By: Mr Knox Purpose History of Inheritance Who was Gregor Mendel? What did he do? Mendel’s Laws of Inheritance Compare to Modern Genetics Simple Dominance Punnett Squares Chapter 8 Heredity History of Inheritance During Mendel’s era 1822-1884 Blending Theory Inherited traits came from a blend of both Parents. Long hair + short hair = medium hair. The nature of these factors of inheritance were not known,... until Mendel. Gregor Mendel Austrian Monk- mathematician Father of Genetics Worked mainly with Pea Plants Worked for 6-7 years! What Did Mendel Do? Worked with the Pea Plant. Pisum Pea Plant Self Pollinates, has closed reproductive system. Let Self Pollinate to make Pure Lines for a trait. Chapter 8 Mendel’s Studies of Traits Mendel’s Breeding Experiments . What did Mendel Do? Mated plants with known traits Evaluated results, based on math, came up with Laws of Inheritance. Mendelian Traits- (Genes) Fig. in Textbook Trait: Dominant Recessive Expression: Expression 1. Form of ripe seed Smooth Wrinkle 2. Color of seed albumen Yellow Green 3. Color of seed coat Grey White 4. Form of ripe pods Inflated Constricted 5. Color of unripe pods Green Yellow 6. Position of flowers Axial Terminal 7. Length of stem Tall Dwarf Definitions Traits = Genes, form of gene called allele 2 Traits/genes, one from male and one from female needed for gene expression. For pea color gene G=dominant, g = recessive G and g are alleles for Pea color gene. Dominant- only needs 1 of the 2 genes for the characteristic to be expressed. GG or Gg Recessive- “hidden trait” in which both genes must be the same form to be expressed. gg Chapter Allele Comparing Dominant and Chapter Recessive Traits Definitions Genotype- actual genetic make up of individual- GG- homozygous dominant- both genes are G. Gg- heterozygous - two different genes or alleles. gg- homozygous recessive- both alleles are g. Definitions Phenotype- what the offspring appears to be. GG, Gg - are both YELLOW gg- is green Genotype will determine your phenotype Sample Experiment Mendel bred pure lines for a trait, example YELLOW PEAS and green peas. YELLOW = GG, green = gg, pure lines P1 x P1 or YELLOW x green P = parents F1 = first filial or “family” = offspring (kids) F1 are called hybrids, results of crossing or mating of two different parents. All F1 offspring were YELLOW GG- Meiosis- (genes on chromosomes) G G g gg Gg Gg g Gg Gg Punnet’s Square The Punnett’s Square below explains simple dominance GG x gg= all YELLOW Yellow is dominant to green G G G and g are egg and sperm, from Meiosis g Gg Gg Gg are zygotes or g Gg Gg offspring from fertilization F1 x F1 or YELLOW x YELLOW Mendel then crossed F1 with F1 Ratio of offspring or F2 came out 3 to 1, YELLOW to green F1 x F1 or YELLOW x YELLOW Mendel crossed two YELLOW peas Some offspring were green. G g This showed that G GG Gg some traits were g Gg gg hidden or recessive Three Steps of Mendel’s Experiments 8 Chapter Punnett Square Shows the PROBABLE outcome/ratio not the actual! Ratios for P x P The phenotype ratio of crossing G G pure YELLOW GG g Gg Gg with pure green gg g Gg Gg would be All Yellow or 4 to 0 Genotype ratio is also all Gg Ratios for F1 x F1 Genotype ratio would be G g 1 GG G GG Gg 2 Gg 1 gg g Gg gg 1:2:1 Phenotype ratios for crossing Gg x Gg are 3 YELLOW : 1 green Chapter 8 Mendel’s Crosses and Results What are the possible parents genotype or genetic make up? Genotype and Phenotype Genotype determines what you “look” like or your Phenotype. Based on what you look like, you may not know what your actual genetic make up is. A seed that is YELLOW could be either GG or Gg. However a green recessive will be gg Testcross If known phenotype YELLOW but unknown genotype then you mate with a recessive for trait- gg. Someone tell me how you can tell the genotype is GG or Gg???? ? Offspring will be exhibit recessive trait if Gg. Mendel’s Laws of Inheritance Keep in mind, Mendel did not know of Chromosomes or Genes Dominant or Recessive Meiosis Laws he derived were based on MATH and probabilities Laws of Inheritance Law of Dominance- one trait is “seen” while the other is “hidden” Laws of Inheritance Law of Segregation (meiosis)- parents transmit “factors” (genes) to offspring in pairs, one from each parent. Chapter 8 Mendel’s Factors Laws of Inheritance Law of Independent Assortment- each trait is independent from each other, meaning pea color did not effect tallness, etc... Testing for Genotype In order to determine the actual genetic make up of the Parent, the offspring are examined after the Parents are crossed. The ratio of offspring can determine the genotype of the Parent. Mendel used this method.
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