We asked this question to Genetic Engineer Dilara Sarı. He enlightens hundreds of thousands of people by sharing about genetic research, biological systems and scientific developments on Instagram, Twitter and YouTube.
This time, as a guest of Webtekno, he will enlighten many of our readers about an important genetic science. Here are our questions and Dilara’s answers:
Why do people with Down syndrome have 47 chromosomes instead of 46?
Individuals without any chromosomal abnormalities have a total of 46 chromosomes, 1 pair of these chromosomes are sex chromosomes. That is, there are 22 pairs of autosomal chromosomes. The condition of these chromosome pairs being triple instead of double is called trisomy. Down syndrome is usually a trisomy on the 21st chromosome, that is, a triplet, so individuals with Down syndrome have 47 chromosomes, not 46.
There are different types of Down syndrome. What exactly are the differences between them?
In the case of mosaic Down syndrome, there are actually 46 chromosomes in the first fertilization, while some cells have 47 chromosomes due to an anomaly that develops later. Some cells of the person carry 46 chromosomes and some cells carry 47 chromosomes. The regions where 47 chromosomes are most prominent are the regions most affected by the syndrome. For example, if 46 chromosomes are observed in the cells in the nervous system, not 47, the IQ level of the person may not be affected by the syndrome and may develop the same as their peers. If 47 chromosomes are observed in the muscular system, posture and speech disorders will be observed.
Translocation Down syndrome is the rarest type of Down syndrome, constituting 3% of cases. In other varieties, the extra chromosome/chromosome part is located next to the 21st chromosome pair, but in the case of translocation, this excess is free and adheres to the chromosome pair.
So what causes the similar physical appearance?
Cells contain extra genetic material. This excess material creates unique physical deformations and developmental problems, as in other anomalies, and affects the external appearance of the individual.
For Down syndrome, the extra genetic material in this 21st chromosome creates a physical change by preventing the development of certain connective and bone tissues, especially in the head area. A small nose, mouth and ears, almond eyes, short neck, rounded head shape from the back (up from the nape), short nails, and white spots on the iris are the most physically noticeable features.
At the same time, these individuals are more prone to gain weight due to muscle movement problems. In fact, individuals with Down syndrome all have different skin, hair and eye colors and are different from each other. The fact that the excess of the 21st chromosome causes such changes, especially in the head region, causes all individuals with Down syndrome to resemble each other.
We have said that in mosaic Down syndrome, there is a change on the basis of the cell and system it affects. In other words, individuals with Mosaic Down syndrome may have less physical symptoms compared to the normal and translocation type, and the symptoms vary depending on which system is affected. For this reason, their facial features may not resemble other Down syndrome individuals too much.
Thanks to Dilara Sarı for answering our question. You can also follow him on his social media accounts: Instagram | Twitter | YouTube
Dilara will soon answer our other questions about genetics. Stay tuned…
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