2. Regents Biology 2007-2008 Genetics & The Work of Mendel

3. Regents Biology  Modern genetics began in the mid- 1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in peas  Contributed to research in heredity: transmission of characteristics from parents to offspring  used good experimental design  used mathematical analysis  collected data & counted them  excellent example of scientific method Gregor Mendel

4. Regents Biology Section 1 Mendel’s Legacy Chapter 9 Gregor Mendel, continued  Mendel’s Garden Peas  Mendel observed characteristics of pea plants.  Traits are genetically determined variants of a characteristic.  Example:  Characteristic = eye color, trait = blue eyes  Each characteristic in the peas occurred in two contrasting traits.  Example, yellow or green peas, wrinkled or smooth peas…

5. Regents Biology Mendel collected data for 7 pea traits

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

7. Regents Biology 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

8. Regents Biology Section 1 Mendel’s Legacy Chapter 9 Support for Mendel’s Conclusions  We now know that the factors that Mendel studied are alleles, or alternative forms of a gene.  One allele for each trait is passed from each parent to the offspring.

9. Regents Biology 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 on organisms appearance when paired with dominant allele homologous chromosomes I’ll speak for both of us! allele producing observable characteristic allele with masked characteristic

10. Regents Biology Genotype vs. phenotype  Difference between how an organism “looks” & its genetics  phenotype  description of an organism’s appearance in terms of traits  genotype  description of an organism’s genetic makeup (genes) Explain Mendel’s results using …dominant & recessive …phenotype & genotype F1F1 P X purplewhite all purple

11. Regents Biology Making crosses  You 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

12. Regents Biology Section 1 Mendel’s Legacy Chapter 9 Mendel’s Results and Conclusions, continued  The Law of Segregation  The law of segregation states that allele pairs are segregated, or separated, during the formation of gametes. C:\Projects\Holt-Rinehart- Winston\HRWScience\HRWSci ence\Modern_Biology\Ch09\611 22.html

13. Regents Biology Section 1 Mendel’s Legacy Chapter 9 Mendel’s Results and Conclusions, continued  The Law of Independent Assortment  The law of independent assortment states that factors for individual characteristics are distributed to gametes independent of one another.  The law of independent assortment is observed only for genes that are located on separate chromosomes or are far apart on the same chromosome.

14. Regents Biology 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 PPPpPp PpPppp PpPp PpPp 1 st generation (hybrids) Aaaaah, phenotype & genotype can have different ratios

15. Regents Biology  Let’s work some sample problems of Punnett Squares!

16. Regents Biology 2007-2008 Beyond Mendel’s Laws of Inheritance (Non-Mendelian Genetics)

17. Regents Biology 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!

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

19. Regents Biology 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

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

21. Regents Biology Codominance  Equal dominance  human ABO blood 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

22. Regents Biology Genetics of Blood type pheno- type genotype antigen on RBC antibodies in blood donation status AA A or A i type A antigens on surface of RBC anti-B antibodies __ BBB or B i type B antigens on surface of RBC anti-A antibodies __ AB both type A & type B antigens on surface of RBC no antibodies universal recipient Oi ii i no antigens on surface of RBC anti-A & anti-B antibodies universal donor

23. Regents Biology Blood donation clotting

24. Regents Biology 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)

25. Regents Biology Acromegaly: André the Giant

26. Regents Biology 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

27. Regents Biology Many genes: one trait  Polygenic inheritance  additive effects of many genes  humans  skin color  height  weight  eye color  intelligence  behaviors

28. Regents Biology 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

29. Regents Biology Albinism Johnny & Edgar Winter albino Africans melanin = universal brown color

30. Regents Biology OCA1 albinoBianca Knowlton

31. Regents Biology 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

32. Regents Biology  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

33. Regents Biology 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

34. Regents Biology Sex chromosomes

35. Regents Biology 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

36. Regents Biology Sex-linked traits XHXH Y male / sperm XHXH XhXh female / eggs XHXHXHXH XHXhXHXh XHYXHYXhYXhY XHXhXHXh XHXH XhXh XHYXHY Y XHXH XHXHXHXH XHYXHY XHXhXHXh XhYXhY sex-linked recessive 2 normal parents, but mother is carrier HH Hh x XHYXHY XHXhXHXh

37. Regents Biology

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

40. Regents Biology 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

41. Regents Biology Hound Dog Taylor