Chromosome

A chromosome is a DNA-containing structure that carries genes and associated sequences. Its DNA is packaged with proteins, and its organization and number vary across organisms and cell types.

DNA: A molecule that stores hereditary information through sequences of nucleotide bases. Chromosomes package DNA into structures that can be copied and distributed.
DNA replication: The cellular process that copies DNA before cell division. Replication produces the DNA copies that become sister chromatids.
Karyotype: An organized display of an individual's chromosomes, grouped by size, shape, and banding pattern. Karyotypes reveal chromosome number and large structural changes.
Bacterial chromosome: The main DNA molecule of a bacterium, usually a circular molecule located in the nucleoid. Bacterial chromosomes typically lack the multiple linear arrangement found in eukaryotic nuclei.
Gene: A DNA sequence that contributes to a functional product, such as an RNA molecule or protein. Genes are functional sequences arranged along chromosomes.
Sister chromatid: One of two nearly identical DNA copies formed when a chromosome replicates. Replicated chromosomes consist of sister chromatids until they separate.
Aneuploidy: A chromosome-number abnormality caused by the gain or loss of one or more chromosomes. Chromosome counts identify aneuploidies such as trisomy 21.
Eukaryotic chromosome: A DNA molecule packaged with proteins inside a eukaryotic cell’s nucleus or organelles. Eukaryotic chromosomes are usually linear and associated with histones.
Chromatin: The complex of DNA and proteins that makes up eukaryotic chromosomes. Chromatin is the material that organizes chromosome DNA in eukaryotic cells.
Mitosis: The process by which a eukaryotic cell separates duplicated chromosomes into two nuclei. Mitosis distributes chromosome copies to daughter cells.

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