Mendel and his Peas Chapter 5 Lesson 1 Chapter 5: Genetics How are traits passed from parents to offspring? Mendel and his Peas • Why did Mendel perform crosspollination experiments? • What did Mendel conclude about inherited traits? • How do dominant and recessive factors interact? Gregor Mendel the father of genetics Genetics the study of how traits are passed from parents to offspring (the study of inheritance) Heredity the passing of traits from parents to offspring Trait: a genetically determined characteristic or condition Gregor Mendel Mendel's work was done about 140 yrs. ago, but even now much of what we know about genetics is based on Mendel's work and illustrated by it. Gregor Mendel was born in 1822 on a farm in Heinzendorf, Austria At age 21 entered the Augustinian order of the Roman Catholic Church As a monk he - studied science at the University of Vienna and became an excellent mathematician Gregor Mendel As a school teacher - he engaged in many scientific activities At a monastery - he began a program of selective breeding of peas. After 8 yrs. of raising 30,000 pea plants and recording and classifying many pages of notes, he wrote a paper with his conclusions called Mendelian Genetics (1865). Mendel’s Experimental Methods Mendel studied genetics by doing controlled breeding experiments with pea plants. There are two types of pollination: • self-pollination • cross-pollination Self-Pollenation Mendel’s Experimental Methods When a true-breeding (purebred) plant self-pollinates, it always produces offspring with traits that match the parent. Mendel crosspollinated pea plants himself and recorded the traits that appeared. Cross-Pollenation Mendel’s Experimental Methods Why did Mendel perform crosspollination experiments? Mendel’s Results Once Mendel had enough truebreeding plants for a trait he wanted to test, he cross-pollinated selected plants. Plants are called hybrids if they come from true-breeding parent plants with different forms of the same trait. First-Generation Crosses Mendel’s Results hybrid Science Use the offspring of two animals or plants with different forms of the same trait Common Use having two types of components that perform the same function, such as a vehicle powered by both a gas engine and an electric motor Mendel’s Results Mendel also cross-pollinated hybrid plants. He observed that offspring of hybrid crosses always showed traits in a 3:1 ratio. Second-Generation (hybrid) Crosses Mendel’s Results Mendel recorded traits of offspring from many hybrid crosses. Mendelian Genetics His paper was the first recorded study of how traits pass from one generation to the next. Mendel also was the first to use the mathematics of probability to explain heredity. Mendelian Genetics When Mendel's paper was published, in 1865, it received little attention, and was rarely cited by botanists or biologists during the next 34 years. In 1900, Mendel's work was cited by three botanists, writing in different parts of Europe: Hugo de Vries, in Amsterdam; Carl Correns, in Tübingen; and Eric Von Tcshermak, in Esslingen, Austria. Mendel's Theories the concept of unit characteristics the concept of dominant and recessive the concept of segregation the concept of unit characteristics Mendel concluded that two factors, one from the sperm and one from the ovum, control each inherited trait. if factors were the same - purebred TT (tall) tt (short) if factors were not the same - hybrid Tt (tall) The Concept of Dominant and Recessive Dominant trait - a genetic factor that blocks another genetic factor. Recessive trait - a genetic factor that is blocked by the presence of a dominant factor. The dominant allele (factor) completely masks the presence of the recessive allele (factor). the concept of segregation Mendel reasoned that when a cell forms gametes, the genes separate (segregate) so that there is only 1 gene for each characteristic in each gamete. Principles of Heredity 1. Traits are controlled by alleles on chromosomes. 2. An allele’s effect is dominant or recessive. 3. When a pair of chromosomes separates during meiosis the different alleles for a trait move into separate sex cells.