Mendel is known as the founder of classical genetics and studied heredity by examining inheritance patterns in pea plants.
Mendel conducted experiments using true-breeding plants that always produced the same traits when self-fertilized.
Mendel crossed true-breeding plants that differed in a single trait, like seed texture, and observed the results.
This is called a monohybrid cross, and the true-breeding plants are the parental generation.
The offspring of the first filial generation exhibit only one parental trait, which is the smooth seed.
When the F1 generation was self-crossed, the resulting F2 generation showed a ratio of three smooth seeds to one wrinkled seed.
The traits were either smooth or wrinkled, and nothing in between.
Mendel observed this same result in many other monohybrid crosses, such as flower color, and used math and statistics to develop a theory.
Mendel proposed that traits are controlled by factors that occur in pairs and that the parental true-breeding plants can be designated as SS for the smooth seed plant and ss for the wrinkled seed trait.
During sex cell production, these factors separate into the pollen or ovum and combine in the offspring.
In a monohybrid cross, the parental, true-breeding plants produce sex cells, or gametes, of each type.
When the gametes unite, the resulting F1 generation has both types of factors, and one of them is dominant over the other, which is recessive.
In this case, the smooth seed trait is dominant over the wrinkled seed trait.
The F1 parents produce either S or s gametes, and a Punnett square can be used to depict the gametes and their possible unions.
In the F2 generation, three possibilities can result from the gametes joining: one SS, two Ss, and one ss, which determine the resulting traits of the offspring.
The phenotype of each trait is determined by the genotype of the factor pairs, and the phenotypic ratio of smooth seeds to wrinkled seeds is 3:1.
There are three types of factor pairs: one SS, two Ss, and one ss, which determine the genotypic ratio of 1:2:1.
The SS genotype is homozygous dominant, the Ss genotype is heterozygous, and the ss genotype is homozygous recessive.
Mendel's monohybrid crosses supported his theories, and he proposed the Principle of Segregation, which states that the two members of a gene pair segregate from each other in the formation of gametes.
This means that both types of factors are equally represented in the gametes, even though S is dominant over s in terms of the resulting trait.
