets of chromosomes, i.e. multiple of haploid sets of chromosomes. Euploidy above the number of diploid cells is termed as polyploidy.
Aneuploidy Disorders
Aneuploidy in humans leads to various chromosomal disorders such as miscarriages, which account for 1 in 160 live births. Trisomy is the most common aneuploidy disorder. Some of the common diseases associated with it are listed below.
Down’s Syndrome: Trisomy of the 21st Chromosome
Edward’s Syndrome - Trisomy of the 18th Chromosome
Patau Syndrome: Trisomy of the 13th Chromosome
Klinefelter’s Syndrome - Individuals with this condition have an additional number of the X chromosome, XXY.
Turner’s Syndrome - One X chromosome is missing, resulting in an XO genotype.
Frequently Asked Questions
What are aneugens?
Aneugens are a type of chemical or physical agent that can cause mutations in a cell’s DNA.
Aneugens are agents that can lead to aneuploidy. Many mutagenic carcinogens are classified under this term, such as X-rays, pesticides, and chemicals like colchicine, etc.
Tetrasomy and Pentasomy
Tetrasomy and pentasomy are types of chromosomal abnormalities in which a person has one extra chromosome in each cell. In tetrasomy, the person has four copies of one chromosome, while in pentasomy, the person has five copies of one chromosome. These conditions can cause a variety of physical and mental health problems.
The presence of four or five copies of a chromosome is referred to as tetrasomy and pentasomy respectively. This is a common occurrence in sex chromosomes or allosomes and can lead to chromosomal disorders such as XXXX, XXXXY, XXYY, XYYYY and XXXXX.
