The Work of Gregor Mendel SECTION 11.1

Experiments of Gregor Mendel

u  Heredity

u  Set of characteristics that are passed from a parent to their offspring

u  Genetics

u  Scientific study of heredity.

u  Gregor Mendel

u  Austrian monk who studied science and mathematics at the University of Vienna.

u  Worked in a monastery/high school teacher and tended the monastery garden.

Mendel's Work with Garden Peas u  Mendel studied the flowers and became familiar

with their anatomy.

u  Garden peas reproduce sexually, so he was able to control when and where “fertilization” (joining of the reproductive cells) occurs.

u  Mendels plants were considered “true-breeding” which means they self-pollinate and produce offspring identical to themselves.

u All characteristics (traits) would be the same.

u  He studied 7 different contrasting traits and crossed the plants to produce plants that are considered “hybrids” or offspring with characteristics from both parents.

Genes & Alleles u  Genetic Crosses

u  P = Parental Generation u  F1 (first filial generation) = offspring of P generation u  Mendel discovered that all of the F1 offspring from

his initial crosses had the characteristic of ONLY one parent.

u  He formed 2 conclusions: u An individuals characteristics are determined by

factors that are passed from one parental generation to the next. These factors are called “genes”.

u  Some “alleles” (forms of a gene) are dominant and others are recessive. This is referred to as the Principle of Dominance.

u  Organisms with at least one dominant gene will exhibit that trait.

u  Organisms with a recessive allele will ONLY show that trait if NO DOMINANT ALLELE IS PRESENT.

Segregation u  Mendel also wondered if the recessive

alleles had simply disappeared or were they still present in the new plants (offspring).

u  To find out, he allowed the F1 plants to self pollinate and produce offspring. These offspring become the F2 generation.

u  Discovered the traits controlled by the recessive allele appeared again in the F2 generation.

u  Dominant allele masked the recessive allele

u  It reappeared because the recessive allele had separated (segregated) from the dominant allele.

u  Segregation must have occurred during the formation of “gametes”