Gregor Mendel and the Fundamental Laws of Genetics

The Life and Legacy of Gregor Mendel

Gregor Mendel, an Austrian-born biologist, established the laws governing heredity. He presented his work in 1866, but it was initially ignored because it was produced while scientists were primarily focused on classifying animals and plants. After being ignored, in 1868 he was devoted to religion. American researchers, about 30 years later, named him when they were to publish their work and realized that Mendel had reached the same conclusions. In his honor, these principles were called Mendel's Laws.

Key Genetic Concepts and Definitions

• Genetics: The part of biology that studies how hereditary traits are transmitted.
• Purebred: When the two alleles for a given character are equal.
• Alleles: One of the variations that a gene can have.
• Dominant: An allele that always occurs and is written in capital letters.
• Recessive: An allele that, in the presence of the dominant, is not expressed and is lower-cased.
• Equipotent: When the result of both alleles is intermediate.
• Hybrid: When the two alleles for a particular trait are different.
• Homozygous: When the two alleles for a particular trait are equal.
• Heterozygosis: Same as hybrid; having different alleles for a trait.
• P Generation: The parental generation from crossing two pure races.
• F1 Generation: Results from crossing two pure breeds.
• F2 Generation: The result of crossing two individuals of the F1 generation.
• Genotype: The set of all characters that an individual has, whether manifested or not.
• Phenotype: The characters that an individual exhibits or are patent.
• Retrograde Crossing: Crossing an individual with a homozygous recessive. 100% identical offspring indicates purebred offspring. A 1/2 to 1/2 ratio indicates a hybrid.

Mendel's Three Laws of Inheritance

1st Law: Law of Uniformity

The law of uniformity of hybrids of the first filial generation states: If you cross two pure breeds that differ in one character, the descent is uniform, showing all the dominant character.

2nd Law: Law of Segregation

The law of segregation of characters in the second filial generation states: The recessive traits that do not manifest in the 1st filial generation reappear in the second filial generation in a ratio of three dominant to one recessive.

3rd Law: Principle of Independent Combination

In heterozygotes for two or more characters, each character is transmitted to the following filial generation independently of any other character. For this reason, all combinations are available for these characters.

Intermediate Inheritance and Incomplete Dominance

In all the characters studied by Mendel, there was an absolute dominance of one allele (dominant) over a recessive one, so that in the heterozygous phenotype, the dominant trait is observed. In some cases, intermediate inheritance occurs, meaning the heterozygote has an intermediate phenotype between the two parents. In the intermediate inheritance of crossing two hybrids, the ratio is 1:2:1. In dominant inheritance, the result of crossing two hybrids (phenotype) is in a 3:1 proportion.