Mendel's Experiments FAQ

In a monastery garden, Austrian scientist and an Augustinian friar Gregor Mendel invented the science of genetics. He performed experiments on pea plants that demonstrated the laws of inheritance beginning in 1856, long before anyone knew the existence of genes or DNA.

After high school, Mendel joined a monastery dedicated to teaching and scientific research. He spent years as a teacher, while investigating the principles of inheritance. Eventually, he became an abbot and turned his mind to administration and politics. His scientific ideas were neglected in his lifetime, but he is now considered the father of genetics.

Mendel's Laws

Mendel's Laws have been amended slightly but stand firm. Modern geneticists use the term 'gene' where Mendel said 'factor.' He also used the word allele to describe one of the forms of a gene, as in an allele for white pea flowers as opposed to purple.

  • The Law of Segregation: During reproduction, the two alleles for a trait separate from each other; alleles for traits are recombined at fertilization, determining the traits of the offspring. What Mendel formulated is exactly what happens during reproduction. Genes cross over and divide, and only half of each parent's genes become the blueprint for the new organism.
  • The Law of Independent Assortment: Alleles for different traits are inherited independently of one another. Mendel found that pea plant color was inherited separately from pea plant height, for example, and the one trait did not affect the other. (It turns out that some traits do tend to be inherited together, but again, Mendel's principle generally stands.)
  • The Law of Dominance: In a cross of parents that are pure for a trait, only one form of the trait will appear in the next generation. Mendel found that crossing a genetically pure tall pea plant and a genetically pure short pea plant will produce only a tall pea plant in the next generation, not a midsize one. (It turns out some traits are not ruled so strictly by dominance, but many are.)

Dominant and recessive genes

For many traits, organisms inherit two different alleles-forms of a gene-but show only one. Mendel noticed this dominance in the pea plants he studied (which were tall or short) and in certain pea flowers (which were purple or white). The traits did not blend.

Eye color

Eye color inheritance isn't as simple as once believed. Though most people have brown eyes, and blue eye color is recessive, at least 16 genes affect eye color in one way or another. Gray eyes, green eyes, green eyes with a brown center, and blue eyes with touches of brown are caused by variations in genes. Many genes influence eye color, which is why people's eyes do not look exactly alike.

How could Mendel study inheritance without knowing about genes?

He knew about math, and he knew about logic. He observed effects closely and reasoned out what their causes might be. Then, he performed more experiments to verify his results. He took enormous pains and kept records with scientific accuracy. His results are a measure of his genius.

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