The number of chromosomes a child with Down syndrome has is

The correct answer is 47.

Step-by-step Explanation:

1. Normal Human Chromosome Count:
In a typical human cell, there are 46 chromosomes in total, arranged as 23 pairs. One chromosome of each pair is inherited from the mother, and the other is inherited from the father.

2. What is Down Syndrome?
Down syndrome is a genetic condition caused by an error in cell division called nondisjunction. Specifically, it is characterized by the presence of an extra copy of chromosome 21. This condition is also known as Trisomy 21.

3. Calculating the Chromosome Count:
Instead of the usual pair (2 chromosomes) at chromosome 21, individuals with Down syndrome have three copies of chromosome 21. This means they have one extra chromosome compared to the standard count.
We can express this calculation as:
$$46+1=47$$

Therefore, a child with Down syndrome has a total of 47 chromosomes.