Question

Down’s syndrome in humans is due to

• A. three copies of chromosome 21
• B. three ‘X’ chromosomes
• C. two ‘Y’ chromosomes
• D. monosomy

Answer 1

The correct option is A

three copies of chromosome 21

The correct option is A

Explaination of the correct answer:

1. Every cell in the human body has a nucleus, which stores genetic information in the form of genes. Genes are arranged along rod-like structures called chromosomes and carry the codes for all of our inherited features. each cell's nucleus typically includes 23 chromosomal pairs, half of which are inherited from each parent. when a person has a whole or partial extra copy of chromosome 21, they are diagnosed with Down syndrome.
2. This extra genetic material disrupts the path of development, resulting in the Down syndrome traits. Low muscle tone, short stature, an upward slant to the eyes, and a single deep groove across the center of the hand are some of the physical characteristics of Down syndrome, though each person is unique.
3. The trisomy of chromosome 21 is what causes own's syndrome. nondisjunction of chromosomes during meiosis during gamete production is the most common reason.
4. Trisomy 21: Most of the time, trisomy 21—in which a person has three copies of chromosome 21 instead of the typical two copies—causes Down syndrome. This results from sperm or egg cell development that results in aberrant cell division.

The explanation for the incorrect options:

Option B:

1. Three ‘X’ chromosomes: A condition that causes some girls to have an extra X chromosome.
2. Triple X syndrome is typically brought on by an abnormal egg or sperm cell or by a mistake made early in the development of the embryo.
3. Few or no symptoms are present in many women. Most of the time, no therapy is necessary. Learning impairments and developmental delays may necessitate intervention, such as counseling.

Option C:

1. Two ‘Y’ chromosomes: A male who possesses an extra Y chromosome has XYY syndrome, sometimes referred to as Jacobs syndrome, which is an aneuploid genetic disorder.
2. An extra Y chromosome results in the rare chromosomal abnormality known as XYY syndrome.
3. One X and one Y chromosome are among the 46 chromosomes that males typically have. Two of the 47 chromosomes present in XYY syndrome-affected males are Y chromosomes.

Option D:

1. Monosomy: In contrast to the two copies typically found in diploid cells, monosomy refers to the circumstance in which only one of a pair of chromosomes is present in cells.
2. In the instance of single monosomy, it refers to the absence of one chromosome from a pair, leaving a clone with 45 chromosomes.

Final Answer: Down syndrome is caused by trisomy 21.