Question

13. Assume that karyotyping cells from a human tumor reveals that they are tetraploid. How many total chromosomes would be present in these cells?

14. Assume that, instead, karyotyping cells from a human tumor reveals that they each have 47 chromosomes. How would these cells be classified based on the terminology for variant chromosome numbers?

15. A reciprocal translocation occurs between chromosomes 13 and 15 in a human oogonium. Assuming that adjacent segregation occurs during oogenesis, what is the expected probability that the resulting ovum would be capable of producing viable offspring following fertilization?

Answer 1

13. The total number of chromosomes in that case = 92.

14. This is a condition of aneuploidy. In this case, the patients have an extra full copy of chromosome 21 and the normal 46 chromosomes, altogether 47.  

15. Reciprocal translocation between chromosomes 13 and 15 is a rare event. It is a case of rare balanced non-Robertsonian Translocation (RT). Normally acrocentric chromosomes 13, 15, 22 etc. are found as RT. In balanced RT, 50% cases of abortion and another 20% is seen with children with abnormal genetic makeup. In this case of balanced non-RT, the satellite of chromosome 13 is translocated to 15 and some part of 15 is translocated to 13. The outcome of normal or unbalanced gamates depend on the location of breakpoints and also on the quadrivalent configuration of chromosomes in the pachytene stage. Balanced translocations may lead to reproductive error. Cytognetic analysis is the primry method for analysis of chromosomal abnormalities.