What are Chromosomes?
Where do genes find themselves in a cell? Odds are, you have heard the punchline before: genes lie on chromosomes. You may have even heard the second punchline, the one that is ushered in the modern genetic age: genes are DNA stretches specifying proteins.
Chromosomes are a thread-like structure of nucleic acids and proteins located within the nucleus of living cells and are primarily involved in gene-shaped genetic information. The Swiss botanist Carl Wilhelm von Nageli discovered chromosomes and was the first person to research the cell divisions.
The Chromosomal Theory of Inheritance
It is the fundamental genetic theory that recognizes chromosomes as the bearers of genetic material. Theodor Boveri and Walter Sutton are the two scientists who have been credited with developing the Inheritance Chromosomal Theory. In the early 1900s, Boveri and Sutton gave the chromosomal theory of inheritance. It is the fundamental genetic theory. According to this theory, genes are heredity units, and they are found in the chromosomes. Inheritance chromosomal theory came into being long after Mendelian genetics. Society wasn't acceptable to such drastic changes in their scientific ideas during Mendel's experimentation. They did not believe there were such distinct variables as genes that would Separate without combining, as this did not help their notion of continuous evolutionary shifts.
In addition, the means of communication at that time were weak, as a result of which the information could not be transmitted to the masses. Mendel's scientific approach to proving biological rules has always been inappropriate. Scientists Vries, Correns, and Tschermak found chromosomes that remained within the nucleus as time passed. Sutton and Boveri discovered when the cells were divided they observed the behaviour of the chromosomes. This task became simpler with the advances in the microscope. Thus, they proved the laws of Mendel with the aid of chromosomal motion. They showed chromosome segregation during the cell division Anaphase. The idea of chromosomal segregation combined with the Mendelian principles has given rise to Inheritance's Chromosomal Theory. The research was carried out further and was proved by T.H. Morgan, who used Drosophila melanogaster to demonstrate how it induced differences in sexual reproduction.
Chromosomal Theory - Linkage and Genetic Recombination
Morgan found that two genes did not segregate as per Mendel's law when crossing a range of characteristics. If two genes were present on the same chromosome, the probability of obtaining a parental combination in the next generation was much higher compared with the non-parental combination. This physical gene association was termed a connection. In a dihybrid cross, the word genetic recombination identifies the combinations of non-parental genes. Once connected genes were discovered, the frequency of connected genes also influenced trait appearance in the next generation. A Morgan’s student, Sturtevant, discovered the location of the related genes on a chromosome by measuring their genetic recombination frequency using the gene mapping technique. This method of producing a map of ties was commonly used during the Human Genome Project.
Observations of Chromosomal Theory of Inheritance
The inheritance chromosomal theory supports Mendel's laws. The observations of this theory are listed below:
The pairs of homologous chromosomes migrate as discrete structures independent of other chromosome pairs during the process of cell division-meiosis.;
Chromosomes of each homologous pair are randomly distributed into pre-gametes.
Gametes are synthesized by each parent and contain just half of their chromosomal complement.
While the size and shape of the male and female gametes (sperm and egg) vary, they have the same number of chromosomes, indicating similar genetic contributions for each parent.
During fertilization, gametic chromosomes combine to produce offspring with the same number of chromosomes as their parents.
Key Points
Boveri and Sutton's inheritance chromosome theory states that genes are found at specific chromosome locations, and that chromosome behaviour during meiosis may explain Mendel's inheritance laws. Thomas Hunt Morgan, who studied fruit flies, provided the first strong confirmation of the chromosome theory.
Morgan discovered a mutation affecting the colour of the fly-eye. He noted male and female flies inherited the mutation differently.
Following the pattern of inheritance, Morgan assumed that the eye colour gene must be located on the X chromosome.
What is Mutation?
The mutation is defined as the change or the permanent alteration of the nucleotide sequence of the genome of an organism. Our DNA can undergo changes in its basic sequences A, C, G and T. This results in changes in proteins that are DNA-synthesized. Generally, the cells can identify and restore any damage that could be done by mutation until it is permanent.
