An individual with an extra copy of a chromosome is described as having what?

• A. Trisomy
• B. Polyploidy
• C. Nondisjunction
• D. Genetic Engineering

Answer: (A)

Trisomy refers to having three copies of a particular chromosome in a cell. In humans, normal cells are diploid with two copies of each chromosome, so when one chromosome is present in three copies, that chromosome is trisomic. A familiar example is trisomy 21, which leads to Down syndrome. Polyploidy would mean having three or more complete sets of all chromosomes (not just one chromosome extra), so it’s a different situation. Nondisjunction is the error during cell division that can produce trisomy by failing to separate chromosome copies, but the resulting condition is described as trisomy. Genetic engineering, meanwhile, involves deliberate modification of genes and not simply an abnormal chromosome count.