WHAT IS A CHROMOSOME?

Before knowing what a chromosome is, we first need to know chromatin.

CHROMATIN,

DNA and histone protein together make the chromatin, or we can say DNA wrapped around protein makes chromatin. As the eukaryotes, DNA is really long, so to fit inside that of nucleus it needs to be shortened or condensed. Histone protein is also known as histone octamer as it has 8 subunits, its like the beads on the string kind of structure. AND in prokaryotic cells(bacterial cells) the DNA is circular and tightly packed so they do not get scattered inside the cell even if they don't have a well defined nucleus.

CHROMATIN STRUCTURE

Now during cell division after the DNA is replicated in the S phase of interphase, the chromatin material starts to condense more. The process of scaffolding helps DNA to be properly anchored with each other for very condensed and thick structures.The highly condensed DNA present in plants animals and all living beings which transfers the hereditary material from one generation to the next through genes is known as chromosomes. They can be easily stained and  seen under the light microscope during the cell division in the metaphase Chromosomes are the house of genes And the genes are turned into protein through translation which are used by the body. The center of the chromosomes are known as centromere.

STRUCTURE OF A CHROMOSOME

After seeing the picture given above one must be thinking why 2 chromatids are present?

 So, what is a chromatid?

Basically chromatids are the sister pair of chromosomes.

These chromatids are called sister chromatids but during zygote formation the haploid cells combine and become diploid and then the chromatids combined are not sister chromatids.

Sister chromatids gets separated in the anaphase. 

Every organisms present on this earth has a different chromosome number:

chromosomes are counted in pairs as one comes from paternal side and one from maternal side.

• HUMANS : 23 pairs or 46 chromosomes
• HORSES : 32 pairs or 64 chromosomes
• DROSOPHILLA : 2 pairs or 4 chromosomes
• MAIZE : 10 pairs or 20 chromosomes.

Chromosomes have three parts: 

• p arm (above arm)
• q arm (below arm)
• centomere - This determines the shape and structure of chromosomes.