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Announcements. Discussion sections meet next week (T, W, TH) -check the web page for the room (some have changed) HW1 is due Monday in lecture (know who your TA is) Any questions about logistics??. Review of basic Mendelian inheritance.

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  1. Announcements • Discussion sections meet next week (T, W, TH) -check the web page for the room (some have changed) • HW1 is due Monday in lecture (know who your TA is) • Any questions about logistics??

  2. Review of basic Mendelian inheritance • Given that I do not have a cleft chin, which trait is dominant? 2. What is Caleb’s genotype? 3. What information would we need to calculate the probability that the new baby has a cleft chin? Scott Miller Caleb Fishman Miller cleft chins

  3. Review of basic Mendelian inheritance • Given that I do not have a cleft chin, which trait is dominant? This is a bit of a trick question. It is most likely (and true) that cleft is dominant, but from this information you can’t be totally sure. 2. What is Caleb’s genotype? Cc, if cleft allele is C. 3. What information would we need to calculate the probability that the new baby has a cleft chin? What is Scott’s genotype?? How would we figure that out?

  4. Review of basic Mendelian inheritance Assuming that Scott is a heterozygote and cleft is dominant, what is the probability that the new baby will have a cleft chin? Use a Punnett square or simple math...

  5. Learning Goals • Understand Mendel’s 3rd principle • Independent assortment • Use Punnett square and forked-line diagram to predict the inheritance of trait combinations • Understand a test cross

  6. TRAIT VARIANTS White Flower color Purple Terminal Flower position Axial Green Yellow Seed color Seed shape Round Wrinkled Constricted Inflated Pod shape Pod color Green Yellow Tall Dwarf Height

  7. Experimental Protocol (1) Develop parental lines (P) by self-breeding individuals until they are true breeding. (2) Create first-generation progeny (F1) by mating parental lines with alternative phenotypes (e.g., tall x dwarf). (3) Create second-generation progeny (F2) by self-fertilizing F1’s.

  8. F1 generation 25% TT 50% Tt 25% tt F2 generation PHENOTYPE GENOTYPE TT tt P generation Cross-fertilization 100% Tt (tall) 100% tall progeny (hybrids) Self-fertilization (dwarf) (tall) 25% dwarf 75% tall

  9. Mendel’s Principles, so far • Dominance: In a heterozygote, one allele may conceal another. • Segregation: In a heterozygote, two different alleles segregate from each other with equal probability during the formation of gametes. What happens if we consider two traits simultaneously?

  10. TRAIT VARIANTS White Flower color Purple Terminal Flower position Axial Green Yellow Seed color Seed shape Round Wrinkled Constricted Inflated Pod shape Pod color Green Yellow Tall Dwarf Height

  11. R r Rr RR R Round Round Rr rr r Round Wrinkled 3 round : 1 wrinkled

  12. Y y YY Yy Y Yellow Yellow Yy yy y Yellow Green 3 yellow : 1 green

  13. Yellow X Green YY yy Yellow (Yy) Yellow (YY,Yy) 6,022 Green (yy) 2,000 Round X Wrinkled RR rr Round (Rr) Round (RR, Rr) 5,474 Wrinkled (rr) 1,850

  14. Dihybrid cross - seed color and seed texture yyrr YYRR YR yr F1 hybrid seed YyRr gametes? ??? 2 possiblities: complete linkage or independent assortment

  15. round, yellow wrinkled, green RRYY rryy round, yellow RrYy RY ry Gametes Complete linkage: only parental combinations

  16. round, yellow wrinkled, green RRYY rryy round, yellow RrYy RY Ry rY ry Gametes Independent assortment: all combinations possible

  17. Fork Diagram RY 25% Y R R y Ry 25% RrYy rY 25% Y r r y ry 25%

  18. Independent assortment predictions: Dihybrid F2 phenotypes RrYy RrYy x RRYY RRYy RrYY RrYy 9 round, yellow 3 round, green 3 wrinkled, yellow 1 wrinkled, green RRYy RRyy RrYy Rryy RrYY RrYy rrYy rrYY RrYy Rryy rrYy rryy

  19. Mendel’s Data round, yellow wrinkled, green RRYY rryy round, yellow RrYy (self-fertilize) round, yellow wrinkled, yellow round, green green, wrinkled 315 101 108 32 9:3:3:1

  20. Mendel’s Principles • Dominance: In a heterozygote, one allele may conceal another. • Segregation: In a heterozygote, two different alleles segregate from each other during the formation of gametes. • Independent Assortment: The alleles of different genes (or loci) segregate (or assort) independently of each other.

  21. The forked-line method can be used to predict the outcome of an intercross involving three independently assorting genes in peas. TtYyRr x TtYyRr

  22. Use of a test cross Tall Dwarf TT or Tttt

  23. TT or Tt How would you determine if the genotype of this phenotypically tall plant is TT or Tt?

  24. Test cross TT or Tt X tt Tall (Tt) or dwarf (tt) 100% tall (Tt) 50% 50%

  25. Dihybrid test cross ttyy x TtYy TY Ty tY ty TtYy Ttyy ttYy ttyy ty Dwarf, yellow Dwarf, green Tall, yellow Tall, green 25% 25% 25% 25%

  26. Mendelian laws of segregation: mechanism 1: Alleles at a single gene segregate into the gametes at random(1:1 ratio) 2: Alleles at unlinked genes assort independently, so all combinations are equally likely. Both of these laws result from how homologous chromosomes line up in metaphase of Meiosis I.

  27. Why is independent assortment important??

  28. Why is independent assortment important?? How many chromosomally unique gametes can one person make? LOTS!!!!

  29. Next: Video clip for HW 1 ? ?

  30. Independent assortment of chromosomes A A’ A A’ Meiosis I metaphase B B’ B B’ Meiosis II metaphase A’B AB’ A A’ B’ B gametes AB A’B’ A’B AB’ parental

  31. Independent assortment of chromosomes A A’ A A’ Meiosis I metaphase B B’ B B’ Meiosis II metaphase A’B AB’ A A’ B’ B gametes AB A’B’ A’B AB’ nonparental parental

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