Mendelian inheritance

Gregor Mendel

Gregor Mendel - characteristics of pea plants - english

Dominant-recessive inheritance - flowers of pea plants

Mendel-flowers

Dominant-recessive inheritance P - F1 - F2

Intermediate inheritance P - F1 - F2

Mendelian inheritance refers to the patterns of inheritance of traits and genes that were first identified by Gregor Mendel in the 19th century. Through his work on pea plants, Mendel discovered that traits are inherited in predictable ways from parents to offspring. His findings laid the foundation for the field of genetics and are fundamental to understanding how traits are passed down through generations.

Principles of Mendelian Inheritance

Mendelian inheritance is based on three key principles:

Law of Segregation

The Law of Segregation states that every individual possesses two alleles for each gene, one inherited from each parent. These alleles segregate (separate) during the formation of gametes (sperm and eggs), ensuring that each gamete carries only one allele for each gene. This principle explains why offspring may inherit one of several traits from their parents.

Law of Independent Assortment

The Law of Independent Assortment describes how alleles of different genes are distributed independently of one another from parents to offspring. This means the inheritance of an allele for one trait does not influence the inheritance of an allele for another trait, provided the genes are on different chromosomes or far apart on the same chromosome.

Law of Dominance

The Law of Dominance states that when two different alleles are present in an organism, one may be dominant and the other recessive. The dominant allele is expressed in the organism's phenotype, while the recessive allele is not, unless the organism is homozygous for the recessive allele.

Extensions and Modifications

While Mendel's principles provide a framework for understanding genetic inheritance, later research has shown that inheritance can be more complex due to factors such as codominance, incomplete dominance, and polygenic inheritance. Additionally, linkage occurs when genes are located close together on the same chromosome, leading to an exception to the law of independent assortment.

Genetic Disorders and Mendelian Inheritance

Many genetic disorders follow Mendelian inheritance patterns. These can be categorized into autosomal dominant, autosomal recessive, X-linked dominant, and X-linked recessive disorders, depending on the affected gene's location and whether the trait is dominant or recessive.

Impact on Modern Genetics

Mendel's work, though initially overlooked, was rediscovered at the turn of the 20th century and has since been recognized as the foundation of classical genetics. His principles have been applied in various fields, including genetic counseling, plant and animal breeding, and molecular biology, to predict the inheritance of traits and understand the genetic basis of diseases.