Chromosome and Chromatid

Do you want to know the concepts of chromosome and chromatid its meaning, their discovery, number of chromosomes present in different organisms, the structure of chromosomes in different types of organisms, chromatid in various stages of a life cycle of a cell, formation of chromatid in the cell and the difference between the two concepts. If your answer is yes then this article is for you, it will provide you with all the necessary details and much more so do read the article till the end.

Difference between Chromosome and Chromatid

What is a chromosome?

The word chromosome comes from chroma, meaning “colour,” and soma meaning “body”. It was first there in the German language. A German scientist named Wilhelm von Waldeyer-Hartz, gave chromosomes their name because chromosomes easily accept dye and take on patterns of light and dark when exposed to different stains. Chromosomes are thread-like structures located inside the nucleus of animal and plant cells. Each chromosome is made of protein and a single molecule of deoxyribonucleic acid (DNA). The chromosomes carry hereditary information, which is responsible for the different characteristics present in every organism.  

How did the discovery of chromosomes happen?

During the 1880s, scientists worldwide were conducting countless experiments in cell biology. The German scientists Schleiden, Virchow and Bütschli were the first to discover and recognize the structure of what we today call chromosomes. During one such experiment, a scientist named Wilhelm Roux suggested that each chromosome carries a different genetic configuration; Theodor Boveri could test and confirm this hypothesis. Boveri’s major contribution was when he was able to prove that chromosomes are basic tools of heredity in organisms through his experiments.

Human chromosomes:

There are two types of chromosomes in humans: autosomes (body chromosomes) and allosomes (sex chromosomes). The allosome is responsible for carrying the sexual characteristics from one generation to another. Autosomes carry the other unique characteristics from one generation to another. Humans have 23 pairs of autosomes and a pair of autosomes, taking the total number of chromosomes to 46. Each chromosome contains highly condensed and coiled DNA consisting of millions of gene sequences. While some of the sequences are essential for life and code for essential proteins, some are “silent,” meaning they do not code for any proteins.

What Is a Chromatid?

A chromatid is one half of a replicated chromosome. Before cell division, chromosomes are copied and identical chromosome copies join together at their centromeres. Each strand of one of these chromosomes is a chromatid. Joined chromatids are known as sister chromatids.

Formation of a Chromatid:

A Chromatid is formed by chromatin which contains protein and DNA and is called a nucleosome when wrapped around these proteins in sequence. Before repletion, a chromosome is a single-stranded chromatid. After replication, a chromosome appears in an X-shape. After this, their sister chromatids are then separated during cell division to ensure that each daughter cell receives the appropriate number of chromosomes.

Chromatid in interphase:

Interphase is a phase that happens right before cell division. It is the phase where cells grow and it replicates the DNA and organelles to prepare for division. Chromatids play a very important role in the interphase. Following processes are involved in the interphase:

Prophase: Replicated chromatin fibres form chromosomes. Each replicated chromosome consists of two sister chromatids. Chromosome centromeres serve as an attachment for spindle fibres during cell division.

Metaphase: Chromatin becomes even more condensed and sister chromatids line up along the mid-region of the cell or the metaphase plate.

Anaphase: Sister chromatids are separated and pulled toward opposite ends of the cell by spindle fibres.

Telophase: Each separated chromatid is known as a daughter chromosome and each daughter chromosome is enveloped in its own nucleus. Two different but identical daughter cells are produced from these nuclei following the division of the cytoplasm, known as cytokinesis.

Sister Chromatid Exchange:

When two sister chromatids are in close contact with each other during cell division, the exchange of DNA material can occur. This process is known as sister-chromatid exchange or SCE. A low level of material exchange is typically considered safe. Still, when the exchange reaches excessive levels, it can be hazardous to the individual.

Difference between chromosome and chromatid:

• A chromosome is a thread-like structure present in the nucleus or nuclear region of the cytoplasm that is made up of a single molecule of DNA and proteins, carrying an organism’s genetic materials. However a chromatid is an identical half of a duplicated chromosome. After duplication of a chromosome, two identical halves are formed, each of which is called chromatids
• Chromosomes are more condensed than chromatids whereas, chromatids are less condensed than chromosomes
• A chromosome consists of a single, double-stranded DNA molecule. Chromatids are two molecules of double-stranded DNA joined together in the centre by a centromere
• Chromosomes have a thin ribbon-like structure whereas, chromatids have a thin and long fibrous structure
• Homologous chromosomes are not identical to each other and Homologous or Homozygous sister chromosomes are identical
• DNA in a chromosome is tightly packed but the DNA molecule is unwounded in chromatids and thus is free
• Chromosomes are capable of replication or duplication but chromatids cannot replicate or duplicate

Conclusion

In this article, we learned the meaning of chromosomes, its discovery, and details about the human chromosome. We also got to know the meaning of chromatids, their formation, and their role during interphase. Lastly, we got to know the difference between the two concepts.