Chapter 15 - Beyond Mendelian Genetics


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Chapter 15 - Beyond Mendelian Genetics

  1. 1. Beyond Mendel’s Laws of InheritanceAP Biology 2006-2007
  2. 2. Extending Mendelian genetics  Mendel worked with a simple system  peas are genetically simple  most traits are controlled by a single gene  each gene has only 2 alleles, 1 of which is completely dominant to the other  The relationship between genotype & phenotype is rarely that simpleAP Biology
  3. 3. Incomplete dominance  Heterozygote shows an intermediate, blended phenotype  example:  RR = red flowers RR  rr = white flowers WW  Rr = pink flowers RW  make 50% less colorAP Biology RR RW WW
  4. 4. Incomplete dominance true-breeding X true-breeding P red flowers white flowers 100% pink flowers F1 generation 100% (hybrids) It’s like self-pollinate flipping 2 pennies! 25% 50% 25% red pink white 1:2:1 F2 generationAP Biology
  5. 5. Co-dominance  2 alleles affect the phenotype equally & separately  not blended phenotype  human ABO blood groups  3 alleles  IA, IB, i  IA & IB alleles are co-dominant  glycoprotein antigens on RBC  IAIB = both antigens are produced  i allele recessive to bothAP Biology
  6. 6. Genetics of Blood typepheno- antigen antibodies donation genotype type on RBC in blood status type A antigens A IA IA or IA i on surface of RBC anti-B antibodies __ type B antigens B IB IB or IB i on surface of RBC anti-A antibodies __ both type A & type B antigens universal AB IA IB on surface no antibodies recipient of RBC no antigens universal anti-A & anti-B O ii on surface of RBC antibodies donorAP Biology
  7. 7. Pleiotropy  Most genes are pleiotropic  one gene affects more than one phenotypic character  1 gene affects more than 1 trait  dwarfism (achondroplasia)  gigantism (acromegaly)AP Biology
  8. 8. Acromegaly: André the GiantAP Biology
  9. 9. Inheritance pattern of Achondroplasia Aa x aa Aa x Aa dominant inheritance a a A a A Aa dwarf Aa dwarf A  AA lethal Aa a aa aa a Aa aa 50% dwarf:50%AP Biology normal or 1:1 67% dwarf:33% normal or 2:1
  10. 10. Epistasis  One gene completely masks another gene  coat color in mice = 2 separate genes  C,c: pigment (C) orB_C_ no pigment (c)  B,b:bbC_ more pigment (black=B) or less (brown=b)_ _cc  cc = albino, no matter B allele  9:3:3:1 becomes 9:3:4 How would you know that difference wasn’t random chance?AP Biology Chi-square test!
  11. 11. Epistasis in Labrador retrievers  2 genes: (E,e) & (B,b)  pigment (E) or no pigment (e)  pigment concentration: black (B) to brown (b) eebb eeB– E–bb E–B–AP Biology
  12. 12. Polygenic inheritance  Some phenotypes determined by additive effects of 2 or more genes on a single character  phenotypes on a continuum  human traits  skin color  height  weight  intelligence  behaviorsAP Biology
  13. 13. Johnny & Edgar Winter Skin color: Albinism  However albinism can be inherited as a single gene trait  aa = albino albino Africansmelanin = universal brown color enzyme melanintyrosine AP Biology albinism
  14. 14. OCA1 albino Bianca KnowltonAP Biology
  15. 15. 1910 | 1933 Sex linked traits  Genes are on sex chromosomes  as opposed to autosomal chromosomes  first discovered by T.H. Morgan at Columbia U.  Drosophila breeding  good genetic subject  prolific  2 week generations  4 pairs of chromosomes  XX=female, XY=maleAP Biology
  16. 16. Classes of chromosomes autosomal chromosomes sex chromosomesAP Biology
  17. 17. Discovery of sex linkage true-breeding true-breeding red-eye female X white-eye maleP Huh! Sex matters?! 100%F1 red eye offspringgeneration(hybrids) 100% 50% red-eye male red-eye female 50% white eye maleF2generationAP Biology
