2. Genetics & The Work of Mendel

3. 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 –used mathematical analysis collected data & counted them –excellent example of scientific method Gregor Mendel

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

5. Mendel collected data for 7 pea traits

6. 2 nd generation 3:1 75% purple-flower peas 25% white-flower peas Looking closer at Mendel’s work Parents 100% 1 st generation (hybrids) 100% purple-flower peas X true-breeding purple-flower peas true-breeding white-flower peas self-pollinate

7. 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 purple masked white –dominant allele functional protein –affects characteristic masks other alleles –recessive allele no noticeable effect allele makes a non-functioning protein homologous chromosomes I’ll speak for both of us! allele producing functional protein mutant allele malfunctioning protein

8. 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 F1F1 P X purplewhite all purple

9. 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 x pp PpPp F1F1 P X purplewhite all purple

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

11. Any Questions??

12. 2007-2008 Beyond Mendel’s Laws of Inheritance

13. 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!

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

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

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

17. Codominance Equal dominance –human ABO blood groups –3 versions 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

18. Blood donation 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. Aa x aa Inheritance pattern of Achondroplasia aa A a Aa A a Aa x Aa Aa aa Aa 50% dwarf:50% normal or 1:1 AA aa Aa 67% dwarf:33% normal or 2:1 Aa

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. Albinism Johnny & Edgar Winter melanin = universal brown color

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

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

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 XY XX

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 XY XX

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

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

35. Hound Dog Taylor