Down syndrome is a common disorder.Which of the following circumstances results in Down syndrome?
A)Defective,recessive alleles
B)Defective,dominant alleles
C)Insufficient number of chromosomes
D)Extra chromosome

Question

Quizplus · Accepted Answer

Down syndrome results from an individual having an extra copy of chromosome 21, also known as trisomy 21. This occurs as a result of a nondisjunction event during meiosis, in which the chromosomes fail to separate properly. It is not caused by defective alleles or an insufficient number of chromosomes.

Down Syndrome Is a Common Disorder