What is the relationship between chromaids and chromosomes?

Answer 1

Normally a cells chromosomes are single strands - a bit like a pice of string. Just prior to cell division, a chromosome replicates (=makes another copy of itself) and these two copies are joined together at a point called the centromere. Each copy is now called a chromatid and being joined at the centromere make the familiar "X" shape, with each copy (chromatid) forming a side of the X and will have exactly the same sequence of genes down its length as the other chromatid (they are copies!). In cell division the copies (chromatids) will be pulled apart (X becomes > <) to become chromosomes in their own right.