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Introduction to Genetics Chapter 11 Genetics: • The scientific study of heredity • The study of how gametes (from meiosis) combine and which traits are expressed! History • Gregor Mendel- Austrian monk, teacher, and gardener • Studied heredity of pea plants – Which traits (color, texture, etc.) were expressed under different conditions and breeding situations • Drew two conclusions from his experiments Conclusion 1 • Biological inheritance is determined by factors that are passed down from one generation to the next. – These “factors” are called genes. – Every trait is controlled by one or more genes. • Different forms of genes are called alleles. • Example: eye color=trait blue, brown, green, hazel=alleles • Segregation is the separation of alleles during gamete formation---during meiosis!! Conclusion 2 • Some alleles are dominant, some are recessive. – If an organism has a dominant allele for a trait, that is the allele that will be expressed. – Example: Yellow peas are dominant over green peas. If the yellow pea allele is present even once, the peas will be yellow. How did Mendel do it? • Fertilization is the meeting of the gametes (in sexual reproduction). • True-breeding plants self-pollinate to produce exact copies of themselves (clones). • Cross-pollination occurs when gametes from two different individuals are combined. – Cross-pollination of individuals with different traits makes a hybrid. Mendel crossed pea plants to determine what traits would be expressed in the offspring. How Pollination works: Examples of Segregation: Aa A AA x Aa a A Aa Aa A a aa a A AA Aa a Aa aa • The first diagram shows segregation: each parent’s alleles separate and combine with the alleles of the other parent. • The second diagram is a Punnett Square. It is used to show the segregation of alleles and the probability of combinations. • What words can we use to describe this cross? Description: • Parents (Aa) are heterozygous: having two different alleles. • There is a 50% chance the offspring will also be heterozygous. • There is a 25% chance the offspring will be homozygous and recessive. (aa) • There is a 25% chance the offspring will have AA, which is homozygous and A dominant. (AA) – Homozygous: having two of the same a alleles. A a AA Aa Aa aa Phenotype and Genotype • Phenotype is a word used to described the physical characteristics expressed by the genes. (Think pheno=physical!) • Genotype is a word used to describe the genetic makeup of that characteristic. (Think geno=genes!) – Example 1: “TT” would be the genotype while “tall” would be the phenotype. – Example 2: “Tt” would be the genotype while “tall” would be the phenotype. Question: If A represents normal color and a represents albino: 1.Which is dominant…normal or albino? 2.What are the phenotypes of both parents? 3.What are the phenotypes of the four possible offspring? A a A AA Aa a Aa aa