MENDEL’S WORKObjectivesWhat were the results of Mendel’s experimentsor crosses?What controls the inheritance of traits inorganisms?
Mendel’s Work Mendel experimented with thousands of Pea plants looking at their different traits to understand the process of heredity. His discoveries form the foundation of genetics. Heredity –the passing of physical characteristics from parents to offspring Trait- each different form of a characteristic Genetics – the study of heredity
Mendel’s Experiments Flowering Plant anatomy Pistil – produces the female sex cells or eggs Stamens – produce pollen which contains the male sex cells or sperm Fertilization is when the egg and sperm join forming a new organism In plants the pollen must reach the pistil for fertilization to occur. This is called pollination
Pollination Pea plants usually self- pollinate. The pollen from their stamens lands on the same plants pistils. Mendel developed a method to cross-pollinate pea plants. He took pollen from one pea plant and brushed it into the pistil of another.
Crossing Pea Plants Mendel crossed plants with contrasting traits Ex. Tall plants with short plants Started with purebred plants a purebred organism is one who is the offspring of many generations of that have the same trait
The F1 Offspring Mendel crossed purebred tall with purebred short Parental (P) generation Tall x short Offspring from the cross are called F1 (filial) All F1 offspring were tall
F2 offspring When F1 were full grown, Mendel allowed them to self-pollinate F were a mix of tall 2 and short ¾ were tall and ¼ were short
Experiments with Other Traits Mendel crossed pea plants with other contrasting traits such as seed shape, seed color, seed coat color, etc. In all crosses the F1 generation had only 1 form of the trait In the F2 generation the “lost” form reappeared in ¼ of the plants.
Dominant and Recessive Alleles Mendel’s Conclusion factors control the inheritance of traits in peas. They exist in pairs The female parent contributes one factor and the male parent contributes the other factor One factor in a pair can mask or hide the other
Genes and Alleles Genes – factors that control a trait Alleles – different forms of a gene An organism traits are controlled by the alleles it inherits from its parents. Some alleles are dominant, while others are recessive Dominant allele – trait always shows Recessive allele –trait is hidden whenever dominant allele is present
Alleles in Mendel’s Crosses Stem Height Cross P generation tall tall x short short F1 generation all were tall short- Look tall F2 generation: ¼ tall tall - look tall ¼ tall short + ¼ short tall – look tall ¼ short short – look short
Symbols for alleles Letters are used to represent alleles Capital letters are used for dominant alleles Lowercase letters are used for recessive alleles Purebred tall = TT Purebred short = tt Hybrid (one of each) =Tt
Significance of Mendel’s Contribution Before Mendel most people thought that the traits of an individual were a blend of their 2 parents. If they blended the Tt plants should be medium height Mendel found out that traits are determined by individual alleles some of which are dominant and some recessive. Recessive traits may seem to disappear in the offspring only to reappear in the next generation Mendel’s work was not recognized during his lifetime, but was rediscovered in 1900. He is now considered the Father of Genetics.