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Genetics and Mendel Chapters 11 and 12 AP Biology 2006-2007 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 AP Biology Gregor Johann Mendel Austrian Monk, born in what is now Czech Republic in 1822 Son of peasant farmer, studied Theology and was ordained priest Order St. Augustine. Went to the university of Vienna, where he studied botany and learned the Scientific Method Worked with pure lines of peas for eight years Prior to Mendel, heredity was regarded as a "blending” process and the offspring were essentially a "dilution"of the different parental APcharacteristics. Biology Genetics terms you need to know: Gene – a unit of heredity; a section of DNA sequence encoding a single protein Genome – the entire set of genes in an organism Alleles – two genes that occupy the same position on homologous chromosomes and that cover the same trait (like ‘flavors’ of a trait). Locus – a fixed location on a strand of DNA where a gene or one of its alleles is located. AP Biology Homozygous – having identical genes (one from each parent) for a particular characteristic. Heterozygous – having two different genes for a particular characteristic. Dominant – the allele of a gene that masks or suppresses the expression of an alternate allele; the trait appears in the heterozygous condition. Recessive – an allele that is masked by a dominant allele; does not appear in the heterozygous condition, only in homozygous. AP Biology Genotype – the genetic makeup of an organism Phenotype – the physical appearance of an organism (Genotype + environment) Monohybrid cross: a genetic cross involving a single pair of genes (one trait); parents differ by a single trait. P = Parental generation F1 = First filial generation; offspring from a genetic cross. F2 = Second filial generation of a genetic cross AP Biology Another example: Flower color For example, flower color: P = purple (dominant) p = white (recessive) If you cross a homozygous Purple (PP) with a homozygous white (pp): PP Pp AP Biology pp ALL PURPLE (Pp) Cross the F1 generation: Pp P p AP Biology Pp P p PP Pp Pp pp Genotypes: 1 PP 2 Pp 1 pp Phenotypes: 3 Purple 1 White Incomplete dominance Heterozygote shows an intermediate, blended phenotype example: RR = red flowers rr = white flowers Rr = pink flowers make 50% less color AP Biology RR Rr rr Incomplete dominance P X true-breeding red flowers true-breeding white flowers 100% pink flowers F1 100% generation (hybrids) self-pollinate 25% red F2 generation AP Biology 50% pink 25% white 1:2:1 Incomplete dominance CRCW x C RCW % genotype female / eggs male / sperm CR CW CR CW _____ _____ CRCR CRCW ____ ____ ____ ____ CRCW _____ _____ C WC W ____ ____ 1:2:1 AP Biology % phenotype 1:2:1 Co-dominance 2 alleles affect the phenotype equally & separately not blended phenotype example: ABO blood groups 3 alleles IA, IB, i IA & IB alleles are co-dominant to each other both antigens are produced both IA & IB are dominant to i allele AP Biology produces glycoprotein antigen markers on the surface of red blood cells Genetics of Blood type phenogenotype type A B AB O AP Biology 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 __ IA IB both type A & type B antigens on surface of RBC no antibodies universal recipient ii no antigens on surface of RBC anti-A & anti-B antibodies universal donor Blood compatibility 1901 | 1930 Matching compatible blood groups critical for blood transfusions A person produces antibodies against antigens in foreign blood wrong blood type donor’s blood has A or B antigen that is foreign to recipient antibodies in recipient’s blood bind to foreign molecules cause donated blood cells to clump together can kill the recipient AP Biology Karl Landsteiner (1868-1943) Blood donation clotting clotting clotting clotting AP Biology clotting clotting clotting Pleiotropy Most genes are pleiotropic one gene affects more than one phenotypic character wide-ranging effects due to a single gene dwarfism (achondroplasia) gigantism (acromegaly) AP Biology Acromegaly: André the Giant AP Biology Inheritance pattern of Achondroplasia Aa x aa a a A ____ ____ a ____ 50% dwarf:50% AP Biology Aa x Aa A a A ____ ____ ____ a ____ ____ normal or 1:1 67% dwarf:33% normal or 2:1 Epistasis One gene completely another gene coat color in mice = 2 separate genes C,c: pigment (C) or no pigment (c) B,b: more pigment (black=B) or less (brown=b) cc = albino, no matter B allele 9:3:3:1 becomes 9:3:4 AP Biology Epistasis in Labrador retrievers 2 genes: (E,e) & (B,b) pigment (E) or no pigment (e) pigment concentration: black (B) to brown (b) eebb AP Biology eeB– E–bb E–B– 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 eye color intelligence behaviors AP Biology Skin color: Albinism Johnny & Edgar Winter However albinism can be inherited as a single gene trait albino Africans melanin = universal brown color enzyme tyrosine AP Biology melanin albinism OCA1 albino AP Biology Bianca Knowlton Sex linked traits 1910 | 1933 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 AP Biology Classes of chromosomes autosomal chromosomes sex chromosomes AP Biology Discovery of sex linkage P F1 true-breeding red-eye female X true-breeding white-eye male 100% red eye offspring generation (hybrids) F2 generation AP Biology 100% red-eye female 50% red-eye male 50% white eye male 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 develop as a male: XY no redundancy AP Biology 50% female : 50% male What’s up with Morgan’s flies? x _____ ____ ____ ____ x _____ ____ _____ _____ _____ _____ AP Biology _____ 100% red eyes ____ ____ ____ _____ ____ _____ _____ _____ _____ 100% red females 50% red males; 50% white males 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 AP Biology other traits beyond sex determination mutations: hemophilia Duchenne muscular dystrophy color-blindness Human X chromosome Sex-linked Duchenne muscular dystrophy Becker muscular dystrophy usually means “X-linked” more than 60 diseases traced to genes on X chromosome Chronic granulomatous disease Retinitis pigmentosa-3 Norrie disease Retinitis pigmentosa-2 Hypophosphatemia Aicardi syndrome Hypomagnesemia, X-linked Ocular albinism Retinoschisis Adrenal hypoplasia Glycerol kinase deficiency Ornithine transcarbamylase deficiency Incontinentia pigmenti Wiskott-Aldrich syndrome Menkes syndrome 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 Albinism-deafness syndrome Fragile-X syndrome AP Biology 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 AP Biology Sex-determining Region Y (SRY) Sex-linked traits summary X-linked follow the X chromosomes males get their X from their mother trait is never passed from father to son Y-linked very few genes / traits trait is only passed from father to son females cannot inherit trait AP Biology AP Biology AP Biology sex-linked recessive Hemophilia Hh x HH female / eggs male / sperm ___ ___ carrier disease ___ ___ AP Biology 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” XH XH X h Xh AP Biology X-inactivation & tortoise shell cat 2 different cell lines in cat AP Biology 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 AP Biology Nature vs. nurture 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 Color of Hydrangea flowers APinfluenced Biology is by soil pH Any Questions? AP Biology