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Unformatted text preview: Transmission of Genes from Generation to Generation
Chapter 3 Brother Mendel Johann Gregor Mendel 18221884 Austrian monk Mendel: Old, yes. Dead, yes, but oh so important
The important points of Mendel's research:
1. 2. 3. 4. Traits are passed on in material units These units come in pairs The units get passed on from generation to generation Pairs separate during gamete formation Mendel's Ideas What do we call the inheritable units now? Replaced the hypothesis of blending. Mmmmm...Peas
Why peas? Identifiable traits Self fertilizing Can be artificially fertilized Short growth period Experimental Design Large sample size One pair of traits at a time Repeated experiments Analyzed his data with probability and statistics Keys to his success were methodical approach and lack of preconceived notion Phenotype and Genotype Phenotype = Genotype = Talking about Genetics Allele = Dominant Allele = Recessive Allele = P1 Smooth x wrinkled Parental (P) Generation
F1 Smooth First Filial (F1) Generation Fig. 3.3 Self-fertilize F1 plants Second Filial (F2) Generation F2 5,474 Smooth x 1,850 wrinkled Total peas in F2: 7,324 Results F1 had only one of two parental traits All crosses were the same Disappearing trait reappeared in 25% of F2 Phenotypic ratio = 3:1 Mendel's Results Fig. 3.4 Law of Segregation Gene pairs separate in gamete Parent passes on only ONE of these Determines probability of getting a Punnett Squares particular offspring letter letter Dominant allele: written as upper case Recessive allele: written as lower case Always use the same letter E.x. A and a for the same trait Punnett Square
Fig. 3.6 Punnet Squares
Aa (female) x Aa (male)
A A a a Allele Combinations Homozygous = Heterozygous = Homozygotes & Heterozygotes
Examples: TT = Phenotype = tt = Phenotype = Tt = Phenotype = Locus = Genes Are Located on Chromosomes Humans have ~30,000 genes 22 autosomes and the X and Y chromosomes Monohybrid vs. Dihybrid Cross Monhybrid cross = Dihibrid cross = Monohybrid Cross
In F2: Fig. 3.7 Phenotypic Ratio = 3:1 Genotypic Ratio = 1:2:1 Dihybrid Cross Fig. 3.8 Results of Dihybrid Cross Phenotypic Ratio = 9:3:3:1 Demonstrates traits are inherited SEPARETLY from each other Dihybrid Cross Fig. 3.9 Combined Probabilities Or, the easy way to do this... Calculate combined probabilities Multiplying fractions...let's practice Independent Assortment Allele pairs separate during sperm/egg formation Alleles are inherited independently from each other Ex: widows peak and dimpled chin Meiosis & Mendel's Results
Fig. 3.10 Fig. 3.10 Multiple Alleles For some genes, more than two alleles ABO Blood type: Three alleles: IA ,IB or i Fig. 3.11 Mendel's Rules don't always apply
Cases where these rules don't seem to apply: Incomplete dominance = Codominance = Incomplete Dominance
Fig. 3.12 Codominance Mendelian Inheritance in Humans Pigmentation Gene and Albinism Fig. 3.14 Two Genes Fig. 3.15 Pedigree Symbols Fig. 3.16 Proband First affected family member who seeks medical attention for a genetic disorder Autosomal Recessive Fig. 3.17 ...
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This note was uploaded on 04/04/2008 for the course BIOL 105C taught by Professor Drake during the Fall '07 term at Saginaw Valley.
- Fall '07