Chapter 13 (part 2) - Beyond Mendel
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Chapter 13 (part 2) - Beyond Mendel






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Chapter 13 (part 2) - Beyond Mendel Presentation Transcript

  • 1. Beyond Mendel’s Laws of Inheritance 2006-2007
  • 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 simple
  • 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 color RR RW WW
  • 4. Incomplete dominance true-breeding X true-breedingP red flowers white flowers 100% pink flowersF1generation 100%(hybrids) It’s like self-pollinate flipping 2 pennies! 25% 50% 25% red pink white 1:2:1F2generation
  • 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 both
  • 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 donor
  • 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)
  • 8. Acromegaly: André the Giant
  • 9. Inheritance pattern of Achondroplasia Aa x aa Aa x Aa dominant inheritance a a A aA Aa dwarf Aa dwarf A  AA lethal Aaa aa aa a Aa aa50% dwarf:50% normal or 1:1 67% dwarf:33% normal or 2:1
  • 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? Chi-square test!
  • 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–
  • 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  behaviors
  • 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 albinism
  • 14. OCA1 albino Bianca Knowlton
  • 15. 1910 | 1933Sex 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=male
  • 16. Classes of chromosomes autosomal chromosomes sex chromosomes
  • 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 maleF2generation
  • 18. What’s up with Morgan’s flies? x x RR rr Rr Rr r r R rR Rr Rr R RR Rr Doesn’t work that way!R Rr Rr r Rr rr 100% red eyes 3 red : 1 white
  • 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 XY 50% female : 50% male
  • 20. Let’s reconsider Morgan’s flies… x x X R XR X rY XR Xr XRY Xr Y XR YXR XR XR Xr XRY XR XR XRY BINGO!XR Xr XR Xr XRY XR Xr X rY 100% red females 100% red eyes 50% red males; 50% white males
  • 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:  hemophilia  Duchenne muscular dystrophy  color-blindness
  • 22. Ichthyosis, X-linked Placental steroid sulfatase deficiencyHuman 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 dystrophy Diabetes insipidus, renal Myotubular myopathy, X-linked
  • 23. Map of Human Y chromosome?< 30 genes onY chromosome Sex-determining Region Y (SRY) Channel Flipping (FLP) Catching & Throwing (BLZ-1) Self confidence (BLZ-2) note: not linked to ability geneDevotion to sports (BUD-E) Addiction to death &destruction movies (SAW-2) Air guitar (RIF) Scratching (ITCH-E) Spitting (P2E) linked Inability to expressaffection over phone (ME-2) Selective hearing loss (HUH) Total lack of recall for dates (OOPS)
  • 24. sex-linked recessiveHemophilia XHhh x XHY HX HH XH male / sperm X H Xh XH Y Xhfemale / eggs XH XH X H XH Y XH XH Y Xh XH Xh XhY Y carrier disease
  • 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 befemale patches of orange
  • 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 females
  • 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 flowersis influenced by soil pH
  • 28. Any Questions? 2006-2007