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Can changes in the number of chromosomes affect health and development?
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Mutationsanddisorders

Can changes in the number of chromosomes affect health and development?

Human cells typically contain 46 chromosomes, and any gain or loss in this number can significantly impact growth, development, and bodily function.

Overview

Human cells normally contain 23 pairs of chromosomes, for a total of 46. A change in the number of chromosomes can cause problems with growth, development, and the function of the body's systems. These changes can occur during the formation of reproductive cells (eggs and sperm), in early fetal development, or in any cell after birth. A gain or loss in the number of chromosomes from the normal 46 is called aneuploidy.

Types of Chromosomal Changes

Trisomy

A common form of aneuploidy is trisomy, or the presence of an extra chromosome in cells. People with trisomy have three copies of a particular chromosome in cells instead of the normal two. Down syndrome (also known as trisomy 21) is an example of a condition caused by this; people with Down syndrome typically have three copies of chromosome 21 in each cell, for a total of 47 chromosomes per cell.

Monosomy

Monosomy, or the loss of one chromosome in cells, is another kind of aneuploidy. People with monosomy have one copy of a particular chromosome in cells instead of the normal two. Turner syndrome (also known as monosomy X) is a condition where women usually have only one copy of the X chromosome in every cell, for a total of 45 chromosomes per cell.

Extra Sets of Chromosomes

Rarely, some cells end up with complete extra sets of chromosomes:

  • Triploidy: Cells with one additional set of chromosomes, for a total of 69 chromosomes.
  • Tetraploid: Cells with two additional sets of chromosomes, for a total of 92 chromosomes.

A condition in which every cell in the body has an extra set of chromosomes is not compatible with life.

Chromosomal Mosaicism

In some cases, a change in the number of chromosomes occurs only in certain cells. When an individual’s cells differ in their chromosomal makeup, it is known as chromosomal mosaicism. This occurs from an error in cell division in cells other than eggs and sperm. Most commonly, some cells end up with one extra or missing chromosome, while other cells have the usual 46. Mosaic Turner syndrome is one example, where some cells have 45 chromosomes due to a missing X chromosome, while others have the usual number.

Cancer and Chromosomes

Many cancer cells also have changes in their number of chromosomes. These changes are not inherited; they occur in somatic cells (cells other than eggs or sperm) during the formation or progression of a cancerous tumor.

Frequently Asked Questions

Turner syndrome can be suspected when a girl has short stature, amenorrhea, or infertility, but many have subtle features. A definitive diagnosis is made through a chromosomal analysis (karyotype) that shows only one X chromosome. Hormone testing and imaging of the ovaries may also be part of the work‑up.
Parents often notice a combination of features such as a flattened facial profile, upward slanting eyes, a small mouth, and low muscle tone (hypotonia). Early developmental delays, especially in speech and motor skills, are also common. If several of these signs appear, a pediatrician may recommend a karyotype test to confirm the diagnosis.
Triploidy is usually lethal, with most pregnancies ending in miscarriage or stillbirth. In rare cases where the pregnancy continues, the infant is often born with severe growth restriction, multiple congenital anomalies, and a very low chance of long‑term survival. Parents are offered counseling and options for pregnancy management.
While many chromosomal abnormalities occur randomly, certain measures can lower risk: maintaining a healthy weight, avoiding smoking and excessive alcohol, managing chronic conditions like diabetes, and receiving prenatal care early. For women over 35, options such as pre‑implantation genetic testing (PGT) with IVF can screen embryos for chromosomal normalcy before implantation.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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