Mendelian Genetics
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GENETICS Definition Study of how hereditary characteristics (traits) in an individual are transmitted from one generation to the next. Milestones Mendel “Genes and the Rules of Inheritance” Watson & Crick “The Structure of DNA” Human Genome Project “Sequencing DNA & Cataloging Genes” Levels of Genetic Analysis Classical Structure and Behavior of Chromosomes Nature of Genetic Material Molecular Defining DNA Sequences Recombination Gene Manipulation Population Variation of Genetic Makeups Inheritance of Traits Mendelian Genetics Gregor Mendel Contributions Law of Segregation Dominant and Recessive Traits Fig. 23.1 Mendel's Studies of Inheritance Hypothesis Pea plants inherit two “units of information” (genes) for a trait, one from each parent Monohybrid Experiment Parental Monohybrid Cross Design True breeding strains of purple (P) flowered peas were crossed with true strains of white(p) flowered peas. * True breeding = homozygous PP X pp P P x p p FORMATION OF GAMETES PP x pp P P p p F1 Generation Punnett Square Analysis PP X pp P p p P F1 Generation Punnett Square Analysis PP X pp P P p Pp Pp p Pp Pp F1 Generation Punnett Square Analysis Genotype: Pp Phenotype: Purple F2 Generation Punnett Square Analysis F1 Generation Monohybrid Cross Design Crossing of two F1 generation plants Pp X Pp P P p x p F2 Generation Punnett Square Analysis P p P PP Pp p Pp pp F2 Generation Punnett Square Analysis Genotypes: PP, Pp, pp Phenotypes: Purple White Genotypic Ratio 1 (25%): Homozygous Dominant 2 (50%): Heterozygous 1 (25%): homozygous recessive Phenotypic Ratio 3 (75%): Purple 1 (25%): White MENDELIAN GENETICS Conclusions 1) Each trait (gene) has two forms (alleles) which segregate at the formation of gametes 2) One allele which is dominant masks the appearance of the other allele which is recessive. Dihybrid Experiment Parental Dihybrid Cross Design True breeding strains of peas that were homozygous for red (R) flower color and green (G) seed pod color were crossed with true breeding strains that were homozygous for white (r) flower color and yellow (g) seed pod color. R R r G G r g x g R R R INDEPENDENT ASSORTMENT RRxRR GGxGG RRxRR GGxGG RRGG RG RRGG RG RG RG INDEPENDENT ASSORTMENT rrxrr ggxgg rrxrr ggxgg rrgg rg rrgg rg rg rg F1 Generation Punnett Square Analysis RRGG X rrgg rg RG RrGg RG RG RG rg rg RrGg RrGg rg F2 Generation Punnett Square Analysis F1 Generation Dihybrid Cross Design Crossing two F1 generation plants RrGg X RrGg Possible Gametes RG, Rg, rG, rg R r Rr G g r g G x g INDEPENDENT ASSORTMENT R r R r g G or G g INDEPENDENT ASSORTMENT RRxrr GGxgg RRxrr GGxgg RRGG RG rrgg RG rg rg INDEPENDENT ASSORTMENT RRxrr GGxgg RRxrr ggxGG RRgg Rg rrGG Rg rG rG RG RG Rg Rg rG rg RRGG RRGg RrGG RrGg RRGg RRgg RrGg Rrgg rG RrGG RrGg rrGG rrGg rg RrGg rrGg rrgg Rrgg F2 Generation Punnett Square Analysis Genotypes RRGG RRGg RrGg RrGG Rrgg RRgg rrGG rrgg Phenotypes Red Flowers, Green Pods Red Flowers, yellow pods white Flowers, Green pods white flowers, yellow pods Genotypic Ratios 1: RRGG 2: RRGg 4: RrGg 2: RrGG 2: Rrgg 1: RRgg 1: rrGG 1: rrgg 2: rrGg Phenotypic Ratios 9: Red, Green 3: Red, yellow 3: white, Green 1: white, yellow DYHIBRID CROSS Conclusion Independent Assortment 1)As meiosis ends, genes on pairs of homologous chromosomes have been sorted out for distribution into one gamete or another, independently of gene pairs on other chromosomes. 2) Independent Assortment leads to genetic diversity in populations.
