Genetics according to Mendel and Morgan, a reminder:

1. ♂ = ♀ ♂ ♀ Genetics according to Mendel and Morgan, a reminder: Our chromosomes: A: autosome A A A A ♂ ♀ X X Y X X ou Y: sex-associated chromosomes

2. For the meiosis of Autosomes: + m [+] A1 A2 ♂ [+] ♀ A1 + / A1 + A1 + / A2 m + A1 + = wild-type, dominant ; m = mutation, recessive ♀, ♂ [+] [+] ♀, ♂ A2 m / A2 m A1 + / A2 m A2 m [mutant] ♀, ♂ [+] ♀, ♂ ♀ = ♂ : ¾ [+], ¼ [mutant]

3. X1 Y ♂ ♀ X1 X1/ X1 X1/ Y X2 X1/ X2 X2/ Y A similar – but not identical - situation holds for sex chromosomes : + [+] [+] + ♀ [+] ♂ [+] m [m] ♂ ♀ [+] ¾ [+], ¼ [mutant]but! ♀  ♂

4. Color perception and photoreceptors: Red green and blue Daltonism, or Red-Green color blindness: a syndrome associated with the X chromosome X A

5. Color perception and photoreceptors: Red green and blue A A Y X

6. Sex Chromosomes vs. Autosomes [+] X1 A YA ♂ [+] ♀ X1 A [+] X1/ X1; A/A X1/ Y; A/A [+] X2 A [+] [Red-green Color Blind] X2/ Y; A/A X1/ X2; A/A ♂ ♀ Red

7. Color perception and photoreceptors: Red green and blue Woman normal Woman carrier Man normal Man Color blind Y Y X X X X X X A A A A A A A A R+V+B+ R+V+B+ R+V+B+ V+B+

8. Color perception and photoreceptors: Red green and blue Where do nearly identical DNAs for Red and Green come from? X A

9. Common ancestor Duplication then Divergence * * * * ** *

10. Color perception and photoreceptors: Red green and blue Recent duplication Divergence

11. Origin of photoreceptors: Blue Green Red More ancient duplication divergence duplication divergence

12. High frequency of Daltonism. Where do so many mutations come from??? X A

13. Normal pairing Inappropriate pairing X Recombination by error New mutations One example: illegitimate recombination … And the loss of normale function.

14. Giant chromosomes of Drosophila in the nucleus after spreading

15. Traditional karyotype for a human cell (e.g. amniocentesis) 2 copies = normal Trisomy for chromosome 21 with associated defects (mongolism)

16. Fluorescent In Situ hybridization: FISH Fluorescent DNAs, different colors for different chromosomes

17. Karyotype by FISH Fluorescent In Situ hybridization T+ Chr21 =>Trisomy / Chromosome 21

18. E.g. Burkitt’s Lymphoma

19. Regulatory DNA Sequences Coding DNA Sequences A normal gene : mRNA Where? When? How much? protein function

20. Strong immune expression General expression Strong immune expression General expression IgH protein C-myc oncogene IgH protein C-myc oncogene FISH applied to disease diagnosis One normal gene : Breakage/repair with error Another normal gene :

21. General expression Strong immune expression C-myc oncogene Strong immune expression c-myc oncogene Fluorescent In Situ hybridization: FISH Normal : IgH protein Fluorescent DNA-1 Abnormal : Also normal : Fluorescent DNA-2

23. And what about the lab?

24. The nematode C. elegans as a laboratory model Hermaphrodite (XX) + ~1 mm (XO) Eating E. coli

25. Screening for mutants mutagen New, recessive mutation m + + m m + + +/ + +/ m +/ + +/ m m +/ m m/m

26. m/m m/m m/m m/m Inbreeding in the lab is helpful m + m m + m +/ + +/ m m m +/ m m/m A new mutant line

27. A A a a A A a a A a 2n 4n Meiosis: one mother cell becomes four gametes 2 x ‘2n’ 4 x 1n (gametes) Here, we only look at one pair of chromosomes among several…

28. A a A A A a a A a a Linkage of DNA sequences on the same chromosome (Mendel I); Independent transmission of different chromosomes (Mendel II) 1/4 1/2 A 1/4 a OU 1/4 2n 1/4 1/2 4n 4 x 1n (gametes) A/a = forms of a gene 2 x ‘2n’ = transposable element insertions

29. Additional variation from physical exchanges (recombination)

30. A a A A a A A a a a Recombination generates still more diversity 4xRecombinant 4xParental f < 0.5 <1/4 A x <1/4 a <1/4 2n 4n <1/4 A/a = forms of a gene = transposable element insertions 4 x 1n (gametes)

