The observations and conclusions that Mendel made from the monohybrid cross identified that inheritance of a single trait could be described as passage of genes (particles) from parents to offspring. Each individual normally contained two particles and these particles would separate during production of gametes. During sexual reproduction, each parent would contribute one of these particles to reconstitute offspring with 2 particles. In the modern language, we refer to the genetic make-up of the two “particles” (in this case, alleles) as the genotype and the physical manifestation of the traits as the phenotype. Therefore, Mendel’s first rues of inheritance are as follows:
- Law of Segregation
- During gamete formation, the alleles for each gene segregate from each other so that each gamete carries only one allele for each gene
- Law of Dominance
- An organism with at least one dominant allele will have the phenotype of the dominant allele.
- The recessive phenotype will only appear when the genotype contains 2 recessive alleles. This is referred to as homozygous recessive
- The dominant phenotype will occur when the genotype contains either 2 dominant alleles (homozygous dominant) or on dominant and one recessive (heterozygous)
