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Introduction to Mendelian Genetics

Chapter 11.1-11.3. Introduction to Mendelian Genetics. 11-1 Work of Gregor Mendel. 11-2 Probability & Punnett Squares. Introduction to Genetics. 11-3 Exceptions to Mendelian Genetics. 11-3 Exploring Mendelian Genetics. Genetics Vocabulary.

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Introduction to Mendelian Genetics

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  1. Chapter 11.1-11.3 Introduction to Mendelian Genetics

  2. 11-1 Work of Gregor Mendel 11-2 Probability & Punnett Squares Introduction to Genetics 11-3 Exceptions to Mendelian Genetics 11-3 Exploring Mendelian Genetics

  3. Genetics Vocabulary • Genetics – the study of passing on of genes from parent to offspring • Gene = part of DNA coding for trait • Trait = Characteristic • Seed shape, seed color, plant height • Allele = alternate forms of a gene • Eye color: blue, green, brown, hazel, etc.

  4. Gregor Mendel & Pea Plants • 7 traits each with 2 contrasting alleles • seed shape, seed color, plant height, pod color, pod shape, seed coat color, flower position • Self-pollination (also known as true-breeding) vs. Cross-pollination (also known as selective breeding)

  5. Mendel controlled the fertilization of his pea plants by removing the male parts, or stamens. He then fertilized the female part, or pistil, with pollen from a different pea plant. Mendel’s 1st experiment

  6. Mendel’s 1st Conclusion • Law of Dominance • Dominant allele v. Recessive allele • Capital letter = dominant (ex: tall= T) • Lowercase letter = recessive (ex: small= t) • Each individual has 2 alleles (homologous) • TT =Tall • Tt = Tall • tt = small • Genotype = gene combination (represented by alphabet letters) • Phenotype = Physical appearance (represented by words)

  7. Mendel’s 2nd Experiment • F1 generation x F1 generation • Tall (____) x Tall (____) • 2nd Experiment Results

  8. Mendel’s 2nd Conclusion • Law of segregation • Alleles separate during gamete formation (meiosis) • Homologous chromosomes separate!! (phase?) • Review • Tall (____) x Tall (____) • Phenotype: • 3 tall & 1 short

  9. Genetic Terminology • Genotype: Gene make-up • Alleles inherited • Ex: Height: • Phenotype: Physical appearance • Ex: Height: • TT= • Tt= • tt= • Homozygous = Purebred • Alleles in pairalike • Homozygous Dominant • Ex: Height • Genotype= TT • Phenotype= Tall • Homozygous Recessive • Ex: Height • Genotype= tt • Phenotype= small • Heterozygous = Hybrid • Alleles in pair different • Ex: Height • Genotype= Tt • Phenotype=Tall TT, Tt, tt Tall Tall Short

  10. Predicting Monohybrid Crosses: Height Gametes • Punnett Square = diagram to predict offspring • Larger # offspring closer to expected • Monohybrid cross = cross of one trait • Homozygous Dominant x Homozygous Recessive • Step 1: determine parents • Height TT x tt • Step 2: Put parents on punnett square • Step 3: Predict • Step 4: Genotypic & Phenotypic ratios • Genotypic- 0 TT:4 Tt: 0 tt • Phenotypic- 4 Tall: 0 Short

  11. Punnett Monohybrid Cross: Height • Homozygous Dominant x Heterozygous • Step 1: ID parents • Step 2: add parents to Punnett • Step 3: Predict • Step 4: Genotypic & Phenotypic ratios • Genotypic ratio = ____________ • Phenotypic ratio = ____________ • Homozygous recessive x Heterozygous • Genotypic ratio = _______________ • Phenotypic ratio = ______________

  12. Punnett Monohybrid Cross • Heterozygous x Heterozygous • Genotypic ratio = ____________ • Phenotypic ratio = ____________ • Testcross • Determine unknown genotype of phenotypic dominant trait • Unknown Dominant x recessive • OR • Ratios Ratios

  13. Punnett Dihybrid Crosses • Cross 2 pairs of contrasting traits • Ex: seed texture & seed color at same time • Hom. Round &Yellow x Hom. Wrinkled & Green • Step 1: determine parents • RRYY x rryy • Step 2: determine possible gametes (* independent assortment) • RRYY RY, RY, RY, RY • rryy ry, ry, ry, ry • Step 3: Set-up Punnett Square • Step 4: Predict • Step 5: Phenotypic ratios

  14. Dihybrid Cross Punnett Square Phenotypic Ratios Round Yellow =16 Round Green = 0 Wrinkled Yellow=0 Wrinkled Green=0 Ratio 16:0:0:0

  15. Dihybrid Cross Phenotypic Ratio: Round Yellow= Round Green= Wrinkled Yellow= Wrinkled Green= Ratio: WHY & HOW? Heterozygous x Heterozygous

  16. Mendel’s 3rd Conclusion • Law of independent assortment • Alleles on separate chromosomes separate independently of each other during meiosis • AKA homologous chromosomes separate independently of each other (phase?) • Accounts for genetic variation!! • Review of possible gametes in dihybrid cross • RRYY RY, RY, RY, RY • rryy ry, ry, ry, ry Due to Law of Independent assortment

  17. Mendel Summary • Traits determined by genes & are passed on • Most sexually reproducing adults have 2 copies of each gene (AKA 2 alleles) one from each parent • Law of Dominance vs Recessive • Law of Segregation • Law of Independent Assortment

  18. Artificial Selection • Selective Breeding – known as artificialselection, peopleselect the traits they want to have passed on. • Inbreeding– can cause genetic defects because the DNA is too similar to each other. • Hybridization– A mixof two different traits

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