Heredity

The Beginnings of Heredity Ever since humans began domesticating plants and animals (at least 10,000 years ago), people have wondered how traits were passed from parent to offspring. One belief was that traits were stored as 'particles' in the parts of each parent's body and 'blended' in the offspring. This theory left many questions unanswered, however.

Early Study of Genetics In 1851, Gregor Mendel experimented with pea plants to see why they had different characteristics or traits. Johann Gregor Mendel was born in Hyncice (in what is now the Czech Republic) on July 22, 1822 Republic.. In 1843, at the age of 21, Mendel became a friar at the Augustinian monastery in Brno, Czechoslovakia, a center of learning whose members studied theology, philosophy and natural sciences. For more than ten years, Mendel experimented with thousands of plants and worked out the foundation of genetics, the study of heredity. Heredity – the passing of traits from parent to offspring.

Dominant and Recessive Alleles From his results, Mendel reasoned that individual factors must control the inheritance of traits. Allele – a particular form that a gene may have for a trait (think of alleles as the different versions) Dominant allele – trait that, if present, is shown and is represented by capital letters Recessive allele – trait that is covered up by a dominant allele and is represented by lowercase letters

Phenotypes and Genotypes Two useful terms that help geneticists describe organisms are: Phenotype - the trait that is shown in an individual (tall or short, brown eyes or blue eyes, etc.) Genotype - the genetic makeup of an individual’s trait (ex: TT, Tt or tt)

Describing Genotypes There are two terms that geneticists use to describe an organisms genotype. Homozygous – two of the same alleles This is also known as a purebred. Heterozygous - a dominant allele paired with a recessive allele This is also known as a hybrid.

Co-dominance One trait is not always dominant over the other. For some alleles, co-dominance takes place. In co-dominance, the alleles are neither dominant or recessive, but they mix to giver another phenotype.