Intro to Mendelian Genetics

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)