Emergence of Evolutionary Thoughts and Mendelism’s Contribution to Genetics

Mendelism

Introduction:

Evolution refers to the continuous and gradual process of change that occurs over a period of time. During evolution, characteristics of living organisms undergo changes and leads to the formation of new species. Scientists have predicted that the Earth is around 4.6 billion years old. Around 3 billion years ago, the first life on earth appeared. It was a unicellular tiny prokaryote.

Around 2 billion years ago, these tiny prokaryotic cells evolved into larger cells that contain a nucleus. Later on, smaller prokaryotic cells resided in larger cells and got transformed into organelles over the course of evolution (Example: Mitochondria). Around one billion years ago, multicellular organisms evolved. It is also anticipated that various animals and plants have been evolving for the past 500 million years.

History of Evolutionary Thoughts:

It is anticipated that the emergence of thoughts about the process of evolution of species began during the fourth century BC. Several theories of evolution have been proposed by various scientists. Most importantly, Greek philosophers, Plato and Aristotle provided their views on the evolution of species on earth.

They believed that each organism on earth has been created in its present form, and they remain unchanged. Various evolutionary theories have been proposed by different scientists at different time periods.

French biologist Jean Baptiste Lamarck (1744-1829) has proposed that living things could transfer the acquired traits to their offspring.  Later, this idea was opposed by biologists. Darwinism is the most widely accepted theory of biological evolution. It was proposed by Charles Darwin (1809 – 1882), the British naturalist.

Mendel and His Contributions to Genetics:

The passing of characteristics from one generation to the next generation is referred to as heredity. Genetics refers to the study of genes and heredity. Gregor Johann Mendel (1822-1884), an Austrian biologist, is known as the “father of modern genetics.” He carried out many experimental studies on plant hybridization. His experimental studies on pea plants (Pisum sativum) are very popular among biologists.

His experiments provided a way for a clear understanding of the fundamental principles of inheritance. Mendel discovered three important laws of inheritance. Even before the discovery of genes and nucleic acids, Mendel described the transmission of genetic traits. His contributions laid the foundation of modern genetic studies.

Mendel’s Work:

Mendel carried out his research on heredity using garden peas (Pisum sativum). He studied the inheritance of seven different features in peas. He used seven pairs of contrasting characters to carry out his breeding experiment. The following characters were used by Mendel for his study.

1. Stem height
2. Flower color
3. Flower position
4. Pod shape
5. Pod color
6. Seed shape
7. Seed color

Mendel carried out artificial cross-pollination in pea plants which possessed contrast traits. He carried out cross-pollination by transferring pollen grains from one flower to another using a small brush. He grew a huge number of plants for each cross and collected enormous data for several generations.

For nine years, Mendel carried out his hybridization experiments. He published his findings in the year 1866. But his work was not recognized at this time. Later in the year 1900 (16 years after his death), three European scientists, namely Hugo de Vries, Carl Correns, and Erich von Tschermak, rediscovered his work.

Mendel’s Three Laws:

Based on his studies on inheritance, Mendel proposed three important laws.

1. Law of dominance
2. Law of segregation
3. Law of independent assortment

Law of Dominance

The law of dominance is known as the first law of inheritance. It states that: “When parent generation with a pair of pure contrasting alleles is crossed together, only one allele gets expressed in the next generation. Whereas the expression of other allele is prevented.

The allele which gets expressed in the hybrid is known as the dominant allele, whereas the unexpressed allele is known as the recessive allele. Dominant characters are found to appear in the F1 generation, whereas recessive characters are found to appear in the F2 generation.

Law of Segregation

The law of segregation is known as the second law of inheritance. It states that during gamete formation, genes get separated from each other, thereby allowing each gamete to carry one copy of the gene. During gamete formation, two members of single gene pair are never observed to occur in the same gamete. They always get separated and are passed on to different gametes.

Law of Independent Assortment

The law of independent assortment is known as the third law of inheritance. It states that during gamete formation, members of different gene pairs get assorted in a random fashion independent of each other. In other words, alleles of one gene do not influence the other.  Law of independent assortment plays an important role in producing new genetic combinations, thereby contributing to genetic diversity.