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2. 2 Gregor Mendel Austrian monk  Studied science and mathematics at University of Vienna  Conducted breeding experiments with the garden pea Pisum sativum  Carefully gathered and documented mathematical data from his experiments Formulated fundamental laws of heredity in early 1860s  Had no knowledge of cells or chromosomes  Did not have a microscope

3. Mendelian Inheritance 3 Blending Inheritance Theories of inheritance in Mendel’s time:  Based on blending  Parents of contrasting appearance produce offspring of intermediate appearance Mendel’s findings were in contrast with this  He formulated the particulate theory of inheritance  Inheritance involves reshuffling of genes from generation to generation

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7. 7 Law of Segregation Each individual has a pair of factors (alleles) for each trait The factors (alleles) segregate (separate) during gamete (sperm & egg) formation Each gamete contains only one factor (allele) from each pair Fertilization gives the offspring two factors for each trait

8. Mendelian Inheritance 8 Modern Genetics View Each trait in a pea plant is controlled by two alleles (alternate forms of a gene) Dominant allele (capital letter) masks the expression of the recessive allele (lower- case) Alleles occur on a homologous pair of chromosomes at a particular gene locus  Homozygous = identical alleles  Heterozygous = different alleles

9. Mendelian Inheritance 9 Law of dominance: Opposed traits, only one shows up Law of segregation: Offspring inherits one of the two alleles Law of independent assortment: Which one allele out of the two - random

10. Mendelian Inheritance 10 Punnett Square Table listing all possible genotypes resulting from a cross  All possible sperm genotypes are lined up on one side  All possible egg genotypes are lined up on the other side  Every possible zygote genotypes are placed within the squares

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14. 14 One-Trait Inheritance Mendel performed cross-breeding experiments  Used “true-breeding” (homozygous) plants  Chose varieties that differed in only one trait (monohybrid cross)  Performed reciprocal crosses ­Parental generation = P ­First filial generation offspring = F 1 ­Second filial generation offspring = F 2  Formulated the Law of Segregation

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16. Mendelian Inheritance 16 Monohybrid Testcross Individuals with recessive phenotype always have the homozygous recessive genotype However, Individuals with dominant phenotype have indeterminate genotype  May be homozygous dominant, or  Heterozygous Test cross determines genotype of individual having dominant phenotype

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20. Mendelian Inheritance 20 Two-Trait Inheritance Dihybrid cross uses true-breeding plants differing in two traits  Observed phenotypes among F 2 plants  Formulated Law of Independent Assortment ­The pair of factors for one trait segregate independently of the factors for other traits ­All possible combinations of factors can occur in the gametes

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25. Mendelian Inheritance 25 Human Genetic Disorders Autosome - Any chromosome other than a sex chromosome Genetic disorders caused by genes on autosomes are called autosomal disorders  Some genetic disorders are autosomal dominant ­An individual with AA has the disorder ­An individual with Aa has the disorder ­An individual with aa does NOT have disorder  Other genetic disorders are autosomal recessive ­An individual with AA does NOT have disorder ­An individual with Aa does NOT have disorder, but is a carrier ­An individual with aa DOES have the disorder

26. Mendelian Inheritance 26 Autosomal Dominant Disorders Neurofibromatosis  Tan or dark spots develop on skin and darken  Small, benign tumors may arise from fibrous nerve coverings Huntington Disease  Neurological disorder  Progressive degeneration of brain cells ­Severe muscle spasms ­Personality disorders

27. Mendelian Inheritance 27 Figure 11.12

28. Mendelian Inheritance 28 Figure 11.13

29. Mendelian Inheritance 29 Autosomal Recessive Disorders Tay-Sachs Disease  Progressive deterioration of psychomotor functions Cystic Fibrosis  Mucus in bronchial tubes and pancreatic ducts is particularly thick and viscous Phenylketonuria (PKU)  Lack enzyme for normal metabolism of phenylalanine

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32. Mendelian Inheritance 32 Incomplete Dominance Heterozygote has phenotype intermediate between that of either homozygote  Homozygous red has red phenotype  Homozygous white has white phenotype  Heterozygote has pink (intermediate) phenotype Phenotype reveals genotype without test cross

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34. Mendelian Inheritance 34 Multiple Allelic Traits Some traits controlled by multiple alleles The gene exists in several allelic forms (but each individual only has two) ABO blood types The alleles:  I A = A antigen on red cells, anti-B antibody in plasma  I B = B antigen on red cells, anti-AB antibody in plasma  I = Neither A nor B antigens, both antibodies Phenotype (Blood Type) Genotype A (actually AA or AO) I A I A or I A i B (actually BB or BO) I B I B or I B i AB IAIBIAIBIAIBIAIB O (actually OO) ii

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41. Mendelian Inheritance 41 George Cecile Wayne Marge Colleen Willy Todd Jack Leah

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