Genetics Pop Quiz #3: How many chromosomes do humans have?
Question: How many chromosomes do humans have? (One person, not all of humanity.)
a. 10
b. 23
c. 46
d. 2200
e. 25,000
Answer: c. 46 chromosomes or 23 pairs.
Of the 46 chromosomes, two are sex chromosomes – XX in women and XY in men. All somatic cells have the full complement of 46 chromosomes except for germ cells (sperm and eggs) which have 23 chromosomes. We get one set of 23 chromosomes each from our mother and father. When a sperm and egg fuse at fertilization, the resulting embryo has the full set of 46 chromosomes (barring any abberations).
A chromosome (in Greek chroma = colour and soma = body) is, minimally, a very long, continuous piece of DNA, which contains many genes, regulatory elements and other intervening nucleotide sequences.
The Human Genome Project also has a Human Chromosome Launch Pad that has link lists for each of the chromosomes with links to “gene maps, sequences, associated genetic disorders, nonhuman genetic models, identified genes, research efforts and laboratories, and other information.”
NB: e is a trick answer because we have an estimated 20,000-25,000 genes.
It’s also tricky if you are into life cycle evolution, because both b and c are correct answers. Unless you’re discriminating against those poor haploid gametes, that is.
Thanks for the comment, PZ. I feel honored you dropped by.
You’ve reminded me how far I’ve gotten from basic bio by mentioning life cycle evolution. I realize that I have the tendency to oversimply things, but I swear I wasn’t intentionally trying to discriminate against haploid gametes. I mentioned them but they’re of the minority.