When a cell is preparing to divide, it makes a new copy of all of its DNA, so that the cell now possesses two copies of each chromosome.
The two copies of the cell’s original chromosome are called “sister chromatids.”
During anaphase of cell division, the two chromatids will be pulled apart, and chromatid will be apportioned to the cytoplasm of each daughter cell.
A “chromosome” is defined as a large amount of DNA that is physically connected into a single structure.
For that reason, while the “sister chromatids” are attached to each other, they are considered to each be one half of a single chromosome.
Once they are separated during anaphase, each chromatid is considered to be a chromosome of its own, just like the original chromosome that they are copied from.
The term “chromatid” arose as a term to distinguish each copy of the parent chromosome during the period of time before the copies become independent chromosomes themselves.
Function of Chromatids
Chromatids allow cells to store two copies of their information in preparation for cell division.
This is vital to ensure that daughter cells are healthy and fully functional, carrying a full complement of the parent cells’ DNA.
Keeping the two copies of the cells’ DNA joined together makes it easier for the cell to ensure that one copy goes to each daughter cell.
When sister chromatids fail to separate during cell division, the consequences can be severe.
When sister chromosomes don’t separate properly during cell division, the result is that one daughter cell gets an extra copy of a chromosome, while the other lacks a copy completely.
Nondisjunction errors can lead to the deaths of daughter cells, which may lack essential genes to survive, or have gene balance problems due to having too many copies of the same gene to express.
Nondisjunction errors are even thought to play a role in cancer. Though different types of cancers have different causes, nondisjunction errors are thought to be one of many ways that a cell’s “programming” can become disrupted, leading it to run amok as a cancer cell.