Genetics & The Work of Mendel

1. Genetics&The Work of Mendel

2. Gregor Mendel • Modern genetics began in the mid-1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in peas • used good experimental design • usedmathematicalanalysis • collected data & counted them • excellent example of scientific method

3. Mendel’s work Pollen transferred from white flower to stigma of purple flower • Bred pea plants • cross-pollinate true breeding parents • raised seed & then observed traits • allowed offspring to self-pollinate& observed next generation all purple flowers result self-pollinate ?

4. Mendel collected data for 7 pea traits

5. true-breeding purple-flower peas true-breeding white-flower peas 100% purple-flower peas 1st generation (hybrids) 100% 75% purple-flower peas 25% white-flower peas 3:1 2nd generation Looking closer at Mendel’s work X Parents self-pollinate

6. What did Mendel’s findings mean? • Some traits mask others • purple & white flower colors are separate traits that do not blend • purple x white ≠ light purple • purplemaskedwhite • dominant allele • functional protein • affects characteristic • masks other alleles • recessive allele • no noticeable effect • allele makes a non-functioning protein I’ll speak for both of us! allele producingfunctional protein mutant allele malfunctioningprotein homologouschromosomes

7. X P purple white F1 all purple Genotype vs. phenotype • Difference between how an organism “looks” & its genetics • phenotype • description of an organism’s trait • genotype • description of an organism’s genetic makeup Explain Mendel’s results using …dominant&recessive …phenotype&genotype

8. PP pp x X P purple white F1 all purple Making crosses • Can represent alleles as letters • flower color alleles  P or p • true-breeding purple-flower peas  PP • true-breeding white-flower peas  pp Pp

9. PP 25% male / sperm P p Pp 50% 75% P Pp female / eggs pp p 25% 25% Aaaaah, phenotype & genotypecan have different ratios Punnett squares Pp x Pp 1st generation (hybrids) % genotype % phenotype PP Pp Pp pp 1:2:1 3:1

10. Any Questions??

11. Beyond Mendel’s Lawsof Inheritance

12. Extending Mendelian genetics • Mendel worked with a simple system • peas are genetically simple • most traits are controlled by single gene • each gene has only 2 version • 1 completely dominant (A) • 1 recessive (a) • But its usually not that simple!

13. Incomplete dominance • Hybrids have “in-between” appearance • RR = red flowers • rr = white flowers • Rr = pink flowers • make 50% less color RR WW RW RR Rr rr

14. 100% pink flowers 1st generation (hybrids) 100% 25% red 50% pink 25% white 1:2:1 2nd generation Incomplete dominance X true-breeding red flowers true-breeding white flowers P self-pollinate

15. RR 25% 25% male / sperm R W RW 50% 50% R RW female / eggs WW W 25% 25% Incomplete dominance RW x RW % genotype % phenotype RR RW RW WW 1:2:1 1:2:1

16. Codominance • Equal dominance • human ABOblood groups • 3 version • A, B, i • A& B alleles are codominant • both A& B alleles are dominant over i allele • the genes code for different sugars on the surface of red blood cells • “name tag” of red blood cell

17. Genetics of Blood type

18. Blood donation clotting clotting clotting clotting clotting clotting clotting

19. One gene: many effects • The genes that we have covered so far affect only one trait • But most genes are affect many traits • 1 gene affects more than 1 trait • dwarfism (achondroplasia) • gigantism (acromegaly)

20. Acromegaly: André the Giant

21. Inheritance pattern of Achondroplasia Aa x aa Aa x Aa a a A a  Aa A Aa A AA Aa a a aa aa Aa aa 50% dwarf:50% normal or1:1 67% dwarf:33%normalor2:1

22. Many genes: one trait • Polygenic inheritance • additive effects of many genes • humans • skin color • height • weight • eye color • intelligence • behaviors

23. Human skin color • AaBbCc x AaBbCc • can produce a wide range of shades • most children = intermediate skin color • some can be very light & very dark

24. Johnny & Edgar Winter Albinism albinoAfricans melanin = universal brown color

25. OCA1 albino Bianca Knowlton

26. Coat color in other animals • 2 genes: E,eandB,b • color (E) or no color (e) • how dark color will be: black (B) or brown(b) eebb eeB– E–bb E–B–

27. Environment effect on genes • Phenotype is controlled by both environment & genes Coat color in arctic fox influenced by heat sensitive alleles Human skin color is influenced by both genetics & environmental conditions Color of Hydrangea flowers is influenced by soil pH

28. Genetics of sex • Women & men are very different, but just a few genes create that difference • In mammals = 2 sex chromosomes • X & Y • 2 X chromosomes = female: XX • X & Y chromosome = male: XY X X X Y

29. Sex chromosomes

30. Sex-linked traits • Sex chromosomes have other genes on them, too • especially the X chromosome • hemophilia in humans • blood doesn’t clot • Duchenne muscular dystrophy in humans • loss of muscle control • red-green color blindness • see green & red as shades of grey X X X Y

31. HH XHXH XHXh XHXh XHXh Hh XH XHY XHY XhY Xh male / sperm XH Y XHXH XHY XH XHY XH female / eggs Y Xh XhY XHXh Sex-linked traits sex-linked recessive 2 normal parents, but mother is carrier x

34. Dominant ≠ most common allele • Because an allele is dominant does not mean… • it is better, or • it is more common Polydactyly dominant allele

35. Polydactyly individuals are born with extra fingers or toes the allele for >5 fingers/toes is DOMINANT & the allele for 5 digits is recessive recessive allele far morecommon than dominant  only 1 individual out of 500 has more than 5 fingers/toes  so 499 out of 500 people are homozygous recessive (aa)

36. Hound Dog Taylor

37. Any Questions?