Concept of Gregor Johann Mendel


Gregor Johann Mendel (1822-1884)



Father of Genetics:

Gregor Mendel, through his work on pea plants, discovered the fundamental laws of inheritance. He deduced that genes come in pairs and are inherited as distinct units, one from each parent.


Mendel tracked the segregation of parental genes and their appearance in the offspring as dominant or recessive traits. He recognized the mathematical patterns of inheritance from one generation to the next.

Mendelian Inheritance:

Mendelian inheritance refers to patterns of inheritance that are characteristic of organisms that reproduce sexually.


Mendelian Laws:

Mendelian Laws of inheritance are usually stated as:

1) The Law of Segregation:

Each inherited trait is defined by a gene pair. Parental genes are randomly separated to the sex cells so that sex cells contain only one gene of the pair. Offspring therefore inherit one genetic allele from each parent when sex cells unite in fertilization.

2) The Law of Independent Assortment:

Genes for different traits are sorted separately from one another so that the inheritance of one trait is not dependent on the inheritance of another.

3) The Law of Dominance:

An organism with alternate forms of a gene will express the form that is dominant.

Dominance refers to the relationship between two versions of a gene. Individuals receive two versions of each gene, known as alleles, from each parent. If the alleles of a gene are different, one allele will be expressed; it is the dominant gene. The effect of the other allele, called recessive, is masked.


e.g. dominance, in genetics, greater influence by one of a pair of genes (alleles) that affect the same inherited character. If an individual pea plant with the alleles T and t (T= tallness, t = shortness) is the same height as a TT individual, the T allele (and the trait of tallness) is said to be completely dominant.


Types of Dominance:

There are different types of dominance:

  • incomplete dominance
  • co-dominance
  • complete dominance


  • Incomplete dominance is a condition in which a dominant allele does not completely mask the effects of a recessive allele. For example, the pink color of flowers (such as snapdragons or four o’clock flowers), the shape of hairs, hand sizes, voice pitch in humans.


  • Co dominance essentially means that no allele can block or mask the expression of the other allele. An example in humans would be the ABO blood group, where alleles A and alleles B are both expressed. So if an individual inherits allele A from their mother and allele B from their father, they have blood type AB.


  • Complete dominance is a form of dominance where the dominant allele completely masks the effect of the recessive allele in heterozygous conditions. e.g. Brown eyes, for example, is a trait that exhibits complete dominance: someone with a copy of the gene for brown eyes will always have brown eyes. Blue eyes, on the other hand, are recessive: if a copy of the gene for brown eyes is present, the blue-eyed gene will be completely masked.


Multiple alleles it is a type of non-Mendelian inheritance pattern that involves more than just the typical two alleles that usually code for a certain characteristic in a species. An excellent example of multiple allele inheritance is human blood type. Blood type exists as four possible phenotypes: A, B, AB, & O. There are 3alleles for the gene that determines blood type. (Remember: You have just 2 of the 3 in your genotype 1 from mom and 1 from dad).

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