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Chapter 1: Problem 7

What is the cause of Down syndrome?

Short Answer

Expert verified
Down syndrome is a genetic disorder that occurs when there is an extra full or partial copy of chromosome 21. This extra genetic material alters the developmental pathway and causes the characteristics we associate with Down Syndrome. The most common form is Trisomy 21, caused by abnormal cell division. Other less common forms are Mosaic Down syndrome and Translocation Down syndrome.

Step by step solution

01

Define Down syndrome

Down syndrome is a genetic disorder caused when abnormal cell division results in an extra full or partial copy of chromosome 21. This extra genetic material causes the developmental changes and physical features associated with Down syndrome.
02

Elaborate how the anomaly occurs

Down syndrome occurs when an individual has a full or partial extra copy of chromosome 21. This additional genetic material alters the course of development and causes the characteristics associated with Down syndrome. The most common form of Down syndrome is known as trisomy 21, where an individual has three copies of chromosome 21, instead of the usual two. This is caused by abnormal cell division during the development of the sperm cell or the egg cell, known as nondisjunction.
03

Mention other less common types

Apart from Trisomy 21, which accounts for 95% of cases, there are two other forms. Mosaic Down syndrome (1-2% of cases) where some cells have an extra chromosome 21 and some don't, and Translocation Down syndrome (3-4% of cases) where part of chromosome 21 is translocated (attached) to another chromosome.

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