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Extending Mendelian genetics
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Extending Mendelian genetics


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  • 1. 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 Non-Mendelian Inheritance is completely dominant to the other • The relationship between genotype & phenotype is _______ that simple Incomplete dominance Incomplete dominance • Both alleles of a trait are __________ P true-breeding X true-breeding expressed; a blend or mixture of alleles red flowers white flowers – example: • RR = red flowers →RR 100% pink flowers • rr = white flowers →WW F1 • Rr = pink flowers →RW generation 4:0 – make 50% less color (hybrids) self-pollinate 25% 50% 25% red pink white 1:2:1 F2 generation RR RW WW Genetics of Blood type Co-dominance • Both alleles for a trait are both _______ pheno- antigen antibodies donation genotype expressed; no blend/mix type on RBC in blood status ______ antigens – human ABO blood groups A on surface anti-B antibodies of RBC – 3 alleles ______ antigens • IA, IB, i B on surface anti-A antibodies • IA & IB alleles are co-dominant of RBC – glycoprotein antigens on RBC ______________ ______ antigens – IAIB = both antigens are produced AB on surface no antibodies _______ • i allele recessive to both of RBC ______________ anti-A & anti-B O on surface of RBC antibodies _______ 1
  • 2. Pleiotropy Inheritance pattern of • Most genes are pleiotropic Achondroplasia – __________________________________ Aa x aa Aa x Aa • dwarfism (achondroplasia) dominant inheritance • gigantism (acromegaly) a a A a A Aa dwarf Aa dwarf A ✗ AA lethal Aa a aa aa a Aa aa 50% dwarf:50% normal or 2:2 67% dwarf:33% normal or 2:1:1 Epistasis • __________________________________ Polygenic inheritance __________________________________ • Some phenotypes determined by _____ – coat color in mice = 2 separate genes ________________________________ • C,c: – human traits pigment (C) or B_C_ • skin color no pigment (c) • height bbC_ • B,b: black=B • weight brown=b • intelligence _ _cc • cc = albino, • behaviors no matter B allele • 9:3:3:1 becomes 9:3:4 Skin color: Albinism Sex linked traits • Some genes are on sex chromosomes • However albinism can be – as opposed to autosomal chromosomes inherited as a single gene trait – first discovered by T.H. Morgan at Columbia U. – ___ = albino – Drosophila breeding • good genetic subject – ___________________ – ___________________ melanin = universal brown color enzyme tyrosine melanin albinism 2
  • 3. Classes of chromosomes Discovery of sex linkage true-breeding true-breeding X P red-eye female white-eye male 100% red eye offspring F1 generation 100% 50% red-eye male red-eye female 50% white eye male F2 generation If autosomal, how can this be? Sex Linked Traits x x • In humans & other mammals, there are 2 sex chromosomes: X & Y RR rr Rr Rr – 2 X chromosomes • develop as a female: XX r r R r • _____________________, like autosomal chromosomes R Rr Rr R RR Rr – an X & Y chromosome X Y • develop as a male: XY • _____________ X XX XY R Rr Rr r Rr rr X XX XY 100% red eyes 3 red : 1 white 50% female : 50% male Another look at fly’s eye color Genes on sex chromosomes • Y chromosome – few genes other than _______________ x x • Expresses the production of ____________ XRXR XrY XRXr XRY – many effects = pleiotropy! – Express male ___________________________ Xr Y XR Y – Express male secondary sexual characteristics • X chromosome XR XR – other genes/traits beyond sex determination XRXr XRY XRXR XRY • mutations: – hemophilia XR Xr – Duchenne muscular dystrophy XRXr XRY XRXr XrY – color-blindness 100% red females 100% red eyes 50% red males; 50% white males 3
  • 4. Human X chromosome Ichthyosis, X-linked Map of Human Y chromosome? Placental steroid sulfatase deficiency Kallmann syndrome Chondrodysplasia punctata, X-linked recessive Hypophosphatemia Aicardi syndrome • Sex-linked Duchenne muscular dystrophy Becker muscular dystrophy Hypomagnesemia, X-linked Ocular albinism Retinoschisis ____ genes on Chronic granulomatous disease – usually means Y chromosome Sex-determining Region Y (SRY) Retinitis pigmentosa-3 Adrenal hypoplasia Glycerol kinase deficiency Norrie disease Retinitis pigmentosa-2 Ornithine transcarbamylase “X-linked” deficiency Channel Flipping (FLP) Incontinentia pigmenti Wiskott-Aldrich syndrome Menkes syndrome Catching & Throwing (BLZ-1) – more than Sideroblastic anemia Androgen insensitivity Self confidence (BLZ-2) Charcot-Marie-Tooth neuropathy note: not linked to ability gene 60 diseases Aarskog-Scott syndrome PGK deficiency hemolytic anemia Choroideremia Cleft palate, X-linked Spastic paraplegia, X-linked, Devotion to sports (BUD-E) traced to Anhidrotic ectodermal dysplasia uncomplicated Deafness with stapes fixation Addiction to death & Agammaglobulinemia Kennedy disease PRPS-related gout destruction movies (SAW-2) Air guitar (RIF) genes on X Pelizaeus-Merzbacher disease Alport syndrome Lowe syndrome Lesch-Nyhan syndrome Fabry disease chromosome Immunodeficiency, X-linked, with hyper IgM HPRT-related gout Hunter syndrome Hemophilia B Scratching (ITCH-E) Lymphoproliferative syndrome Hemophilia A Spitting (P2E) linked 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 Inability to express TKCR syndrome Adrenoleukodystrophy affection over phone (ME-2) Selective hearing loss (HUH) Adrenomyeloneuropathy Emery-Dreifuss muscular dystrophy Total lack of recall for dates (OOPS) Diabetes insipidus, renal Myotubular myopathy, X-linked Hemophilia sex-linked recessive XHXh x XHY Hh HH XH male / sperm XHXh XH Y Xh XHY female / eggs XH XHXH XH XHY Xh XHXh XhY Y carrier disease Red-Green Colorblindness Environmental effects • X sex-linked trait – Recessive • Phenotype is controlled by – More prevalent in males than females both ___________________ • Why? Human skin color is influenced by both genetics & environmental conditions Coat color in arctic fox influenced by heat sensitive alleles Color of Hydrangea flowers is influenced by soil pH 4