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Transcript
AP Biology 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 Beyond Mendel Mendel’s s Laws of Inheritance The relationship between genotype & phenotype is rarely that simple AP Biology 2006-2007 Incomplete dominance Heterozygote shows an intermediate, blended phenotype example: RR = red flowers →RR rr = white flowers →WW Rr = pink flowers →RW AP Biology Incomplete dominance P X true-breeding red flowers true-breeding white flowers 100% pink flowers F1 100% generation (hybrids) make 50% less color self-pollinate 25% red 50% pink 25% white It’s like flipping 2 pennies! 1:2:1 F2 AP Biology RR RW WW generation AP Biology 1 AP Biology Co-dominance 2 alleles affect the phenotype equally & separately not blended phenotype human ABO blood groups 3 alleles IA, IB, phenogenotype type antigen on RBC antibodies in blood donation status IA IA or IA i type A antigens on surface of RBC anti-B antibodies __ IB IB or IB i type B antigens on surface of RBC anti-A antibodies __ AB IA IB both type A & type B antigens on surface of RBC no antibodies universal recipient O ii no antigens on surface of RBC anti-A & anti-B antibodies universal donor A B i IA & IB alleles are co-dominant glycoprotein antigens on RBC IAIB = both antigens are produced i allele recessive to both AP Biology AP Biology Pleiotropy Most genes are pleiotropic Genetics of Blood type Acromegaly: André the Giant one gene affects more than one phenotypic character 1 gene affects more than 1 trait dwarfism d fi (achondroplasia) ( h d l i ) gigantism (acromegaly) AP Biology AP Biology 2 AP Biology Inheritance pattern of Achondroplasia Aa Aa x aa x Aa Epistasis One gene completely masks another gene coat color in mice = 2 separate genes dominant inheritance A a a a Aa Aa dwarf dwarf aa aa 50% dwarf:50% AP Biology A a AA Aa Aa aa 67% dwarf:33% normal or 2:1 Epistasis in Labrador retrievers 2 genes: (E,e) & (B,b) B_C_ B,b: more pigment (black=B) or less (brown=b) bbC_ _ _cc lethal a normal or 1:1 A C,c: pigment (C) or no pigment (c) pigment (E) or no pigment (e) pigment concentration: black (B) to brown (b) cc = albino, no matter B allele 9:3:3:1 becomes 9:3:4 AP Biology How would you know that difference wasn’t random chance? Chi-square test! 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 eebb eeB– E–bb intelligence E–B– behaviors AP Biology AP Biology 3 AP Biology Skin color: Albinism Johnny & Edgar Winter OCA1 albino Bianca Knowlton However albinism can be inherited as a single gene trait aa = albino albino Africans melanin = universal brown color enzyme tyrosine AP Biology melanin AP Biology albinism Sex linked traits 1910 | 1933 Classes of chromosomes Genes are on sex chromosomes as opposed to autosomal chromosomes first discovered by T.H. Morgan at Columbia U. Drosophila breeding autosomal good genetic ge et c subject prolific 2 week generations 4 pairs of chromosomes XX=female, XY=male chromosomes sex chromosomes AP Biology AP Biology 4 AP Biology Discovery of sex linkage true-breeding red-eye female P X What’s up with Morgan’s flies? true-breeding white-eye male RR Huh! Sex matters?! 100% red eye offspring F1 r generation (hybrids) R 100% red-eye female F2 x 50% red-eye male 50% white eye male R Genetics of Sex Rr R Rr r RR Rr Rr Rr rr r 3 red : 1 white Let’s reconsider Morgan’s flies… XRXR 2 X chromosomes develop as a female: XX gene redundancy redundancy, like autosomal chromosomes an X & Y chromosome X Y XR develop as a male: XY X X XX XX XY x x sex chromosomes: X & Y 50% female : 50% male R 100% red eyes In humans & other mammals, there are 2 AP Biology r Rr AP Biology no redundancy Rr Doesn’t work that way! AP Biology rr Rr generation x XR XY AP Biology XrY Xr Y XRXr XRY XRXr XRY 100% red eyes XR BINGO! Xr XRXr XRY XR Y XRXR XRY XRXr XrY 100% red females 50% red males; 50% white males 5 AP Biology Genes on sex chromosomes Y chromosome Human X chromosome Sex-linked Duchenne muscular dystrophy Becker muscular dystrophy few genes other than SRY sex-determining region master regulator for maleness turns t on genes for f production d ti off male l hormones h many effects = pleiotropy! X chromosome AP Biology usually means “X-linked” more than th 60 diseases traced to genes on X chromosome other genes/traits beyond sex determination Chronic granulomatous disease Retinitis pigmentosa-3 Norrie disease Retinitis pigmentosa-2 Adrenal hypoplasia Glycerol kinase deficiency Ornithine transcarbamylase deficiency Androgen insensitivity Sideroblastic anemia Aarskog-Scott syndrome PGK deficiency hemolytic anemia Anhidrotic ectodermal dysplasia Agammaglobulinemia Kennedy disease Pelizaeus-Merzbacher disease Alport syndrome Fabry disease Immunodeficiency, X-linked, with hyper IgM Lymphoproliferative syndrome Fragile-X syndrome AP Biology Hypophosphatemia Aicardi syndrome Hypomagnesemia, X-linked Ocular albinism Retinoschisis Incontinentia pigmenti Wiskott-Aldrich syndrome Menkes syndrome Albinism-deafness syndrome mutations: hemophilia Duchenne muscular dystrophy Ichthyosis, X-linked Placental steroid sulfatase deficiency Kallmann syndrome Chondrodysplasia punctata, X-linked recessive Charcot-Marie-Tooth neuropathy Choroideremia Cleft palate, X-linked Spastic paraplegia, X-linked, uncomplicated Deafness with stapes fixation PRPS-related gout Lowe syndrome Lesch-Nyhan syndrome HPRT-related gout Hunter syndrome Hemophilia B Hemophilia A G6PD deficiency: favism Drug-sensitive anemia Chronic hemolytic anemia Manic-depressive illness, X-linked Colorblindness, (several forms) Dyskeratosis congenita TKCR syndrome Adrenoleukodystrophy Adrenomyeloneuropathy Emery-Dreifuss muscular dystrophy Diabetes insipidus, renal Myotubular myopathy, X-linked 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) Devotion to sports (BUD-E) Addiction to death & destruction movies (SAW-2) note: t nott li linked k d to t ability bilit gene Air guitar (RIF) Scratching (ITCH-E) Spitting (P2E) Inability to express affection over phone (ME-2) AP Biology linked Selective hearing loss (HUH) Total lack of recall for dates (OOPS) AP Biology 6 AP Biology sex-linked recessive Hemophilia HXh x X HY HH XHh XH male / sperm XH X-inactivation Female mammals inherit 2 X chromosomes XHXh Y Xh one X becomes inactivated during embryonic development condenses into compact object = Barr body which X becomes Barr body y is random patchwork trait = “mosaic” female / eggs patches of black XH XHXH XHY XH XH Xh AP Biology XHXh carrier XhY XHY XHXh Y disease 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 Xh tricolor cats can only be AP Biology female patches of orange 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 alleles AP Biology Color of Hydrangea flowers APinfluenced Biology is by soil pH 7 AP Biology Any Questions? AP Biology 2006-2007 8
