Structural Organization of Chromatin

What is a Chromosome?

Chromosomes are thread-like structures that are made of proteins and carry a strand of DNA. It is found in the nucleus of eukaryotic cells. During cell division, chromosomes replicate and separate. This ensures that each daughter cell receives a complete set of genetic material. Genes are located on the chromosomes in a particular sequence. The presence of different genes on the same chromosome is called Linkage. The sex chromosomes, X and Y, determine an individual’s biological sex: XX for females and XY for males in humans. Chromosomal aberrations occur when there is change in chromosome number or structure. It can lead to genetic disorders, such as Down syndrome or Turner syndrome....

Discovery of Chromosome

The chromosome was discovered in the late 19th century. German biologist Walther Flemming, in 1882, first observed thread-like structures during cell division in the cell nucleus, which he called “chromatin.” The term “chromosome” was first coined by W. Waldeyer in 1888. Waldeyer contributed significantly to understanding cell division and the visible thread-like structures he observed during mitosis. In 1842, Karl Nageli observed the rod-shaped chromosomes in the plant cell and termed them transitory cytoblast, which were later identified as chromosomes. The discoveries laid the foundation for understanding the role of chromosomes in genetics....

Structure of Chromosome

The chromosome structure consists of the following parts:...

Structural Organization of Chromatin

The chromosomes are present in the nucleus of the cell. The DNA along with the histone proteins forms a nucleosome and single nucleosome consists of eight histone proteins. These nucleosome are wrapped over DNA, to form a “beads on a string”-like structure. Multiple nucleosomes join together to form a chromatin fiber and Chromatin fibres together form a chromosome. To understand the difference between chromatin and chromosomes, please refer to the article ‘Difference Between Chromatin and Chromosomes‘....

Functions of Chromosome

The functions of chromosomes are as follows:...

Types of Chromosomes

Based on the position of the centromere, there are four types of chromosomes. These are as follows:...

Human Chromosomes

In humans, there are 23 pairs of chromosomes present, thus total 46. These 23 pairs of chromosomes can be divided into two types: autosomes and allosomes. The first 22 pairs are autosomes, and the last 23rd pair is the allosome, or sex chromosome. The sex chromosomes, X and Y, determine an individual’s biological sex: XX for females and XY for males in humans. Each chromosome contains highly condensed and coiled DNA consisting of millions of gene sequences. Chromosomal aberrations occur when there is change in number or structure of chromosomes which can lead to various genetic disorders, such as Down syndrome, Klinefelter syndrome, and Turner syndrome....

Karyotypes and Genetic Mapping

Karyotype represents the complete set of chromosomes of an individual, organized by size, shape, and banding pattern. It provides details about the chromosome count of an organism and how these chromosomes appear under a microscope. Karyotyping is a test to examine chromosomes in cells. It creates a photograph of chromosomes during mitosis or meiosis, providing a snapshot of cell division called a karyogram. It also provides information regarding the number, structure, length, and position of the chromosome. It is also used to identify abnormalities in chromosomes like Down syndrome, Klinefelter syndrome, Philadelphia chromosome, Trisomy 18, and Turner syndrome....

FAQs – Chromosomes and Their Function

What is a Chromosome?...