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Transcript
Colonie High AP Biology DeMarco/Goldberg Chapter 12.2 – 12.3 Extending Mendelian Genetics Mendel worked with a simple system Beyond Mendel’s Laws of Inheritance 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 Incomplete Dominance when one allele is partially dominant 4 O’clock flowers Incomplete Dominance over the other hybrids have “in between” appearance RR = red flowers RR R = red rr = white flowers R′R′ R′ = white Rr = pink flowers RR′ Parent generation (P) RR X true-breeding red flowers R′R′ true-breeding white flowers 100% pink flowers 1st generation RR′ RR′ RR′ RR′ 100% (F1 hybrids) make 50% less color self-pollinate 2nd RR Rr Incomplete Dominance (alt) C RC W x C RC W % genotype female / eggs male / sperm CR CW CR CW C RC R C RC W C RC W % phenotype 25% 25% 50% 50% C RC W CRCW CWCW CWCW 50% pink 25% white 1:2:1 generation (F2) rr C RC R 25% red 25% 25% 1:2:1 1:2:1 Co-dominance this time, both alleles are expressed, but they are NOT blended together RR = red coat color RR R = red rr = white coat color WW W = white Rr = pink roan coat coat color? color RW Colonie High AP Biology DeMarco/Goldberg 1901 | 1930 Co-dominance 2 alleles affect the phenotype in Blood Type Compatibility Matching compatible blood groups separate, distinguishable ways ABO blood groups 3 alleles IA, IB, against oligosaccharides in foreign blood i both IA & IB are dominant to i allele I A & IB alleles are co-dominant to each other determines presences of oligosaccharides/antigens on the surface of red blood cells Blood Types genotype phenotype phenotype type B type B oligosaccharides on surface of RBC __ IA IB type AB both type A & type B oligosaccharides on surface of RBC universal recipient ii type O no oligosaccharides on surface of RBC universal donor IB IB IB i oligosaccharide that is foreign to recipient Karl Landsteiner antibodies in recipient’s blood bind to (1868-1943) foreign molecules cause donated blood cells to clump together can kill the recipient __ Pleiotropy Most genes are pleiotropic donor’s blood has A or B status type A IA i wrong blood type Blood Type Compatibility type A oligosaccharides on surface of RBC IA IA critical for blood transfusions A person produces antibodies one gene affects more than one phenotypic character wide-ranging effects due to a single gene: dwarfism (achondroplasia) gigantism vs. acromegaly Acromegaly: André the Giant Colonie High AP Biology Pleiotropy It is not surprising that a gene can affect a number of organism’s characteristics consider the intricate molecular & cellular interactions responsible for an organism’s development Epistasis One gene masks another coat color in mice = 2 genes pigment (C) or no pigment (c) more pigment (black=B) or less (brown=b) cystic fibrosis mucus build up in many organs cc = albino, sickle cell anemia sickling of blood cells 9:3:3:1 becomes 9:3:4 Epistasis in Labs 2 genes: E & B DeMarco/Goldberg no matter B allele Epistasis in People Johnny & Edgar Winter pigment (E) or no pigment (e) how dark pigment will be: black (B) to brown (b) albino Africans Polygenic Inheritance Some phenotypes determined by additive effects of 2 or more genes on a single character Nature vs. Nurture Phenotype is controlled by both environment & genes phenotypes on a continuum human traits skin color Coat color in arctic fox influenced by heat sensitive alleles height weight eye color Color of Hydrangea flowers is influenced by soil pH intelligence behaviors Human skin color is influenced by both genetics & environmental conditions Colonie High AP Biology It all started with a fly… Chromosome theory of inheritance experimental evidence from improved microscopy & animal breeding led us to a better understanding of chromosomes & genes beyond Mendel Drosophila studies DeMarco/Goldberg 1910 | 1933 Thomas Hunt Morgan embryologist at Columbia University 1st to associate a specific gene with a specific chromosome Drosophila breeding prolific 2 week generations 4 pairs of chromosomes A. H. Sturtevant in the Drosophila stockroom at Columbia University Morgan’s First Mutant… Wild type fly = red eyes Morgan found a mutant white-eyed male XX=female, XY=male Explanation of Sex Linkage red eye female traced the gene for eye color to a specific chromosome x white eye male all red eye offspring 100% of females have red eyes x 50% of males have white eyes How is this possible? Sex-linked trait! Sex-linked Traits Although differences between women & men are many, the chromosomal basis of sex is rather simple In humans & other mammals, there are 2 sex chromosomes: X & Y 2 X chromosomes develops as a female: XX an X & Y chromosome develops as a male: XY Sex Linked Traits because the Y chromosome is actually smaller than the X chromosome, men only have one copy of certain genes… so… if the X chromosome has a recessive allele, that has to be expressed because that is all that is there! but haploid here redundancy no redundancy diploid here but haploid here X Y Colonie High AP Biology red eye female x white eye male all red eye offspring 100% of females have red eyes x 50% of males have white eyes How is this possible? Sex-linked trait! Human X Chromosome Sex-linked usually X-linked more than 60 diseases traced to genes on X chromosome Genes on Sex Chromosomes Y chromosome SRY: sex-determining region master regulator for maleness turns on genes for production of male hormones pleiotropy! X chromosome Contains a gene called DAX1, an antitestes factor…SRY inhibits DAX1 other traits beyond sex determination hemophilia Duchenne muscular dystrophy color-blind Sex-Linked Traits HY x XHh HXh XHH Y Xh follow the X chromosomes males get their X from their mother trait is never passed from father to son Y-linked very few traits only 26 genes trait is only passed from father to son females cannot inherit trait XH XHY XH male / sperm XH XHXh Sex-Linked Traits Hints X-linked 2 ‘normal’ parents, but mother is carrier for a sex-linked trait female / eggs Explanation of Sex Linkage DeMarco/Goldberg Y XH XHXH XHY Xh XhY XHXh Colonie High AP Biology DeMarco/Goldberg Bacteria Bacteria review one-celled organisms prokaryotes reproduce by binary fission rapid growth generation every ~20 minutes 108 (100 million) colony overnight! dominant form of life on Earth incredibly diverse Bacterial Diversity Borrelia burgdorferi Treponema pallidum Lyme disease Syphillis Escherichia coli O157:H7 Hemorrhagic E. coli Binary Fission Replication of bacterial chromosome Asexual reproduction offspring genetically identical to parent where does variation come from? Enterococcus faecium skin infections Conjugation Direct transfer of DNA between 2 bacterial cells that are temporarily joined results from presence of F plasmid with F factor F for “fertility” DNA E. coli “male” extends sex pilli, attaches to female bacterium cytoplasmic bridge allows transfer of DNA