Biology: Heredity

In the descendant of creatures, the hereditary symptoms are moved by chromosomes. These are made from nucleoproteins. The term chromosome was coined by Waldeyer. The small pieces of chromatin during the partition of cells are known as chromosome, on which genes are found.

DNA is responsible for storing and transferring genetic information while RNA directly codes for amino acids and acts as a messenger between DNA and ribosomes to make proteins. However studies showed that RNA replaces DNA in some viruses like Tobacco Mosaic virus, QB bacteriophage, etc. So, not every organism has DNA as their hereditary material, some have RNA. But, DNA is the predominant one and in the majority of higher level organisms, RNA plays the role of a messenger.

DNA is a double helix with the sugar-phosphate backbone on the outside of the molecule. The bases are on the inside, oriented such that hydrogen bonds are formed between purines and pyrimidines on opposite chains. The base pairing is very specific - A will always pair with T, G with C and the amount of adenine (A) is always equal to that of thymine (T) and the amount of guanine (G) to that of cytosine (C). Because of this specific base pairing, the two strands of a DNA molecule are complementary (each strand contains all the information required to specify the sequences of bases on the other). Complementary base pairing between DNA strands makes it uniquely suited to store and transmit genetic information from generation to generation. This complementary base pairing allows cells to copy information form one generation to another and even find and repair damage to the information stored in the sequences.

Sexual reproduction involves two parent cells; each parent gives some of its traits (characteristics) to the offspring. Sexual reproduction causes genetic variation because of blending of genes, chromosomal changes, shuffling of genes etc.

The chromosomal theory of inheritance is credited to papers by Walter Sutton in 1902 and 1903, as well as to independent work by Theodor Boveri during roughly the same period. It is a fundamental unifying theory of genetics which identifies chromosomes as the carriers of genetic material. It correctly explains the mechanism underlying the laws of Mendelian inheritance by identifying chromosomes with the paired factors (particles) required by Mendel's laws. It also states that chromosomes are linear structures with genes located at specific sites called loci along them. Although it was Mendel who had initially put forth the theory of genes affecting character, he was unable to gain any recognition for it. Then in 1900, three scientists, de Vries, Correns and von Tschermak independently discovered chromosomes existing inside the nucleus, thus proving Mendel's theory. This theory was then firmly established in 1902-1903 by Sutton and Boveri. They compared the behaviours of chromosomes to genes and deduced certain parallels, thus justifying Mendel's laws. In 1915, Thomas Hunt Morgan's work on inheritance and genetic linkage in the fruit fly Drosophila melanogaster provided incontrovertible evidence for this theory. Waldeyer has coined the term "chromosome" to describe basophilic stained filaments inside the cell nucleus. It is to be noted that JPSC said in revised answer key that all options are incorrect.

James Dewey Watson (born April 6, 1928) was an American molecular biologist, geneticist and zoologist, best known as one of the co-discoverers of the structure (double helix model) of DNA in 1953 with Francis Crick. Watson, Crick, and Maurice Wilkins were awarded the 1962 Nobel Prize in Physiology or Medicine for their discoveries concerning the "molecular structure of nucleic acids (DNA) and its significance for information transfer in living material".

James Dewey Watson (born April 6, 1928) was an American molecular biologist, geneticist and zoologist, best known as one of the co-discoverers of the structure (double helix model) of DNA in 1953 with Francis Crick. Watson, Crick, and Maurice Wilkins were awarded the 1962 Nobel Prize in Physiology or Medicine for their discoveries concerning the "molecular structure of nucleic acids (DNA) and its significance for information transfer in living material".