  18. 18. What’s up with Morgan’s flies? x x RR rr Rr Rr r r R r R Rr Rr R RR Rr Doesn’t work that way! R Rr Rr r Rr rrAP Biology 100% red eyes 3 red : 1 white
  19. 19. Genetics of Sex  In humans & other mammals, there are 2 sex chromosomes: X & Y  2 X chromosomes  develop as a female: XX  gene redundancy, like autosomal chromosomes  an X & Y chromosome X Y  develop as a male: XY  no redundancy X XX XY X XX XYAP Biology 50% female : 50% male
  20. 20. Let’s reconsider Morgan’s flies… x x X R XR X rY XR Xr XRY  Xr Y XR Y XR XR XR Xr XRY XR XR XRY BINGO! XR Xr XR Xr XRY XR Xr X rY 100% red femalesAP Biology 100% red eyes 50% red males; 50% white males
  21. 21. Genes on sex chromosomes  Y chromosome  few genes other than SRY  sex-determining region  master regulator for maleness  turns on genes for production of male hormones  many effects = pleiotropy!  X chromosome  other genes/traits beyond sex determination  mutations:  hemophiliaAP Biology  Duchenne muscular dystrophy
  22. 22. Ichthyosis, X-linked Placental steroid sulfatase deficiency Human X chromosome Kallmann syndrome Chondrodysplasia punctata, X-linked recessive Hypophosphatemia  Sex-linked Aicardi syndrome Duchenne muscular dystrophy Hypomagnesemia, X-linked Becker muscular dystrophy Ocular albinism Retinoschisis Chronic granulomatous disease Retinitis pigmentosa-3 Adrenal hypoplasia  usually Norrie disease Retinitis pigmentosa-2 Glycerol kinase deficiency Ornithine transcarbamylase deficiency means Incontinentia pigmenti Wiskott-Aldrich syndrome “X-linked” Menkes syndrome Androgen insensitivity Sideroblastic anemia Charcot-Marie-Tooth neuropathy  more than Aarskog-Scott syndrome Choroideremia PGK deficiency hemolytic anemia Cleft palate, X-linked Spastic paraplegia, X-linked, Anhidrotic ectodermal dysplasia 60 diseases Agammaglobulinemia uncomplicated Deafness with stapes fixation PRPS-related gout Kennedy disease traced to Pelizaeus-Merzbacher disease Alport syndrome Lowe syndrome Fabry disease Lesch-Nyhan syndrome genes on X Immunodeficiency, X-linked, HPRT-related gout Hunter syndrome with hyper IgM Hemophilia B chromosome Lymphoproliferative syndrome Hemophilia A G6PD deficiency: favism Drug-sensitive anemia Albinism-deafness syndrome Chronic hemolytic anemia Manic-depressive illness, X-linked Fragile-X syndrome Colorblindness, (several forms) Dyskeratosis congenita TKCR syndrome Adrenoleukodystrophy Adrenomyeloneuropathy Emery-Dreifuss muscular dystrophyAP Biology Diabetes insipidus, renal Myotubular myopathy, X-linked
  23. 23. AP Biology
  24. 24. sex-linked recessive Hemophilia XHhh x XHY HX HH XH male / sperm X H Xh XH Y Xh female / eggs XH XH X H XH Y XH XH Y Xh XH Xh XhY YAP Biology carrier disease
  25. 25. X-inactivation  Female mammals inherit 2 X chromosomes  one X becomes inactivated during embryonic development  condenses into compact object = Barr body  which X becomes Barr body is random  patchwork trait = “mosaic” patches of black XH  XH Xhtricolor cats Xhcan only be AP Biologyfemale patches of orange
  26. 26. Male pattern baldness  Sex influenced trait  autosomal trait influenced by sex hormones  age effect as well = onset after 30 years old  dominant in males & recessive in females  B_ = bald in males; bb = bald in femalesAP Biology
  27. 27. Environmental effects  Phenotype is controlled by both environment & genes Human skin color is influenced by both genetics & environmental conditions Coat color in arctic fox influenced by heat sensitive allelesColor of Hydrangea flowers AP Biologyis influenced by soil pH
  28. 28. Any Questions?AP Biology 2006-2007