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Download Mendelian Genetics - Edmonds School District
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Mendelian Genetics 1 Gregor Mendel (1822-1884) • Father of genetics • Austrian Monk • Between 1856 – 1863 he studied ~28,000 pea plants • Importance of his work not realized until 20th century, ~20 years after death 2 Mendel’s Experiments 3 The Peas • Advantages of Pea Plants: – Grown in small areas – distinct heritable features – Each feature has two variants – Lots of offspring – Can self-fertilize or cross fertilize 4 Reproduction in Flowering Plants • Pollen (produced by stamen) contain sperm • Ovary contains egg • Pollen grows tube down style to carry sperm to egg • Self-fertilization - sperm and egg from same flower • Cross-fertilization - sperm and egg from different flower 5 His Experiments • First created truebreeding peas by allowing them to selffertilize • True breeding = only produces offspring with one specific trait 6 His Experiments • Then, he cross-fertilize (hybridized) two contrasting, true-breeding varieties (P1 generation - parent) • Offspring is the F1 Generation – first filial • Then allowed the F1 hybrids to self-pollinate to produce an F2 generation – 2nd filial 7 His Experiments P1 Generation F1 Generation All tall F1 Generation F2 Generation 3 tall, one short 8 His Experiments • Results: • F1 generation: all dominant phenotypes • F2 generation: 3:1 ratio of dominant to recessive phenotypes 9 His Experiments • Created three Laws of Inheritance – Law of Dominance – Law of Segregation – Law of Independent Assortment 10 Mendel’s Laws of Inheritance 11 Law of Dominance • In a cross of true-breeding parents, only one form of the trait will appear in the next generation • The apparent trait is dominant, the other is recessive 12 Law of Segregation • The pair of factors (alleles) is segregated, or separated, during formation of gametes (sperm and egg) 13 Law of Independent Assortment • Factors (alleles) for different traits are distributed in gametes independently of each other 14 Applying Mendel’s Laws – Punnet Squares • Two types – used to show expected genotype of offspring • Monohybrid – 2 gametes from each parent – 2x2 grid • Dihybrid – 4 gametes from each parents – 4x4 grid 15 Applying Mendel’s Laws – Test Cross • A mating between an organism with unknown genotype and a homozygous recessive organism • Example: – Mice can either be brown (B) or white (b). You have a mouse with a brown coat. – Can be BB or Bb – If Bb: offspring half brown/half white – If BB: offspring all brown 16
