IX. Genetics - You and your genes 2 Posted SV.pdf - IX.2...

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IX.2 Genetics and Heredity Heredity is the transmission of traits from one generation to the next. Genetics is the scientific study of heredity. Gregor Mendel worked on inheritance of traits in pea plants in the 1860s discovered the fundamental laws of inheritance 1. Law of segregation – each inherited trait is determined by a pair of genes, which are separated to the sex cells. Offspring thus inherit one copy (allele) of the gene from each parent when sex cells unite during fertilization 2. Law of independent assortment – genes for different traits are sorted separately, thus inheritance of one trait is independent of the inheritance of another 3. Law of dominance – an organism with alternate forms of a gene will express the form that is dominant Gregor Mendel
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Mendel’s technique for cross- fertilizing pea plants Analyzing patterns of inheritance Mendel created purebred varieties of plants and crossed two different purebred varieties. Hybrids are the offspring of two different purebred varieties. a. The cross-fertilization itself is referred to as a genetic cross . b. The parental plants are the P generation . c. Their hybrid offspring are the F 1 generation . d. A cross of the F 1 plants forms the F 2 generation . Terminology used by Mendel
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The seven characters of pea plants studied by Mendel Dominant Recessive Flower color Purple White Flower position Axial Terminal Seed color Yellow Green Seed shape Round Wrinkled Dominant Recessive Pod shape Inflated Constricted Pod color Green Yellow Stem length Tall Dwarf
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Purple flowers F 1 Generation White flowers P Generation (purebred parents) All plants have purple flowers F 2 Generation Fertilization among F 1 plants (F 1 ´ F 1 ) of plants have purple flowers of plants have white flowers 3 4 1 4 Mendel’s experiment on monohybrid crossing of two pure bred pea plants
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P Generation Genetic makeup (alleles) Alleles carried by parents Gametes Purple flowers PP White flowers pp All P All p p P F 1 Generation (hybrids) F 2 Generation (hybrids) Alleles segregate Gametes Purple flowers All Pp 2 1 2 1 Sperm from F 1 plant Eggs from F 1 plant Phenotypic ratio 3 purple : 1 white Genotypic ratio 1 PP : 2 Pp : 1 pp p p P P
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