Question

Down syndrome is a genetic disorder in humans caused by having three copies of chromosome 21 in their cells. Based on the information in the passage, how could a person with this disorder have gotten an extra copy of this chromosome? A.replication of chromosome 21 after meiosis B.nondisjunction of chromosome 21 during meiosis C.crossing over of chromosome 21 with other chromosomes D.recombination of chromosome 21 with other chromosomes

Answer 1

Down syndrome is caused by the presence of an extra copy of chromosome 21 due to nondisjunction during meiosis.

Step-by-step explanation:

A person with Down syndrome could have gotten an extra copy of chromosome 21 due to nondisjunction during meiosis. Nondisjunction is an error that can occur when the paired chromosomes fail to separate properly during cell division.

The result of nondisjunction during meiosis can lead to one gamete receiving two copies of chromosome 21 and the other receiving none. When the former fuses with a normal gamete from the other parent, the resulting zygote ends up with three copies of chromosome 21, causing Down syndrome.

The spindle checkpoint is a control mechanism within the cell that ensures chromosomes are properly attached to the spindle fibers before proceeding with cell division. If there is a problem with this checkpoint, chromosomes may not align properly and fail to separate correctly resulting in nondisjunction.