Question

Down's Syndrome is also called Trisomy 21 because affected people have three copies of chromosome 21. How is this possible?



a
Either the sperm cell or the egg cell has two copies of chromosome 21.
b
Either the sperm cell or the egg cell has one copy of chromosome 21.
c
In a mistake in meiosis, the fertilized egg has two copies of chromosome 21.
d
In a mistake in mitosis, the fertilized egg has two copies of chromosome 21.

Answer 1

c
In a mistake in meiosis, the fertilized egg has two copies of chromosome 21.