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The genetics behind down syndrome

A genetic disorder is generally described as a disease caused completely or by a change in the DNA sequence. The different causes of genetic disorders are monogenic, where a mutation in one particular gene has taken place, or multifactorial inheritance disorder, where there are mutations in multiple genes. Furthermore, they can be caused by a combination of gene mutations and environmental factors, or by damage to chromosomes.

As scientists unpack and study the human genome, they have discovered that a genetic component is present in all but a few diseases. Some diseases are caused by mutations that are inherited at birth, whilst others are caused by acquired mutations that occur during an individual’s lifetime. These are not inherited by parents but instead, occur randomly due to some environmental exposure.

What is Down Syndrome?

Down syndrome is a condition in which a person has an extra chromosome. Typically, a baby is born with forty-six chromosomes, however, babies with Down syndrome have an extra copy of one of the chromosomes - chromosome 21. This extra copy changes how the baby’s body and the brain are able to develop, which results in both physical and mental challenges.


Down syndrome generally causes learning difficulties, mental retardation, a characteristic facial appearance, and poor muscle tone in infancy, which is also known as hypotonia. Through having Down syndrome, individuals also have an increased risk of heart defects, digestive problems, and hearing loss. People with

Down syndrome have low activity of the

thyroid gland as well, which is an organ in the lower neck that produces hormones.

IS down syndrome inherited?

In most cases, Down syndrome is not inherited, but rather occurs at random instances when the reproductive cells are formed. If there is an error in cell division, something called nondisjunction happens which results in the reproductive cells to have an abnormal number of chromosomes. For example, an egg or sperm cell could possibly gain an extra copy of chromosome 21. If one of these atypical reproductive cells contributes to the genetic makeup of a child, the child will then have an extra chromosome 21 in each of the body’s cells.

By Akshita Malhotra

(Year 12 Student at Bangkok Patana School)


“Facts about Down Syndrome.” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention, 5 Dec. 2019, [Accessed October 2020]

“About Down Syndrome.”, [Accessed October 2020]

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