Explain Mendel's second experiment ? with diagram and mention it's ratio also.
Answers
After Mendel's first set of experiments, Mendel wanted to see if the inheritance of characteristics were dependent, or were they independent events. Mendel asked if the segregation of the heritable factors (allele) for one characteristic (gene) had any effect of the segregation of the factors for another characteristic. For example, did the segregation of the flower color factors have any effect on the segregation of the seed shape factors? So Mendel performed crosses in which he followed the segregation of two genes. Mendel crossed pea plants that differed in two characteristics, such as seed color and shape. A dihybrid cross is a cross in which the inheritance of two characteristics are tracked at the same time. The offspring of such a cross are called dihybrids.
Once again Mendel began with a true-breeding P generation, but this time true-breeding for two characteristics. For example, he crossed pea plants that had yellow and round seeds with a plant that had green and wrinkled seeds. From Mendel's first experiments, yellow seed color is dominant to green seed color, and round seed shape is dominant to wrinkled. So for the F1 generation, as before, the recessive traits disappeared, leaving Mendel with pea plants that had only round and yellow seeds. He then allowed the F1 generation to self-pollinate, and examined the resulting F2 generation. In the F2 generation, the recessive traits reappeared, as did two novel combinations of traits: round green seeds, and wrinkled yellow seeds. From these results, Mendel concluded that characteristics were inherited independently of each other. That is the only way that the two new combinations of traits could have developed. From these findings, Mendel developed his second law, the Law of Independent Assortment.
The given attachment refers to the chart represents Mendel's second set of experiments. It shows the outcome of a cross between plants that differ in seed color (yellow or green) and seed form. The letters R, r, Y, and y represent genes for the characteristics Mendel was studying. Mendel didn’t know about genes, however. Genes would not be discovered until several decades later. This experiment demonstrates that in the F2 generation, 9/16 were round yellow seeds, 3/16 were wrinkled yellow seeds, 3/16 were round green seeds, and 1/16 were wrinkled green seeds.
The Law of Independent Assortment, also known as or Mendel's Second Law, states that the inheritance of one trait will not affect the inheritance of another. Mendel concluded that different traits are inherited independently of each other, so that there is no relationship, for example, between seed color and seed shape. In modern terms, alleles of each gene separate independently during gamete formation.
You might think that Mendel's discoveries would have made a big impact on science as soon as he made them. But you would be wrong. Why? Because Mendel's work was largely ignored. Mendel was far ahead of his time and working from a remote monastery. He had no reputation among the scientific community and limited previously published work.
Mendel’s work, titled Experiments in Plant Hybridization, was published in 1866, and sent to prominent libraries in several countries, as well as 133 natural science associations. Von Nageli instead sent hawkweed seeds to Mendel, which he thought was a better plant for studying heredity. Unfortunately hawkweed reproduces asexually, resulting in genetically identical clones of the parent.
Charles Darwin published his landmark book on evolution in 1869, not long after Mendel had discovered his laws. Unfortunately, Darwin knew nothing of Mendel's discoveries and didn’t understand heredity. This made his arguments about evolution less convincing to many people. This is an example of the importance of the scientific inquiry mindset elimination of bias.
Even though he had repeated his studies using thousands of pea plants, and applied statistics to analyze his findings, Mendel's work was initially rejected as most biologists still believed in blending inheritance, and they did not understand his laws. It was not until after he died (January 6, 1884) that his work gained wide acceptance. By 1900, research into discontinuous inheritance - why do traits "disappear" in the F1 generation? - led to independent duplication of Mendel's work by Hugo de Vries and Carl Correns, and then the rediscovery of Mendel's writings and laws. Soon afterwards, other biologists started to establish genetics, the study of heredity, as a science.
