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58 ch13beyondmendel2008


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  • The genes that we have covered so far affect only one phenotypic character, but most genes are pleiotropic
  • Duchenne muscular dystrophy affects one in 3,500 males born in the United States. Affected individuals rarely live past their early 20s. This disorder is due to the absence of an X-linked gene for a key muscle protein, called dystrophin. The disease is characterized by a progressive weakening of the muscles and loss of coordination.
  • Hemophilia is a sex-linked recessive trait defined by the absence of one or more clotting factors. These proteins normally slow and then stop bleeding. Individuals with hemophilia have prolonged bleeding because a firm clot forms slowly. Bleeding in muscles and joints can be painful and lead to serious damage. Individuals can be treated with intravenous injections of the missing protein.
  • The relative importance of genes & the environment in influencing human characteristics is a very old & hotly contested debate a single tree has leaves that vary in size, shape & color, depending on exposure to wind & sun for humans, nutrition influences height, exercise alters build, sun-tanning darkens the skin, and experience improves performance on intelligence tests even identical twins — genetic equals — accumulate phenotypic differences as a result of their unique experiences
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    • 1. Beyond Mendel’s Laws of InheritanceAP Biology 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 simpleAP Biology
    • 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. 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. 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. Genetics of Blood typepheno- antigen antibodies donation genotype type on RBC in blood status type A antigens A I I A A or A I 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. 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. Acromegaly: André the GiantAP Biology
    • 9. Inheritance pattern of Achondroplasia Aa x aa Aa x Aa dominant inheritance a a A a A Aa Aa A AA Aa dwarf dwarf lethal a aa aa a Aa aa 50% dwarf:50%AP Biology 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?AP Biology 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–AP Biology
    • 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. Johnny & Edgar Winter Skin color: Albinism  However albinism can be inherited as a single gene trait  aa = albino albino Africansmelanin = universal brown color enzymetyrosine AP Biology melanin albinism
    • 14. OCA1 albino Bianca KnowltonAP Biology
    • 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. Classes of chromosomes autosomal chromosomes sex chromosomesAP Biology
    • 17. Discovery of sex linkage true-breeding true-breeding XP red-eye female white-eye male Huh! Sex matters?! 100%F1 red eye offspringgeneration(hybrids) 100% 50% red-eye male red-eye female 50% white eye maleF2generationAP Biology
    • 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. 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. Let’s reconsider Morgan’s flies… x x XR X R XrY X R Xr XR Y Xr Y XR Y XR XR XR Xr XR Y XR X R XR Y BINGO! XR Xr XR Xr XR Y XR Xr XrY 100% red femalesAP Biology 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 dystrophyAP Biology  color-blindness
    • 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 usually Retinitis pigmentosa-3 Adrenal hypoplasia  Glycerol kinase deficiency Norrie disease Retinitis pigmentosa-2 Ornithine transcarbamylase means deficiency Incontinentia pigmenti Wiskott-Aldrich syndrome “X-linked” Menkes syndrome Androgen insensitivity Sideroblastic anemia Charcot-Marie-Tooth neuropathy  more than Aarskog-Scott syndrome PGK deficiency hemolytic anemia Choroideremia Cleft palate, X-linked Spastic paraplegia, X-linked, 60 diseases Anhidrotic ectodermal dysplasia uncomplicated Deafness with stapes fixation Agammaglobulinemia Kennedy disease PRPS-related gout traced to Pelizaeus-Merzbacher disease Alport syndrome Lowe syndrome Lesch-Nyhan syndrome genes on X Fabry disease HPRT-related gout Immunodeficiency, X-linked, 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. Map of Human Y chromosome? < 30 genes on Y chromosome Sex-determining Region Y (SRY) Channel Flipping (FLP) Catching & Throwing (BLZ-1) Self confidence (BLZ-2) note: not linked to ability gene Devotion to sports (BUD-E) Addiction to death & destruction movies (SAW-2) Air guitar (RIF) Scratching (ITCH-E) Spitting (P2E) linked Inability to express affection over phone (ME-2) Selective hearing loss (HUH) Total lack of recall for dates (OOPS)AP Biology
    • 24. AP Biology
    • 25. sex-linked recessive Hemophilia XHhh x XHY H X HH XH male / sperm XH X h XH Y Xh X HY female / eggs X H XH X H XH X HY Xh X H Xh Xh Y YAP Biology carrier disease
    • 26. 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 X htricolor cats Xhcan only befemale AP Biology patches of orange
    • 27. 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
    • 28. 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
    • 29. Any Questions?AP Biology 2006-2007