Mendel's Experiments and Heredity

Genetics is the study of heredity. Johann Gregor Mendel set the framework for genetics long before chromosomes or genes had been identified, at a time when meiosis was not well understood. Mendel selected a simple biological system and conducted methodical, quantitative analyses using large sample sizes. Because of Mendel’s work, the fundamental principles of heredity were revealed. We now know that genes, carried on chromosomes, are the basic functional units of heredity with the capability to be replicated, expressed, or mutated. Today, the postulates put forth by Mendel form the basis of classical, or Mendelian, genetics. Not all traits are transmitted from parents to offspring according to Mendelian genetics, but Mendel’s experiments serve as an excellent starting point for thinking about inheritance.

Sections

• Mendel’s Experiments and the Laws of Probability — the scientific reasons for the success of Mendel’s experimental work, the expected outcomes of monohybrid crosses between dominant and recessive alleles, and how the sum and product rules calculate probabilities.
• Characteristics and Traits — the relationship between genotype and phenotype in dominant and recessive gene systems, how a Punnett square predicts a monohybrid cross, the purpose of a test cross, and non-Mendelian patterns such as incomplete dominance, codominance, and sex linkage.
• Laws of Inheritance — Mendel’s laws of segregation and independent assortment in terms of meiosis, the forked-line method for calculating probabilities across multiple gene crosses, how linkage and recombination affect gamete genotypes, and the phenotypic outcomes of epistasis.

This chapter is adapted from Biology 2e, Chapter 12: Mendel’s Experiments and Heredity by Mary Ann Clark, Jung Choi, Matthew Douglas, and OpenStax, © OpenStax, licensed under CC BY-NC-SA 4.0. Access the original for free at openstax.org. Each section page records its own changes from the source. Changes: the chapter-opening photograph is the source’s, re-encoded for the web with its credit kept in the caption; its alt text is the source’s own description, kept as written since it already names what is shown without repeating the caption’s identification.