Question

Of the three children born to a young mother of 25 years, two of them showed symptoms of Down syndrome. Karyotyping (analysis of chromosomes) of the children with Down syndrome showed 46 chromosomes! Provide an explanation for this observation. If you were to determine the karyotype of the parents, how many chromosomes would you expect to find (you should list chromosome # of both parents? Explain.

Answer 1

Down syndrom is the result of trisomy in 21st chromosime of human beings. In 4% of the down syndrom cases, the syndrom occures due to translocation of chromosomes where the number of chromosomes remains 46, instead of 47 in the other cases. Here the additional chromosomes will be attached to the 14th chromosomes and this produces the symptoms.

In this case the number of chromosomes in both the parents will be normal. i.e In male it is 45+XY and female it is 45+XX.