chromosomes and genes humans

fig. 19.13 A map of Drosophila Chromosome..

Waldeyer is credited with the discovery of chromosomes in the year 1888 within the nucleus. He observed them as darkly stained bodies. However, it was the American William Sutton who noticed the similarities between the behaviour of the mendelian factors or genes and that of the..

>Culturing of human cells invitro, help in understanding the biochemical basis of inheritance. Human cytology and karyotyping helps in ascertaining the number, shape size and structural features of chromosomes. Study of monogygotic twins helps in distinguishing between..

Chromosome Mapping - It has been noted that in the dihybrid genetic crosses, a recombination frequency of less than 50% indicates linkage of the two genes involved. Morgan and Sturtevant found that the recombination frequency varies for different mutant gene pairs. The..

They are mutation involving change in number or structure of chromosomes. Change in number of chromosomes induced by mutagens can lead to aberrant gametes, which when fuse with normal gamete lead to aneuploid zygotes. Changes in chromosomal structure by mutation are b..

In bacteria, which being prokaryotic organisms, the entire hereditary material is packed into a single, irregularly folded compact mass called nucleoid or genophore or bacterial chromosome. It is short and simple consisting of a single DNA molecule. The DNA is in the form of a double heli..

. The core particle is formed by a group of proteins called histones. In a nucleosome there is an octomer of 8 histone molecules, two each of H2A, H2B, H3 and H4. In between the nucleosomes is the DNA portion not associated with histones and is called Linker DNA. A linker DNA with the nucleosome is..

, which are extremely larger than the normal ones are called giant chromosomes. They occur in some animal cells. Lampbrush chromosomes of amphibian oocytes and polytene chromosomes of Drosophile one common examples of giant chromosomes. Genome is the term use..

Morgan, along with Castle formulated the chromosome theory of linkage. It has the following postulates; 1. Genes are found arranged in a linear manner in the chromosomes. 2. Genes which exhibit linkage are located on the same chromosome. 3. Gen..

In the year 1902, Boveri and Sutton proposed the idea of chromosome theory of inheritance which was subsequently confirmed by Morgan in the year 1933. According to this theory, the Mendelian factors which are now called as genes, are located on the chromosomes and it i..