Mendel's Lesson in Inhertiance

The Work of Gregor Mendel Sec. 11-1, 11-2, 11-3 The science of genetics owes its basic information to Gregor Mendel. He knew that flowers had male and female parts, and he understood how flowers were fertilized. He noticed the peas he had were true breeding, meaning he always got peas that were just like the parents if they were allowed to self-pollinate. Genes and Dominance Gregor studied peas with different traits, or characteristics. He crossed plants of different traits to produce hybrids. Mendel’s first conclusion: Hybrids, F1 generation, were not a blend of the parents. From this fact it was determined that traits are passed to offspring by something named genes, and there are 2 forms of each genes, called alleles. Mendel’s second conclusion: Principle of Dominance….some alleles are dominant over others (called recessive) Mendel wanted to know where the recessive alleles went so he self-pollinated the F1 plants and found it to reappear in the ratio of 1:4 He explained this by theorizing that alleles are inherited independent of each other ( they are segregated from each other during gamete formation…meiosis). Probability studies are used to determine inheritance. Punnett Squares were developed to determine the probability of inheritance in a cross. An organism with the same alleles for a trait is homozygous. An organism with 2 different alleles for the same trait is heterozygous. The physical appearance of an organism is its phenotype. The genetic makeup of an organism is its genotype. Independent Assortment Alleles (genes that correspond to different variations of a trait) segregate independently of one another during gamete formation (meiosis). This is why there are so many variations of in organisms. Inheritance continued…. Some traits are neither dominant nor recessive and many are controlled by multiple genes. • Incomplete Dominance: the heterozygous phenotype is between the 2 homozygous phenotypes • Codominance: in the heterozygous genotype both traits show in the phenotype • Multiple alleles: there are some genes that have more than 2 variations…example human blood type • Polygenic traits: some phenotypes are the result of several different genes…..example human skin color Remember….genes provide the plan for an organism, but environment also plays a role in the characteristics of an organism.