Self Assessment Answer # 1
for Lesson 4

by Dr Jamie Love Creative Commons Licence 2002 - 2005

  1. "n" is the one (normal) set of chromosomes. It is also the number of chromosomes in healthy gametes.
    Some people call "n" the "ploidy" of a species. While that is stretching into a slang usage, it is acceptable.

  2. Diploid is 2n - two (normal) sets of chromosomes. It is also the number of chromosomes in most cells that make up the body.

  3. Haploid is n (or 1n) - a single (normal) set of chromosomes. It is also the number of chromosomes in healthy gametes.
    Note : "n" is not 23, diploid is not 46 and haploid is not 23! Those are the values for a human cell but they are NOT the definitions. Those specific numbers are only examples (that I like to use because most folks are interested in how this all relates to humans).

  4. Aneuploid is any chromosomal set that is not of the "correct" count - but is not polyploid (see below). It has extra or missing chromosomes.
    These are often described as "2n - 1" or "2n +1", etc. but you get the idea.

  5. Polyploid is any condition with extra sets of chromosomes.
    These are often described as "3n", "4n", etc.

Final note - you may have noticed I dropped the "y" ending on aneuploidy and polyploidy. That was on purpose and to get you use to the idea that we use expressions like "Down syndrome is an aneuploidy because the extra chromosome causes an aneuploid condition."

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