Chapter 12 Mendel and Heredity

12-1: Origins of Hereditary Science  Why was Gregor Mendel important for modern genetics?  Why did Mendel conduct experiments with garden peas?  What were the important steps in Mendel’s first experiments?  What were the important results of Mendel’s first experiments? Mendel is considered the father of modern genetics.

Mendel’s Experiments  Heredity is the study of inheritance  Genetics is the study of the science behind heredity and the mechanisms by which traits are passed from parents to offspring  Gregor Mendel Austria, monk, math professor, 1800’s  Pea plants Self pollinating, visible traits, many offspring, rapid generations, availability, easy to grow/care  Results Purple flower x white flower = ALL purple flowers Second generation = 75% purple, 25% WHITE

vocabulary Contrast  difference Character  recognizable, inherited feature or characteristic (hair color) Trait  possible forms of a character (the hair color could be brown, blonde, etc) Hybrid  offspring that are a cross between parents with contrasting traits BB x bb -----Bb Generation  entire group of offspring from a given set of parents

Monohybrid crosses  Study just one pair of contrasting traits  Mendel’s first experiment Self pollinate for many generations to insure purebred plants.. “true breeding”  Purple flowers or white flowers P generation with contrasting traits P parent, F 1 first filial, F 2 second filial generation Allow F1 to self pollinate Count number of each trait in each generation  Ratios PP x pp….. all Pp….. ¼ PP, 2/4 Pp, ¼ pp

12-2: Mendel’s Theory  What patterns of heredity were explained by Mendel’s hypothesis?  What is the law of segregation?  How does genotype relate to phenotype?  What is the law of independent assortment? Mendel’s theory explains why you have some, but not all of the traits of your parents.

Explaining Mendel’s Results Genotype  the combinations of genes that are possible and how many of each are expected (genotypic ratio) BB, Bb, bb 1BB: 2Bb: 1bb Phenotype  the physically expressed trait and the percentage of each trait that is expected (phenotypic ratio) ¾ or 75% brown* ¼ or 25% blonde * Both the BB and the Bb express ‘brownness’