Mendelian Genetics

Mendelian Genetics is a kind of biological inheritance that highlights the laws proposed by Gregor Mendel in 1866 and rediscovered in 1900. These laws faced a few controversies initially but when Mendel’s theories got integrated with the chromosome theory of inheritance, they soon became the heart of classical genetics. Later, Ronald Fisher combined these ideas with the theory of natural selection and forms a base for population genetics and modern evolutionary synthesis.

Table of Contents

• Mendel’s Experiments
• Mendel’s Laws of Inheritance
• Law of Segregation
• Law of Independent Assortment
• Law of Dominance

Gregor Mendel performed breeding experiments in his garden to analyse patterns of inheritance. He opted for cross-bred normal pea plants with selective traits over various generations. When two plants were crossed that differed in a single trait (round peas vs. wrinkled seeds, short stems vs. tall stems, white flowers vs. purple flowers, etc), Mendel found that the next generation, F1 comprised of whole individuals that exhibit only one trait. However, after the generation was interbred, its offspring which is the F2 generation showed a 3:1 ratio wherein three individuals had similar traits like a parent.

Mendel theorized that genes could be formed by three possible combinations of heredity units that are said to be factors: AA, aa, Aa. The big ‘A’ shows the dominant factor and the small ‘a’ shows the recessive factor. The beginning plants were homozygous AA or aa, F1 generation was Aa and F2 generation was AA, aa or Aa. The interaction between these two finds the physical trait that is visible.

According to Mendel’s law of Dominance, when two organisms of separate traits are crossed, every offspring shows the trait of only one dominant character. The recessive trait is expressed phenotypically only if both factors are recessive.

Also Read: Non-Mendelian Inheritance

Mendel’s conclusions could be described in the following principles:

According to the law of segregation, every parent’s pair of genes or alleles divide and a single gene passes from every parent to an offspring. Which particular gene passes on in a pair is entirely up to chance.

According to the law of Independent Assortment, discrete pairs of alleles pass onto the offspring without depending on one another. Hence, the inheritance of genes at a particular region in a genome does not affect the inheritance of genes in a different region.

According to the law of dominance, recessive alleles are always masked by dominant alleles. Hence, a cross between a homozygous recessive and a homozygous dominant shows the dominant phenotype by still having a heterozygous genotype. This law could be explained by the monohybrid cross experiment. In the case of a cross among the two organisms with contrasting traits, the character that is visible in the F1 generation is known as dominant and the one that is suppressed is known as recessive. Every character is handled by a pair of dissimilar factors and only one among the characters shows the results. Please note that the law of dominance is true but not applicable from a global perspective.

• Evolution
• Endangered Species