Mendel's first law gave rise to the concept of recessive and dominant markers
Gregor Mendel observed that some tall pea plants when self–fertilized produce seeds that all grow into tall plants. The seeds of others give a mixture of tall and short plants. Mendel summarized his findings in two laws: the Law of Segregation and the Law of Independent Assortment.
Law of segregation: This law states that members of a pair of homologous chromosomes separate during the formation of gametes and are distributed to different gametes so that every gamete receives only one member of the pair.
Whichever of the two alleles in the offspring is dominant determines how the offspring expresses that trait (e.g. the color of a plant, the color of an animalPo's fur, the color of a person's eyes). More precisely, the law states that when any individual produces gametes, the copies of a gene separate so that each gamete receives only one copy (allele). A gamete will receive one allele or the other. For example, in meiosis, the paternal and maternal chromosomes get separated and the alleles with the traits of a character are segregated into two different gametes. If we put together, the two coexisting alleles of an individual for each trait segregate (separate) during gamete formation, so that each gamete gets only one of the two alleles. Alleles again unite at random fertilization of gametes.
The Law of Independent Assortment, also known as "Inheritance Law" or Mendel's Second Law
States that the inheritance pattern of one trait will not affect the inheritance pattern of another. Mendel's experiments with mixing two traits (dihybrid cross) showed 9 : 3 : 3 : 1 ratios which suggests that each of the two genes are independently inherited with a 3:1 ratio. Mendel concluded that different traits are inherited independently of each other, so that there is no relation. Law of independent assortment: The Law of Independent Assortment, also known as "Inheritance Law" or Mendel's Second Law, states that the inheritance pattern of one trait will not affect the inheritance pattern of another. Mendel's experiments with mixing two traits (dihybrid cross) showed 9 : 3 : 3 : 1 ratios which suggests that each of the two genes are independently inherited with a 3:1 ratio. Mendel concluded that different traits are inherited independently of each other, so that there is no relation.
Independent assortment occurs during meiosis in eukaryotic organisms, to produce a gamete with a mixture of the organism's maternal and paternal chromosomes. This process along with chromosomal crossover aids in increasing genetic diversity by producing novel genetic combinations.
Non-Mendelian inheritance: The inheritance of characteristics is not always as simple as it is for the characteristics that Mendel studied in pea plants. Each characteristic Mendel investigated was controlled by one gene that had two possible alleles, one of which was completely dominant to the other. This resulted in just two possible phenotypes for each characteristic. Each characteristic Mendel studied was also controlled by a gene on a different (nonhomologous) chromosome. As a result, each characteristic was inherited independently of the other characteristics. Geneticists now know that inheritance is often more complex than this.
Co-dominance/Intermediate inheritance: Inheritance in which the phenotype of the heterozygote falls between that of either homozygote.
Polygenic traits: Polygenic traits are controlled by two or more than two genes (usually by many different genes) at different loci on different chromosomes. These genes are described as polygenes. Examples of human polygenic inheritance are height, skin color and weight. Polygenes allow a wide range of physical traits. For instance, height is regulated by several genes so that there will be a wide range of heights in a population.
An example for Multiple alleles: A person's blood group may be either A, B, AB, or O.
Multiple alleles: Genes may have more than two allelic forms and the blood group in humans, for instance, is determined by multiple alleles of a single gene. There are four possible phenotypes for this character: A person's blood group may be either A, B, AB, or O.
Epistasis: In epistasis (from the Greek for "stopping"), a gene at one locus alters the phenotypic expression of a gene at a second locus.
Pleiotropy: The single gene controlling or influencing multiple (and possibly unrelated) phenotypic traits.