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Genetics

Genetics. How are traits passed from parents to offspring?. Chapter Introduction. Gregor Mendel. Studied heredity – the passing of traits from parents to offspring. Gregor Mendel is known as the father of genetics —the study of how traits are passed from parents to offspring. Grow quickly

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Genetics

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  1. Genetics

  2. How are traits passed from parents to offspring? Chapter Introduction

  3. Gregor Mendel • Studied heredity– the passing of traits from parents to offspring. • Gregor Mendel is known as the father of genetics—the study of how traits are passed from parents to offspring.

  4. Grow quickly • Come in many varieties • Mendel could control pollination Mendel studied genetics by doing controlled breeding experiments with pea plants… Why peas?

  5. There are two types of pollination: Self pollination Cross pollination Plant Pollination

  6. Self-Pollination Lesson 1

  7. Cross-Pollination Lesson 1

  8. Used plants that he knew were true-breeding • True breeding—when a plant self-pollinates it will always produce more plants with the same traits; (is homozygous) (a.k.a. purebred) = X Mendel’s Experiments

  9. Mendel crossed (mated) a true-breeding purple flowered pea plant with a true-breeding white flowered pea plant • All of the offspring had purple flowers! = X (Offspring) (Parents) Mendel’s Experiments continued…

  10. (Transparency demo) • Dominant—the trait that appears if two traits are mixed (capital letter) • Recessive—trait that is hidden if 2 traits are mixed (lowercase) • Purple flowers are dominant over white flowers What happened to the white flowers?

  11. Mendel’s Results (cont.) hybrid Science Use the offspring of two animals or plants with different forms of the same trait Common Use having two types of components that perform the same function, such as a vehicle powered by both a gas engine and an electric motor Lesson 1

  12. Mendel also cross-pollinated hybrid plants. 75% = X 25% Parents Offspring Mendel’s Experiments continued…

  13. The trait for white flowers showed up again! • He observed that offspring of hybrid crosses always showed traits in a 3:1 ratio. 75% 25% Mendel’s Experiments continued…

  14. Mendel concluded that two factors, one from each sperm and one from each egg, control each inherited trait. Mendel’s Experiments continued…

  15. The factors that Mendel talked about are called genes • A gene is a section on a chromosome that has genetic information for one trait. Gene

  16. One trait/gene may have a few different varieties • Example: hair color • The different forms of a gene are called alleles brown blonde red Genes continued…

  17. Lesson 2

  18. The GENetic code (or combination of alleles) of an organism is called its GENotype • Shown as 2 letters per trait • Example: someone with brown hair might be BB One allele from mom One allele from dad Genotype

  19. What Controls Traits(cont.) • When the two alleles of a gene are the same, the genotype is true breeding, or homozygous. • If the two alleles of a gene are different, the genotype is hybrid, or heterozygous. Lesson 2

  20. B= brown hair b=blonde hair • BB • Bb • bb Brown Hair Homozygous (true-breeding) Brown Hair Heterozygous (hybrid) Blonde Hair Homozygous (true-breeding) Check this out…

  21. P = purple flowers in pea plants, p= white flowers in pea plants • PP • Pp • pp Purple Purple White Lets see how quick you are….

  22. Choice of letter code is up to you… • Usually the first letter of the trait • Capital letter means the trait is dominant • Lower case means it is recessive What letters do you use?

  23. Phenotype • The PHenotype is the PHysical appearance of the organism • Example: brown hair, purple flowers, blue eyes Lesson 2

  24. Bb x Bb B b B BB Bb Bb bb b A Punnett Squareis a model used to predict possible genotypes and phenotypes of offspring.

  25. Bb x Bb • Probability of Brown: 3 out of 4; 75% • Probability of blue: 1 out of 4; 25% B b BB Bb B brown brown Bb bb b brown blue Probability- the mathematical chance an event will occur

  26. Bb x Bb • Probability of Brown: 3 out of 4; 75% • Probability of blue: 1 out of 4; 25% • Phenotypic Ratio is 3:1 (Brown:blue) B b BB Bb B brown brown Bb bb b brown blue Phenotypic Ratio

  27. Bb bb Bb x Bb • Probability of BB: 1 out of 4; 25% • Probability of Bb: 2out of 4; 50% • Probability of bb: 1 out of 4; 25% • Genotypic Ratio is 1:2:1 (BB:Bb:bb) BB Bb B brown brown Bb bb b brown blue Genotypic Ratio

  28. Modeling Inheritance (cont.) A pedigree shows phenotypes of genetically related family members. Lesson 2

  29. Complex Patterns of Inheritance • Sometimes traits appear to be blends of alleles. • Alleles show incomplete dominance when the offspring’s phenotype is a blend of the parents’ phenotypes. Lesson 2

  30. Red, white and pink flowers • R=red • r=white Snapdragons

  31. How do you get pink flowers? • RR • Rr • rr Red Pink White Snapdragons continued…

  32. Mixing of two traits (blending) • One dominant allele is only “half-strong” • Red + white = pink R=red r=white Incomplete dominance

  33. Complex Patterns of Inheritance • Codominance occurs when both alleles can be observed in a phenotype. Lesson 2

  34. Fur can be red or white • Mixing the two gives roan fur Cattle

  35. Both alleles are expressed at the same time in the phenotype • Red fur + white fur = roan fur (red and white mixed) R=red r=white Codominance

  36. Incomplete & Codominance Websites

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