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Intro to Mendelian Genetics

Intro to Mendelian Genetics. 1.28.13. What is genetics?. What is genetics?. The science of heredity. What is genetics?. The science of heredity How traits are passed to offspring. What is genetics?. The science of heredity How traits are passed to offspring

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Intro to Mendelian Genetics

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  1. Intro to Mendelian Genetics 1.28.13

  2. What is genetics?

  3. What is genetics? • The science of heredity

  4. What is genetics? • The science of heredity • How traits are passed to offspring

  5. What is genetics? • The science of heredity • How traits are passed to offspring • Gene – A section of DNA that codes for a specific protein • Gene – The unit of heredity

  6. Gregor Mendel • Born in Czech Republic, settled in Austria • In 1842, entered monastery at age of 21, tended to a garden of peas

  7. Gregor Mendel • In 1851 he went to the U. of Vienna to study science and statistics • Returned to monastery to teach high school and study heredity through his peas. (OMG, this is like sooooo exciting! I can’t wait to hear what happens next. Seriously, I’m about to pea my pants!)

  8. Current thoughts in 1850 • Blended inheritance • Offspring are intermediate in appearance

  9. Current thoughts in 1850 • Blended inheritance • Offspring are intermediate in appearance • Ex: skin tone in humans

  10. Current thoughts in 1850 • Blended inheritance • Offspring are intermediate in appearance • Ex: skin tone in humans • Ink in water • Combined • Inseparable

  11. Current thoughts in 1850 • Blended inheritance – (Incorrect) • Offspring are intermediate in appearance • Ex: skin tone in humans • Ink in water • Combined • Inseparable

  12. Used peas to study inheritance • Why peas?

  13. Used peas to study inheritance • Each plant has various traits to study • Cheap • Simple to grow • Seeds easily stored for later study • Short generation time • Self-pollinators (flowers have male and female parts) • Cloned flowers can serve as control group

  14. Statistics was the key! • Used math to explain living systems (one of the first to do so) • Published his work in 1866, but mostly ignored because he didn’t know the mechanism of heredity (DNA)

  15. Mendel’s 1st Experiment • Studied 7 characteristics with two traits each • Plant height, flower color, etc.

  16. Mendel’s 1st Experiment • Studied 7 characteristics with two traits each • Plant height, flower color, etc. • Focus on plant height: • Tall or short:

  17. Mendel’s 1st Experiment • Studied 7 characteristics with two traits each • Plant height, flower color, etc. • Focus on plant height: • Tall or short: T or

  18. Mendel’s 1st Experiment • Studied 7 characteristics with two traits each • Plant height, flower color, etc. • Focus on plant height: • Tall or short: T or t

  19. Mendel’s 1st Experiment • Studied 7 characteristics with two traits each • Plant height, flower color, etc. • Focus on plant height: • Tall or short: T or t • All studied traits were heritable, not environmental • Used purebreds (clones) achieved through many generations of self-pollination

  20. Mendel’s 1st Experiment • Crossed a purebred tall with a purebred short • Paternal: T xt • Filial (F1): ??

  21. Mendel’s 1st Experiment • Crossed a purebred tall with a purebred short • Paternal: T xt • Filial (F1): 100% tall (T) • Same result with all 7 characteristics • Trait that showed up in F1 generation = dominant • Disappearing trait = recessive

  22. Mendel’s 1st Experiment • Where did the recessive trait go?

  23. Mendel’s 1st Experiment • Where did the recessive trait go? • To find out, he self-pollinated the F1 plants • F1: T x T

  24. Mendel’s 1st Experiment • Where did the recessive trait go? • To find out, he self-pollinated the F1 plants • F1: T x T • F2: 75% T, 25% t

  25. Law of segregation • Law of segregation : Traits are discrete units that occur in pairs and retain their integrity

  26. Law of segregation • Law of segregation : Traits are discrete units that occur in pairs and retain their integrity • Characteristics are now called genes (one or more genes lead to the appearance of a certain characteristic)

  27. Mendelian Genetics Continued… • The location (address) of a gene on a chromosome is called the locus • Genes have alternate versions called alleles • ex: locus for flower color

  28. Genotype: The collection of alleles in an individual • Represented by letters

  29. Genotype: The collection of alleles in an individual • Represented by letters • P: TT xtt(T = dominant allele –> only one needed for expression) • F1:

  30. Phenotype:

  31. Phenotype: Physical expression of genotype + environment • Represented by

  32. Phenotype: Physical expression of genotype + environment • Represented by descriptive words • F2 : Tt x Tt Genotypes: Phenotypes:

  33. Genotype terminology • TT = Homozygous dominant or purebred dominant • Tt = • tt =

  34. Genotype terminology • TT = Homozygous dominant or purebred dominant • Tt = Heterozygous dominant or hybrid • tt = Homozygous recessive or purebred recessive

  35. How can you tell the difference between a homozygous dominant (DD) and a heterozygous dominant (Dd)?

  36. How can you tell the difference between a homozygous dominant (DD) and a heterozygous dominant (Dd)? • Test Cross: Breed the unknown with a homozygous recessive to bring out any hidden recessive traits

  37. Test Cross: Breed the unknown with a homozygous recessive to bring out any hidden recessive traits

  38. Law #1: Law of segregation • Law #2: Law of independent assortment • Genes located at different loci (locations) on the same chromosome assort (cross-over) independently of each other

  39. Law #1: Law of segregation • Law #2: Law of independent assortment • Genes located at different loci (locations) on the same chromosome assort (cross-over) independently of each other • (Whether one gene crosses over during meiosis has no influence over whether another gene on the same chromosome crosses over)

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