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Transcript
Introduction to Genetics Chapter 11 The Work of Gregor Mendel Section 11.1 The Experiments of Mendel • Heredity is the delivery of characteristics from parent to offspring. • Scientific study of heredity is genetics. • Austrian monk Gregor Mendel is the father of genetics. – Used pea plants (a model system) The Experiments of Mendel • The Role of Fertilization – Fertilization is when male/female reproductive cells join to make a new cell. – Pea plants normally self pollinate “true breeding” • Offspring identical – Each plant had certain traits. • These traits may vary between individuals. The Experiments of Mendel • Mendel crossed his “true breeding” plants to see how traits would be expressed. • He studied 7 different traits. – Each had two contrasting characters. • Offspring of a cross between different parents are called hybrids. The Experiments of Mendel • Genes and Alleles – Each original pair of plants is the P generation. – Offspring are F1 = first filial – Genes are the factors (traits) passed from one generation to the next. – Alleles are alternative forms of a gene. The Experiments of Mendel • Dominant and Recessive Alleles – Principle of Dominance (Mendel’s 2nd Conclusion) • Dominant: trait will show if one allele present (masks other allele) • Recessive: need two alleles for trait to appear Segregation • Mendel didn’t stop with crossing the parent plants. • He thought: Where did the recessive alleles go? • He allowed all 7 kinds of plants to self pollinate. – Called these the F2 Segregation • The F1 Cross – The F2 plants showed the recessive alleles! • ¼ of the plants showed this trait. – How could this be? • At some point, the recessive allele had separated from the dominant. • Another word for separation=SEGREGATION – Alleles segregate during the formation of gametes. Segregation • During gamete formation, the alleles for each gene segregate. • Each gamete carries only one allele for each gene.