Chromosome

A chromosome is a threadlike structure made of protein and a single DNA molecule that carries genomic information. In plants and animals, chromosomes are located in the cell nucleus.

• Humans have 22 pairs of autosomes plus 1 pair of sex chromosomes (XX or XY) = 46 total chromosomes.
• Each chromosome pair includes one chromosome inherited from each parent.
• Chromosomes aren't visible in the nucleus when a cell is not dividing; they become more tightly packed during cell division and can then be seen under a microscope.

• If a stem says DNA in the nucleus is packaged into thread-like structures made of DNA coiled around histone proteins -> that's describing <u>chromosomes</u>.
• If a question asks for the typical chromosome count in a human cell -> <u>23 pairs (46 total)</u>, with 22 autosome pairs and 1 sex-chromosome pair.
• If a prompt contrasts "not visible when not dividing" vs "visible during division" -> it's pointing to <u>chromosome condensation during cell division</u>.