Question

Down’s syndrome is due to
a) Crossing over
b) Linkage
c) Sex linked inheritance
d) Nondisjunction of chromosomes

Answer 1

Hint: Down's Syndrome is a genetic disease caused by irregular cell division, which results in an excess of genetic material on chromosome 21. Physical and mental retardation and disability result as a result of this.

Complete answer:
Down's Syndrome (also known as trisomy 21) is a disorder in which an infant is born with an extra copy of his 21st chromosome. In all reproduction cases, both parents pass their genes on to their children. These genes are transmitted in chromosomes.
When daughter cells develop, each cell is expected to receive 23 pairs of chromosomes, for a total of 46 chromosomes. The mother contributes half of the chromosomes, while the father contributes the other half.
In children with Down syndrome, one of the chromosomes is not properly separated. Instead of two copies of chromosome 21, the infant has three copies, or an additional partial copy. As the brain and physical features grow, this extra chromosome causes complications.
Down's Syndrome does not occur due to crossover, linkage, and is not linked to sex.
Most of the time, Down Syndrome is not inherited. It is caused by a cell division error during the early development of the foetus.
Translocation of Down syndrome can be passed down from parent to child. However, only about 3 to 4 percent of children with Down syndrome have translocation, and only some of them have inherited it from one of their parents.

The correct answer is option (D) Nondisjunction of chromosomes.

Note:
Down syndrome screening is done as part of regular prenatal treatment. You can have an exam if you're a woman over 35, your child's father is over 40, or you have a family history of Down Syndrome. Evaluation of ultrasound and blood tests may look for Down syndrome in your foetus in the first trimester.An ultrasound and quadruple marker screen (QMS) test can help to detect Down syndrome and other defects in the brain and spinal cord. This test is performed between 15 and 20 weeks after pregnancy.