A chromatid is one of two identical halves of a replicated chromosome. During cell division, the chromosomes first replicate so that each daughter cell receives a complete set of chromosomes. Following DNA replication, the chromosome consists of two identical structures called sister chromatids, which are joined at the centromere.
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So what's a chromatid? Well, during DNA division, when a cell divides, it needs to take its DNA and duplicate it and then transfer half of it to one cell and half to the other cell. Well, DNA's arranged in chromosomes, as you know, so what happens is, as a chromosome replicates, or makes a copy of itself, it's arranged as two chromosomes next to each other, called chromatids. Then during mitosis, when the DNA is transferred to the two daughter cells, one of each of those chromatids is transferred to each of the two cells. So a chromatid is one copy of a chromosome after DNA replication.
William Pavan, Ph.D.
Senior Investigator, Genetic Disease Research Branch; Head, Mouse Embryology Section
Dr. Pavan's laboratory uses genomic tools to study how an embryo develops into a functioning organism. His group focuses on neural crest cells, a group of stem cells that differentiate into a variety of tissues throughout the body. In vertebrate development, neural crest cells form at the top of the neural tube. They then migrate throughout the body to populate the peripheral nervous system and form other tissues. When the genetic machinery that controls neural crest cell development goes awry, it can cause many human diseases, ranging from Waardenburg syndrome to cleft lip and palate.