31. XX 11 22 33 44 55 (XX) Bristol X (XO) Autosomes Sex chromosome sma-5 dpy-6 lin-14 X

32. Isolating mutants that affect vulval development: the bag of worms screen + Egg-laying Vulva: muscles, nerves, skin… lin-14 Defective vulva = [Bag of worms] Defective vulva

33. 11 22 33 44 55 (XX) Bristol (XO) Autosomes Sex chromosome lin-14- lin-14- lin-14 - lin-14- (but otherwise +) lin-14+ (XX) lin-14+ Bergerac lin-14+ lin-14 + (XO) (& otherwise +) Tc1 elements

34. lin-14 - lin-14 - Bris Bris lin-14- lin-14- lin-14+ lin-14+ (effect female-specific) X lin-14 + Berg Meiosis + recombination lin-14- [lin-14+] lin-14+ « Backcross » N°1 X

35. lin-14 - lin-14 - Bris Bris lin-14- lin-14- Serial dilutions, genetic-style Meiosis + recombination lin-14- [lin-14+] x x x x x x x x x x x lin-14+ « Backcross » N°1 X lin-14- [lin-14+] lin-14+ « Backcross » N°2 X

36. Meiosis + recombination Bris Bris lin-14 - lin-14 - lin-14- lin-14- lin-14- [lin-14+] lin-14+ « Backcross » N°2 X lin-14- [lin-14+] lin-14+ « Backcross » N°3 X

37. Dilution = 29 « Backcross » N°9 lin-14- [lin-14+] lin-14+ Self-fertilize, select normal hermaphrodites, giving only normal offspring => lin-14+ / lin-14+, pure homozygous stock. Associating the repeated elements closest tolin-14+

38. lin-14+ lin-14+ sma-5+ dpy-6+ lin-14+ X Tc1 Tc2 lin-14+ The approximate location is identified by the Tc1 repeats. Candidate genes in the known genome sequence can be tested.

39. Genetic analysis of Aniridia, a rare eye syndrome caused by a Dominant mutation +/+ An/+ Iris reduced => pupil open Dominant ≥ 1 base pair changed out of 3 billion (3x109)

40. Aniridia (human) : a dominant autosomal syndrome caused by mutation of a single gene, Pax6 Pax-6 Autosomal and dominant: An/+ x +/+ ↓ ½ [An], ½ [+] ♀ = ♂

41. + + + + + + Δ(deletion) a (Faux-sens) Pax6 Pax6 Pax6 Pax6 Pax6 Pax6 * Δ a Pax6 / / Pax6 pf = [Aniridia] = pf => Aniridia results from dominant loss-of-function mutations of Pax6 (haploinsufficient: not enough active protein)

42. Small eye, a mouse version of Aniridia + Sey/+ Sey/+ Small eye (Sey) : Small eye, reduced iris, cranio-facial defects (as for Aniridia) Origin: dominant, haploinsufficient mutations of the mouse Pax6 gene

43. Genotype/phenotype for Sey + [Sey] Sey A1 A2 ♂ [Sey] ♀ A1 + / A1 + A1 + / A2 Sey + A1 ♀, ♂ [+] [Sey] ♀, ♂ A1 + / A2 Sey ? A2 Sey [Sey] ♀, ♂ Expected : ♀, ♂ equivalent: 1/4 [+], 2/4 [Sey], ¼ [?]

44. + [Sey] Sey A1 A2 ♂ [Sey] ♀ A1 + / A1 + A1 + / A2 Sey + A1 ♀, ♂ [+] [Sey] ♀, ♂ A2Sey / A2Sey A2 A1 + / A2 Sey Sey [dead] ♀, ♂ [Sey] ♀, ♂ Genotype/phenotype for Sey Observed : living ♀ = ♂ : 1/3 [+], 2/3 [Sey] ( and ¼ Sey/Sey [dead] )

45. Dead how? As eyeless embryos… => Pax6 / Sey required for normal eye differentiation +/+ Sey/Sey

46. Normal eye development follows a genetic program Localised expression of Pax6 (mRNA) and requires Pax6+

47. Normal Pax6 expression is necessary for eye development Localised geneexpression = normal No expression = absence of function

48. + The Drosophila eyeless (ey) gene encodes dPax6 - ey Pax6 is necessary for normal Drosophila eye development - as in man and mouse -

49. gf dPax6 -/- mPax6 -/- dPax6 Human, mouse + + + Drosophila

50. humain Very different eyes with a common origin? calamar mouche