Chromosome

Long thread-like structures that are found in the nucleus of a cell.

Chromosomes carry genes, which are hereditary materials.

They consist of substances called DNA and proteins called histones.

Each chromosome is made up of two parallel strands called chromatids. Each pair of chromatids is connected at one point by a structure called centromere.

Chromosomes occur in pairs in body (somatic) cells. Each pair of the chromosomes has a characteristic length.

The member of each pair is called a homologous chromosome.

During sexual reproduction, each parent contributes one of the chromosomes of a homologous pair.

Along the length of the chromosome is a series of structures called genes.

It is genes that determine the characteristics of the cell and its progeny.

There are definite constant number of chromosomes in each cell for every species of animal or plant; e.g. in humans each somatic cell contains 46 chromosomes, while each gamete contains 23 chromosomes. On fertilization, the number 46 (diploid number) is restored in the zygote.