Question

Familial Down syndrome is similar to primary Down syndrome in that it is caused by trisomy 21. However, in familial Down syndrome, all or part of the third copy of chromosome 21 has translocated onto another autosome, typically chromosome 14. In cases of familial Down syndrome, one of the parents of the affected child is often a carrier of a translocated chromosome. The translocation carrier parent does not have Down syndrome because he or she has a total of two copies of chromosome 21.Suppose that a woman is a translocation carrier of chromosome 21 on chromosome 14. She conceives six zygotes with a normal man who carries no aneuploidies. Match the description of the chromosomes inherited by each zygote with the viability of the zygote.

Answer 1

Viable Normal or Translocation carrier,there are;

- Two normal copies of 14 and two normal copies of 21.

- One normal copy of 14 and one normal copy of 21, then one 14 to 21 translocation.

Then viable with down syndrome will include:

- One 21 to 14 Translocation, two normal copies of 21 and one normal copy of 14.

Then the VIABLE with down syndrome will be:

- One normal copy of 14 with two normal copies of 21

- Two normal copies of 14 with one normal copy of 21

- One 21 to 14 Translocation,a normal copy of 21,then two normal copies of 14.