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Q.
Monosomy and trisomy are respectively
Principles of Inheritance and Variation
Solution:
Monosomy refers to a condition in which a single chromosome is missing from the normal diploid set. It is represented as $2 n -1$. A trisomy has one extra chromosome and is represented as $2 n +1$. Trisomy $21 $ is an example of a trisomy in which cells have an extra chromosome number $21$ .