Chromosomes and chromatids are confusing terms unless you know the process of cell division. We give you a brief description differentiating the two terms with their definitions, relationship and functions.
Did you know?
There are 46 chromosomes in our body, and hence 92 chromatids, just the double of chromosomes.
Genetics is the study of genes which are units of a cell that decide what features a living organism will inherit from its parents. If a child inherits his father’s looks or features like hair, eyes, it’s because of the genes. Hereditary diseases are also carried from parent to child and from generation to generation, because of genes. Genes are made of long strands of DNA (Deoxyribonucleic acid) molecules which are found in chromosomes and chromatids. But what are these? Chromosomes and chromatids are thread-shaped structures in the nucleus of eukaryotic cells (cells consisting of a nucleus within a membrane). They consist of extremely long strands of DNA material which are carriers of genes and regulatory elements. Let us have a closer look at what is what.
What are chromosomes?
The word chromosome is derived from the Greek language, chroma meaning color, and soma meaning body. Since chromosomes and chromatin are very brightly colored, hence the name. Chromosomes when inside a nucleus that is not undergoing cell-division is not even visible under a microscope. Each chromosome consists of a tightly-coiled DNA around the proteins.
An Indonesian cytogeneticist, Joe Hin Tjio first discovered in 1956 that there are 46 chromosomes in every human body. Chromosomes are packaged chromatin, a complex of macro-molecules found in cells, which consists of DNA, proteins, and RNA.
What are chromatids and how are they related to chromosomes?
During cell division, when chromosomes replicate themselves so as to give each daughter cell a complete set of chromosomes, each replication that is joined by a centromere is called a chromatid.
When replication takes place, only the number of DNA is increased but not that of chromosomes. In short, the same chromosome contains two DNA double strand molecules. Replication also known as duplication of chromosomes, forms identical strands of chromatids which later separate during cell division to form individual chromosomes. So, since there are 46 chromosomes in the human body, the number of chromatids is just the double of it – 92. Each chromosome therefore consists of two chromatids.
Check the illustration of cell division and mitosis given above. Here as you can see, individual chromosomes replicate themselves and form pairs of chromatids. When these chromatids undergo mitosis, they separate further producing individual, identical chromosomes.
Thus, this process continues to produce chromatids and chromosomes. At the end of mitosis, the number of chromosomes are similar to that of the parent cells.
Sister chromatids
Sister chromatids are those that emerge out of the same chromosome, and are joined together by a centromere. During mitosis, when chromatids separate from each other, those strands are called daughter chromosomes.
With this simple understanding of cell-division, the two terms chromosomes and chromatids become very easy to differentiate, understand and relate. Chromatids are thus essential components of a duplicated chromosome.