Show the parallels between Mendelian laws and chromosomal theory of inheritance

Gregor Mendel, in 1865, performed experiments on pea plants and explained how traits are passed from one generation to the next. He gave three important principles which are now called Mendel's Laws: Law of Dominancethe, Law of Segregation and Law of Independent Assortment. He said that traits are controlled by specific factors, which we now call genes, but he did not know where these genes are located inside the cell.

In the early 1900s, Walter Sutton and Theodor Boveri gave the Chromosomal Theory of Inheritance, which explained that genes are present on chromosomes and chromosomes behave in a special way during meiosis. The movement of chromosomes during meiosis matches exactly with what Mendel had observed in his experiments. So, this theory gave a proper physical explanation to Mendel's laws and showed how inheritance works at the cellular level.

Although the Chromosomal Theory confirmed Mendel's principles, it also added new details. For example, the theory explains the physical mechanism of segregation and independent assortment by showing how chromosomes behave during meiosis. It also clarifies why linked genes (genes on the same chromosome) may not assort independently, which Mendel's laws did not explain.

Main Parallels Between Mendelian Laws and Chromosomal Theory of Inheritance

There are three main parallels that clearly show how Mendel's laws match with chromosome behavior.

1. Law of Dominance ↔ Allelic Interaction on Chromosomes

Mendel said that when two different alleles are present together, one is dominant and its effect is seen, while the other is recessive and hidden.

Chromosomal theory supports this by explaining that dominant and recessive alleles are present on homologous chromosomes and gene expression depends on how these alleles interact inside the cell.

Note: This interaction happens on the level of DNA and proteins, though that was understood in more detail later.

2. Law of Independent Assortment ↔ Independent Assortment of Chromosomes

Mendel observed that genes for different traits are passed independently of each other, if they are not linked.

Chromosomal theory explains that during metaphase I of meiosis, different pairs of chromosomes line up and separate independently. So, genes located on different chromosomes also assort independently. However, if two genes are located on the same chromosome, they may be linked and not assort independently — this was not known to Mendel.

Note: The Chromosomal Theory adds the explanation that if genes are close together on the same chromosome, they may be linked  and not assort independently. This was not known to Mendel.

3. Law of Segregation ↔ Separation of Homologous Chromosomes in Meiosis I

Mendel said that every individual has two alleles for each gene and during gamete formation, these alleles separate, so each gamete gets only one allele.

Chromosomal theory explains this by showing that during meiosis I, the two homologous chromosomes (each with one allele) separate and go into different gametes. So, the physical separation of chromosomes supports Mendel's Law of Segregation.

Note: The difference is that Mendel saw this as an abstract principle, while Chromosomal Theory showed the actual chromosomes moving apart.







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