JMSS Science Practice Test

Approximately how many genes are contained in a nucleus?

5,000 20,000 50,000 100,000

Correct Answer:

20,000

Explanation:

Think of the nucleus as the library that holds our genome. In humans, there are about 20,000 distinct genes that code for proteins, plus additional genes for various RNAs. That makes roughly 20,000 genes contained in a nucleus when we talk about the number of different genes present. This is a standard, widely cited figure for the human genome. The other numbers are far from typical counts for human genes: 5,000 is too few, while 50,000 or 100,000 would be more than the human genome contains even when including noncoding RNA genes. If you consider that a diploid cell has two copies of each gene, you’d have two alleles for each gene, but the question usually refers to distinct genes rather than copies.

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