Chapter 21, Problem 41A

Summary Introduction

To write:

The cause of Down Syndrome.

Introduction:

During cell division, the separation of chromosomes take place with each of the sister chromatids going to the opposite poles of the cell. Thus, each new cell has the right number of chromosomes. The cell division where the sister chromatids do not separate properly is known as nondisjunction. Nondisjunction can happen in any organism where gametes are produced through meiosis. In humans, alterations of chromosomes are associated with serious disorders.

Explanation of Solution

Down syndrome is one of the earliest known human chromosomal disorders. It is caused by an excess of chromosome 21 and is also called trisomy 21. The characteristics of down syndrome includes distinctive facial features like flattened face and small head, short neck, short stature, heart defects and mental disability. The frequency of Down syndrome increases with the age of the mother. Studies show that the risk of having a child with Down syndrome is about 6 percent in mothers who are 45 years and older.

Conclusion

Down syndrome is one of the earliest known human chromosomal disorders. It is caused by an excess of chromosome 21.