Chromosomal Theory of Inheritance

Introduction

• In the early 1900s, Boveri and Sutton were credited for The chromosomal theory of inheritance. It is all about genetics fundamentals
• They said genes are the unity of the heredity present in the chromosome. Chromosomes are known to bear genetic materials
• After the discovery of Mendel Deliannetics, the Chromosomal theory of inheritance came into existence
• Society didn’t accept the Mendelian experiment. They didn’t accept the concept of genes and the drastic changes in Scientific ideas. People didn’t support his idea of the concept of evolution
• Due to a lack of communication, he is unable to convey to the people, and Mendel’s approach to the biological rules has become inappropriate
• As time passed, many scientists such as Vries, Correns, and Tschermak found the chromosome inside the nucleus
• Sutton and Boveri observe chromosome behaviour during behaviour vision
• They observed with the help of a telescope and also proved the Mendel law with the aid of chromosomal motions
• During Anaphase, they show chromosome segregation
• The idea of the Chromosomal theory of inheritance came from the idea of chromosomal segregation and by the Mendelians principles
• Later T.H Morgan demonstrate the linkage and recombination with the help of fruit flies (Drosophila melanogaster)

Explanation of Chromosomal Theory of Inheritance

Chromosomal Theory: Linkage and Genetic Recombination

• Inheritance of the gene is described by linkage and recombination
• For more than two generations, the same gene of the same combination is inherited together in case of linkage
• In recombination, offspring are produced by the exchange of genetic materials
• However, Mendelian genetics came up with the theory of chromosomal inheritance, which was rejected due to a lack of proof and technology. But later, many scientists proved Mendel’s results
• T.H.Morgan proved chromosomal inheritance which became the platform for the development of the concept of linkage and recombination
• In the case of linkage, the DNA remains in the same chromosome for more than two generations
• In recombination during the time of meiosis, the genetic material gets transferred during crossing over and leads to the formation of offspring

Morgan’s Experiment

In 1910 Thoams Hunt Morgan used fruit flies(Drosophila melanogaster) to explain the variation in offspring is caused by sexual reproduction. He experimented with fruit flies and observed more than 1000 fruit flies with red eyes but only one male fly with white eyes.

The same chromosome determines both eye colour and sex. Some genes are carried from parents to the offspring through chromosomes.

He even published an article in the name of “Sex limited Inheritance in drosophila”.

He chose fruit flies due to the reasons mentioned below.

• One can easily differentiate both the male and female drosophila
• One single mating is capable of producing many offspring
• It can easily cultivate in the synthetic medium in the laboratory
• It has a shorter lifespan of about 2 weeks.
• Different types of hereditary variations are available.

In his experiment, he found out white colour is only colourable in males due to the reason the white colour trait is discoloured in the X chromosome. As females have only one X chromosome, they won’t show a white eye. It has proven the inheritance of parental traits differs for each sex.

He conducts a hybrid cross with males (red eye and brown body) and females (white eye and yellow body). When he conducts self-crossing in F1, he didn’t get the ratio of 9:3:3:1 in the F2 generation.

Where – is female alleles and – is male alleles

BBEE is 9

Bbee is 3

bbEe is 3

bbee is 1

Based on the presence or absence of non-parental combination, it is divided into two types

1. complete linkage and 
2. incomplete linkage

There are four types of recombination they are

1. Homologous Recombination
2. Non-homologous Recombination
3. Site-Specific Recombination
4. Mitotic Recombination

Chromosomal Basis of Inheritance

Boveri and Sutton Chromosomal’s theory of inheritance supports Mendel’s laws. Here are some of the observations made by Boveri and Sutton in this theory

1. The pairs of Homologous chromosomes move as the discrete structure during the process of cell division meiosis. This homologous chromosome is independent of other pairs of chromosomes.
2. There is the random distribution of chromosomes into the pre gametes. It is from each homologous pair.
3. Each parent synthesises gametes. It contains just half of its chromosomal complements.
4. The size and shape of male gametes(sperm) and female gametes(egg) varies. But both egg and sperm have the same number of chromosomes. It indicates a similar genetic contribution for each parent.
5. During fertilisation, chromosomes present in the gametes combine to produce offspring with the same number of chromosomes as their parents.

The Role of Chromosomes in Inheritance

• When Mendels proposed the law of inheritance, he didn’t know what the cal properties of his “particles” where
• In 1882 August Weismann suggested the location of hereditary materials as chromosomes
• In chromosomes, genes are located
• The chromosomal theory of inheritance explains the idea of the location of the genes
• The composition of chromosomes is a single pair of DNA and many proteins
• Locus is the term given to the physical location of a gene in the chromosome
• As chromosomes carry genes hence during cell division, one pair of chromosomes from mother and other father combines to form offspring. The hereditary materials from the parents are carried to offspring with the help of chromosomes

Points to Remember

• The explanation of the chromosomal theory of inheritance states that genes are located in the specific location of the chromosomes
• T.H. Morgan gave a strong confirmation of the chromosome theory. He experimented with the help of fruit flies(Drosophila)
• Morgan discovered a mutation. He noted that male and female flies have separate mutations as the male flies have a white eye, and the female fly has a red-eye
• From the eye colour change, the colour gene is colourant in the X chromosome

Conclusion

In the article on the chromosomal theory of inheritance, we have read about the chromosomal basis of inheritance, the observation made during the chromosomal inheritance, Morgan’s experiment, and the importance of chromosomes in the inheritance.