Introduction
Chromosomes are a thread-like structure made up of nucleic acids and proteins found within the nucleus of live cells. They are primarily responsible for conveying genetic information in the form of genes.
In the early 1900s, Boveri and Sutton postulated the chromosomal hypothesis of heredity. In genetics, it is the most fundamental idea. According to this idea, genes are the units of heredity, and they are found in chromosomes.
The Chromosomal Theory of Inheritance
Long after Mendelian genetics, the Chromosomal Theory of Inheritance was developed. Society did not accept such radical changes in scientific concepts during Mendel’s experimentation. They couldn’t understand the existence of distinct variables like genes that would segregate without mixing because it contradicted their theory of evolution due to continual changes. Furthermore, the means of communication at the time were inadequate, preventing information from reaching the public.
Mendel’s mathematical approach to proving natural laws was also unacceptably ineffective. Scientists Vries, Correns, and Tschermak identified chromosomes inside the nucleus as time went on. When the cells were divided, Sutton and Boveri watched the behaviour of the chromosomes. This process grew easier with the developments in microscopy technology. As a result, they used chromosomal movement to show Mendel’s laws.
They demonstrated chromosomal segregation during cell division’s Anaphase phase. The chromosomal theory of inheritance was born from the idea of chromosomal segregation mixed with Mendelian principles. T.H. Morgan advanced and proved the work by using Drosophila melanogaster to demonstrate how sexual reproduction caused differences.
Chromosomal theory: Linkage and Genetic Recombination
Morgan noticed that two genes did not segregate when a pair of features was crossed according to Mendel’s law. When two genes were found on the same chromosome, the likelihood of a parental combination in the next generation was substantially higher than that of a non-parental combination. Linkage refers to the physical relationship of genes.
The non-parental gene combinations in a dihybrid cross were referred to as genetic recombination. Following the discovery of linked genes, the frequency of corresponding genes influenced the manifestation of phenotypes in subsequent generations.
Sturtevant, a student of Morgan’s, discovered the location of corresponding genes on a chromosome by measuring their frequency of genetic recombination using the gene mapping procedure. During the Human Genome Project, constructing a connection map was widely used.
Findings of Chromosome Theory of Inheritance
The Chromosomal Theory of Inheritance supports Mendel’s rules. The following are the findings of this theory:
- During cell division (meiosis), homologous chromosome pairs move as discrete structures separate from other pairs of chromosomes.
- Each parent produces gametes, which make up half of their chromosome complement.
- Female (egg) and male (sperm) gametes have the same number of chromosomes, ensuring equal genetic contributions from both parents.
- During fertilisation, the gametic chromosomes combine to produce offspring with the same number of chromosomes as their parents.
The Chromosome Theory of Inheritance supports Mendel’s law.
The chromosome or gene appears in pairs in somatic cells because one chromosome comes from the father and the other from the mother, forming a homologous pair.
Homologous chromosome pairs segregate autonomously of additional chromosome pairs during meiosis or gametogenesis. As a result, a gamete only has one type of chromosome, each containing one of two alleles for a particular trait.
The random distribution of chromosomes from each homologous pair into pre-gametes appears analogous to Mendel’s law of independent assortment.
Chromosomes are also passed down from generation to generation. In addition, the number of chromosomes in each organism is fixed.
Despite their differences in size and shape, male and female gametes have the same number of chromosomes, implying equal genetic contributions from both parents.
During fertilisation, the gametes join to produce offspring with identical chromosomes as their parents.
T.H Morgan worked on fruit flies and gave certain observations .
- According to him, male and female flies inherited mutations in distinct ways that changed the colour of their eyes.
- Eye colour genes were present on the X chromosome because of the inheritance pattern.
Conclusion
You’ve clearly understood the chromosome theory of inheritance, Mendel’s rules of Chromosomal Theory of Inheritance classification. Homologous chromosome pairs segregate autonomously of additional chromosome pairs during meiosis or gametogenesis. As a result, a gamete only has one type of chromosome, each containing one of two alleles for a particular trait.