Chromosomes and Genes

The genes in your body contain instructions for producing one specific molecule, usually a protein. These proteins are responsible for controlling how our bodies develop and function; they also determine many of our physical characteristics like eye colour, blood type, and height. Each human body cell contains one set of 23 chromosomes inherited from our mother and one set of 23 chromosomes inherited from our father. Humans have 46 chromosomes in their somatic (non-reproductive) cells, and each of us has inherited one set of 23 chromosomes from each parent.

Deoxyribonucleic acid (DNA) combines together to form Genes. Protein is synthesised based on the blueprint presented by the DNA containing the code. The sizes of the proteins for which they code for determines the gene’s shape and size. Each DNA molecule has a spiral staircase-like double helical structure that resembles millions of steps. These staircase-like steps consist of four types of molecules called nucleotides bases. It is in each step that the base adenine (A) pairs with the base thymine (T), or the base guanine (G) pairs with the base cytosine (C). 

X and Y chromosomes are found in the nucleus of the cell and are organised as packs of DNA in the nucleus. DNA is represented inside the chromosome.  Each species has a unique set of chromosomes with respect to number and organisation. Chromosomes possess many intricate elements that facilitate processes such as replication and segregation. Humans have 23 pairs of chromosomes–22 pairs of numbered chromosomes and one pair of sex chromosomes, autosomes, which is derived from each parent, so each child gets half a chromosome each from the mother and half from the father.

History

Darwin identified a microscopic unit of inheritance and named it Gemmule to describe, This came to be known as Chromosomes. Chromosomes were first observed during cell division by Wilhelm Hofmeister in the year 1848. In that year he speculated that chromosomes are the carriers of inheritance. The word “gene” was coined by Danish botanist Wilhelm Johannsen in 1909 to describe these fundamental physical and functional important units of heredity. Since the dawn of civilization, mankind has considered the influence of heredity and applied its principles to the improvement of cultivated crops.

The laws of Mendelian inheritance were developed after Mendel conducted a large number of experiments with pea plants in an attempt to show that characteristic traits passed from parent to offspring follow a specific pattern. It was Ernst Haeckel who first described in the year 1866 the nucleus as a centre for the transmission of elemental characteristics determining one’s ancestry. 

Two important characteristics of chromosomes are mentioned by Theodor Boveri that are located within the nucleus. First was that each and every chromosome is unique. The other was that  information was passed from one generation to the next by  the chromosomes. 

Location and Structure

This is a major difference between the structure and location of chromosomes in viruses, prokaryotes and eukaryotes. The nonliving viruses have chromosomes consisting of either DNA or RNA , they are tightly packed into each other in the viral head. The eukaryotic chromosomes are enclosed by a nuclear membrane unlike the prokaryotic one’s. Eukaryotic cell chromosomes consist primarily of DNA attached to the protein core. 

In most cases, genes are formed from deoxyribonucleic acid (DNA). Molecular DNA consists of two nucleotide chains that form a ladder-like structure around each other. Sugars and phosphates line the sides of the ladder, and nitrogenous bases bind the rungs. These bases are named Adenine (A), Guanine (G), cytosine (C), thymine (T). An Adenine base pairs with Thymine with the help of one hydrogen bond (thus forming an A–T ladder rung); similarly, a Cytosine base binds with Guanine base by three hydrogen bonds with one another. 

The chains unwind when the bases of the two chains are broken, and nucleotides within the cell attach itself to the exposed base part of the chains. The free nucleotides in the cell line up on both chains according to the base-pairing formula, where A is paired with T, and C is paired with G.

Conclusion

DNA secondary structure’s importance to many aspects of cellular life is invaluable. The replication, transcription, and regulation of gene expression of many genes are entirely dependent on variations in DNA structure’s local structure. It is possible to form an unusual structure called the Holliday structure through the process of recombination that leads to rearrangements of genes.