Mendel’s Work

Gregor Mendel Gregor Mendel was a young priest from a monastery in Central Europe where he cared for the garden and began experimenting with pea plants. He noticed that the pea plants had different physical characteristics, or traits. Tall plants and short plants. Green seeds and yellow seeds.

Gregor Mendel He also noticed that the characteristics of the pea plants resembled those of the parent plants. This passing of traits from parents to offspring is called heredity. Mendel worked with thousands of pea plants to understand the process of heredity. Mendel’s work formed the foundation of genetics, the scientific study of heredity.

Why Pea Plants? Mendel studied pea plants because they were self-pollinating. This means that the pollen from one flower lands on the pistil of the same flower. He developed a method to cross-pollinate by removing the pollen from one plant and brushing onto a second plant.

Mendel’s Experiments Mendel started his experiment with purebred plants. A purebred plant is one that always produces offspring with the same form of a trait as the parent. A purebred short plants always produce short offspring.

Mendel’s First Experiment Mendel first crossed a purebred short plant with a purebred tall plant. He called these two plants the parental (P) generation. He called the offspring the first filial generation or the (F1) generation. To Mendel’s surprise, all the offspring were tall.

Mendel’s Second Experiment Mendel then took the offspring in the F1 generation and crossed them. These results also surprised Mendel. The offspring in the second filial generation or (F2) were a mix of tall and short plants. He found that 75% were tall and 25% were short.

Genes and Alleles Mendel also tested many other traits in pea plants. The factors that control traits are called genes. Different forms of a gene are called alleles For example the gene for stem height can be determined by a short allele or tall allele.

Dominant and Recessive Alleles Individual alleles control the inheritance of traits. Some alleles are dominant and others are recessive. The dominant allele is one whose trait always shows up in the organism when the allele is present. A recessive allele is one that will be masked whenever the dominant allele is present and will only show up if there are two recessive alleles.

Using Symbols for Dominant and Recessive Alleles In order to represent the two alleles in a genetic cross, scientists use a shorthand method for dominant and recessive. Instead of using words like “tall stems” they use letters. Dominant alleles are represented with a capital letter. Tall stems = (T) Recessive alleles are represented with the same letter, only its lowercase. Short stems = (t)

Understanding Mendel’s Crosses Mendel’s P generation plants were purebred, meaning they had two of the same alleles. (TT) = “purebred tall” (tt)= “purebred short” The F1 offspring received one allele from each parent making the allele combination: (Tt) A hybrid is an organism that has both the dominant and the recessive allele for a trait.

Mendel’s Contribution Many scientists thought that Mendel’s explanation of heredity was oversimplified. Because of this, his work was forgotten for 34 years. However years later, three other scientists confirmed his findings and he became known as “The Father of Genetics”