The Causes of Mutation
The mutation results in genetic differences between the species. Few mutations with positive effects are transferred to successive generations. For example, sickle cell anaemia is the result of a mutation in the gene that codes for the synthesis of the protein haemoglobin. The red blood cells take the form of a sickle. Within the African population, however, this mutation also protects against malaria.
Cancer is the most common mutation-related disease in a number of growth-control cells.
FAQs on Chromosomal Theory of Inheritance
1. What do you mean by Chromosome?
Chromosome looks like a thread and is made of protein, coiled material. Chromosomes are found in the nucleus of all cells, storing the essential genetic material DNA that passes from generation to generation. Structure: There are generally 8 parts of a chromosome; centromere or primary constriction or kinetochore, chromatids, chromatin, secondary constriction, telomer, chromonema, and matrix.
2. What are the observations that support the Chromosome theory of inheritance?
Remarks supporting chromosome inheritance theory include-
Like Mendel 's genes, chromosomes come into matched (homologous) pairs in an organism. One member of the pair comes from the mother and one from the father for both genes and chromosomes.
Homologous pair members separate in meiosis so that every sperm or egg receives only one member. In Mendel 's segregation law, this process mirrors the segregation of alleles into gametes.
In meiosis, the members of different chromosome pairs are sorted into gametes independently of each other, just like the alleles of different genes in Mendel 's self-assortment law.
3. Why are chromosomes important?
Chromosomes are a crucial part of all living beings as it carries the basic genetic or hereditary material called genes which provides the genetic information to many cells. Cellular functions are important for the survival and proper functioning of all living organisms. In addition, the chemical composition of the chromosomes is covered by histones and proteins that play a major role in metabolism and also provide protection from chemical enzymes. This helps the DNA to function without any hindrance during cell division. Furthermore, non-histone proteins that are present in chromosomes regulate gene action.
4. What were the observations made by the scientist in the chromosomal theory of inheritance?
The chromosomal theory of inheritance had many observations that were stated by the scientists. They are given as below:
During meiosis cell division, the pairs of the homologous chromosome move together and are independent of the other pairs of chromosomes present in the cell.
The pre-gametes have a random distribution of chromosomes which are from each pair of the homologous chromosome.
The gametes synthesized by the parents are composed of only half of their chromosome components.
The female and male gametes have the same number of chromosomes although they are different in size and shape which leads to equal distributions of chromosomes from each parent.
5. What are linkage and recombination?
Linkage is the process where two or more genes become linked and are inherited together for more than two generations. On the other hand, recombination means the genetic material between two different parents is exchanged leading to the production of offspring that can have a combination of traits. Thus, there is an exchange of genetic material that occurs in recombination. The chromosomal theory of inheritance showed such observations and the experiment performed by T.H. Morgan on fruit flies also led to the concept of linkage and recombination of genes.
6. Do chromosomes have any role in cell division?
Chromosomes contain deoxyribonucleic acid or DNA, which is considered as the main component for carrying forward important processes like replication, transcription and protein synthesis. Without DNA, the whole bodily processes that occur in the living organisms’ bodies may be disrupted. For cell division to occur, the chromosomes first replicate and undergo cell division which is either through the process of mitosis or meiosis. The chromosomes need to replicate properly so that there is a proper amount of DNA in the cell after division. Mutations in chromosomes can lead to many disorders.
7. Is there any evidence that supports the chromosomal theory of inheritance?
Yes, evidence that supported the chromosomal theory of inheritance was the contributions made by various scientists for it.
Mendel’s ‘factors’ (now genes) came in matched or homologous pairs in a living organism. The genes and chromosomes pair came from each parent and had the characteristic of both.
The members of the homologous pair of the chromosome separate during meiosis cell division which is similar to the law of segregation as stated by Mendel.
Different chromosome pairs are arranged in gametes independently in meiosis which can be supported by Mendel’s law of independent assortment.
