Final answer:
A female who was 46 years old when she gave birth is the most likely to have a child with Down syndrome due to the increased risk of chromosomal nondisjunction with advanced maternal age.
Step-by-step explanation:
Of the options provided, the most likely to have a child with Down syndrome is C. A female who was 46 years old when she gave birth. Down syndrome, or trisomy 21, occurs when there is an extra copy of chromosome 21. The most common cause of Down syndrome is chromosomal nondisjunction during meiosis, which is an error in cell division that results in an embryo with an extra chromosome. The risk of this nondisjunction and therefore the chance of having a baby with Down syndrome increases with maternal age, especially in women over the age of 35.
The incidence of having a fetus with trisomy 21 does indeed increase dramatically with maternal age. Since the age of the male parent has less impact on the frequency of nondisjunction events, a female who was 46 years old at the time of birth is at a far greater risk compared to the younger female or the males of any age mentioned in the other options.
It's important to note, though, that individuals with Down syndrome can become successful, contributing members of society, and the decision to have a child is a deeply personal one that should be made with up-to-date information and consideration of many factors.