Question

Trisomy 21 can be caused by nondisjunction of chromosome 21, or by inheriting a Robertsonian fusion of chromosome 21 attached to chromosome 14. Suppose an individual is a carrier for this Robertsonian fusion, as seen below. How many different gametes can this individual produce?

Answer 1

6 in total; 3 viable and 3 non-viable

Step-by-step explanation:

Robertsonian translocation is one of the types of structural alteration in chromosomes, in other words, a rearrangement between chromosomes, which can occur between five pairs of acrocentric chromosomes (chromosomes with the centromere close to the end of one of the "arms"): 13, 14, 15, 21 and 22.

An individual who has Robertson's translocation between chromosomes 14 and 21 generally has only 45 chromosomes.

In addition, a carrier of this type of translocation can theoretically produce 6 types of gametes, however 3 of them are not viable.

As for the three remaining gametes: One is normal, and among the other two, one is balanced and the last is unbalanced.

So, theoretically, when combining a normal gamete, the probability of a child with down syndrome being born through these conditions is 1/3 (considering that the probability of producing a certain type of gamete is equal for the three types).