Chromosomal theory of inheritance

 After the discovery of Mendel’s laws of inheritance, scientists turned naturally to the physical basis of heredity. Sutton demonstrated the similarities between the meiotic behavior of paired chromosomes and the behavior of pairs of Mendelian factors. He could explain Mendel’s principle of segregation on a cytological basis. The chromosomal theory of inheritance was proposed independently by Sutton and Boveri in 1902. This theory states that individual genes are found at specific locations on particular chromosomes and that the behavior of chromosomes during meiosis can explain why genes are inherited according to Mendel’s laws.

Observations that support the chromosome theory of inheritance include Sutton and Boveri’s arguments for their chromosome theory of heredity were essential as follows:

• Since the sperm and egg cells provide the only bridge from one generation to other, all hereditary characters must be carried in them.

• The sperm cell lose practically all their cytoplasm in the process of maturation, as can be seen by observation under the microscope. Since the sperm contributes as much to heredity as does the egg, the hereditary factors must be carried in the nucleus.

• The union of sperm and egg each with its single set of chromosomes re-establishes for the new organism with two sets of chromosomes like previously seen in the body cells of the parent organism.

• During cell division, chromosomes divide accurately. This gives the idea that genes are carried on chromosomes.

Comments

Post a Comment

Popular posts from this blog

Morgan’s experiment: proof of chromosomal theory of inheritance

Image
 Morgan worked on the eye color of Drosophila. He observed that the pattern of transmission of the white eye gene was identical to that of the X chromosome of Drosophila. This prompted Morgan postulate that the gene for eye color is located on the X chromosome. This was the first demonstration of an association between a specific gene and a specific chromosome. His work gave direct evidence in support of the chromosomal theory of inheritance. The white-eyed male fly was crossed with the red-eyed female, all the F1 offsprings were red-eyed. This gives an indication that the white eye is controlled by a recessive allele. The predictions match the F1 phenotypes, but this set of phenotypes could also be explained by a gene that is not on the X chromosome since all the flies were red-eyed (regardless of sex). So, the real test comes when the F1 is mated to make the F2 generation. Something strange happened in F2: all of the female F2 flies were red-eyed, while about half of the male F2 ...
Read more

Chromosome number

Image
Chromosome number in every species is generally constant. In higher organisms, the number of chromosomes in a somatic cell is called somatic number irrespective of the ploidy level (number of basic chromosome set) and is represented by 2n. In the gametes, the chromosome number is reduced to half, it is known as the gametic number or haploid number and is represented by “n”. Some organisms including many plants have three or more sets of chromosomes and are referred to as polyploid. The basic chromosome number is denoted by “x” so that the chromosome number of a diploid cell or individual is expressed as “2x”. Diploid: 2n = 2x, n = x Tetraploid: 2n = 4x, n = 2x Hexaploid: 2n = 6x, n = 3x
Read more

Prokaryotic nucleoid

Image
 Recent work by a number of workers demonstrated that the network of threads consists of a single chromosome in the form of a ring. The exact three-dimensional arrangement by which 1100μ -1400μ long DNA chain, which forms 80% of the chromosome by mass (the remaining 20% being protein + RNA), is packed in an lμ long nucleoid, which could also be established now. At least two proteins, which bind DNA, resemble histones of eukaryotes and organize the DNA into structures comparable to nucleosomes of eukaryotes. It has been shown that the chromosome of E. coli is organized in about 45 loops, which radiate out from a dense proteinaceous scaffold, which is assumed to anchor the DNA. In each of the 45 loops, DNA is supercoiled and complexed with protein. The functional significance of looped domains is not clear but they do not represent units of transcription as in the case of lampbrush chromosomes.
Read more