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26genetics2-2007prin..
 

26genetics2-2007prin..

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  • He studied at the University of Vienna from 1851 to 1853 where he was influenced by a physicist who encouraged experimentation and the application of mathematics to science and a botanist who aroused Mendel’s interest in the causes of variation in plants. After the university, Mendel taught at the Brunn Modern School and lived in the local monastery. The monks at this monastery had a long tradition of interest in the breeding of plants, including peas. Around 1857, Mendel began breeding garden peas to study inheritance.
  • P = parents F = filial generation
  • In a typical breeding experiment, Mendel would cross-pollinate ( hybridize ) two contrasting, true-breeding pea varieties. The true-breeding parents are the P generation and their hybrid offspring are the F 1 generation . Mendel would then allow the F 1 hybrids to self-pollinate to produce an F 2 generation.
  • The genes that we have covered so far affect only one phenotypic character, but most genes are pleiotropic
  • 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
  • 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.

26genetics2-2007prin.. 26genetics2-2007prin.. Presentation Transcript

  • Genetics & The Work of Mendel
    • Modern genetics began in the mid-1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in peas
      • used good experimental design
      • used mathematical analysis
        • collected data & counted them
      • excellent example of scientific method
    Gregor Mendel
  • Mendel’s work
    • Bred pea plants
      • cross-pollinate true breeding parents
      • raised seed & then observed traits
      • allowed offspring to self-pollinate & observed next generation
    Pollen transferred from white flower to stigma of purple flower anthers removed all purple flowers result ? self-pollinate
  • Mendel collected data for 7 pea traits
  • Looking closer at Mendel’s work Parents X self-pollinate 2 nd generation 3:1 75% purple-flower peas 25% white-flower peas 100% 1 st generation (hybrids) 100% purple-flower peas true-breeding purple-flower peas true-breeding white-flower peas
  • What did Mendel’s findings mean?
    • Some traits mask others
      • purple & white flower colors are separate traits that do not blend
        • purple x white ≠ light purple
        • purple masked white
      • dominant allele
        • functional protein
          • affects characteristic
        • masks other alleles
      • recessive allele
        • no noticeable effect
        • allele makes a non-functioning protein
    homologous chromosomes I’ll speak for both of u s! allele producing functional protein mutant allele malfunctioning protein
  • Genotype vs. phenotype
    • Difference between how an organism “looks” & its genetics
      • phenotype
        • description of an organism’s trait
      • genotype
        • description of an organism’s genetic makeup
    Explain Mendel’s results using … dominant & recessive … phenotype & genotype F 1 P X purple white all purple
  • Making crosses
    • Can represent alleles as letters
      • flower color alleles  P or p
      • true-breeding purple-flower peas  PP
      • true-breeding white-flower peas  pp
    P p PP x pp F 1 P X purple white all purple
  • Punnett squares
    • P p x P p
    3:1 1:2:1 % genotype % phenotype PP P p P p pp 1 st generation (hybrids) Aaaaah, phenotype & genotype can have different ratios P p male / sperm P p female / eggs PP 75% 25% 25% 50% 25% pp P p P p
  • Any Questions??
  • Beyond Mendel’s Laws of Inheritance
  • Extending Mendelian genetics
    • Mendel worked with a simple system
      • peas are genetically simple
      • most traits are controlled by single gene
      • each gene has only 2 version
        • 1 completely dominant ( A )
        • 1 recessive ( a )
    • But its usually not that simple!
  • Incomplete dominance
    • Hybrids have “in-between” appearance
      • RR = red flowers
      • rr = white flowers
      • Rr = pink flowers
        • make 50% less color
    RR Rr rr  RR  WW  RW
  • Incomplete dominance true-breeding red flowers true-breeding white flowers X P self-pollinate 100% 100% pink flowers 1 st generation (hybrids) 25% white 2 nd generation 25% red 1:2:1 50% pink
  • Incomplete dominance
    • RW x RW
    1:2:1 1:2:1 % genotype % phenotype R W male / sperm R W female / eggs 25% 25% 50% 25% RR RW RW WW 25% 50%
  • Codominance
    • Equal dominance
      • human ABO blood groups
      • 3 version
        • A, B, i
        • A & B alleles are codominant
        • both A & B alleles are dominant over i allele
      • the genes code for different sugars on the surface of red blood cells
        • “ name tag” of red blood cell
  • Genetics of Blood type O AB B A pheno-type i i AB BB or B i A A or A i genotype anti-A & anti-B antibodies no antibodies anti-A antibodies anti-B antibodies antibodies in blood universal donor universal recipient __ __ donation status no antigens on surface of RBC both type A & type B antigens on surface of RBC type B antigens on surface of RBC type A antigens on surface of RBC antigen on RBC
  • Blood donation clotting clotting clotting clotting clotting clotting clotting
  • One gene: many effects
    • The genes that we have covered so far affect only one trait
    • But most genes are affect many traits
      • 1 gene affects more than 1 trait
        • dwarfism (achondroplasia)
        • gigantism (acromegaly)
  • Acromegaly: André the Giant
  • Inheritance pattern of Achondroplasia AA  Aa x aa a a A a A a A a Aa x Aa Aa aa aa Aa 50% dwarf :50% normal or 1:1 aa Aa 67% dwarf : 33% normal or 2:1 Aa
  • Many genes: one trait
    • Polygenic inheritance
      • additive effects of many genes
      • humans
        • skin color
        • height
        • weight
        • eye color
        • intelligence
        • behaviors
  • Human skin color
    • AaBbCc x AaBbCc
      • can produce a wide range of shades
      • most children = intermediate skin color
      • some can be very light & very dark
  • Albinism Johnny & Edgar Winter albino Africans melanin = universal brown color
  • OCA1 albino Bianca Knowlton
  • Coat color in other animals
    • 2 genes: E,e and B,b
      • color ( E ) or no color ( e )
      • how dark color will be: black ( B ) or brown ( b )
    E–B– E–bb eeB– eebb
    • Phenotype is controlled by both environment & genes
    Environment effect on genes Color of Hydrangea flowers is influenced by soil pH Human skin color is influenced by both genetics & environmental conditions Coat color in arctic fox influenced by heat sensitive alleles
  • Genetics of sex
    • Women & men are very different, but just a few genes create that difference
    • In mammals = 2 sex chromosomes
      • X & Y
      • 2 X chromosomes = female: XX
      • X & Y chromosome = male: XY
    X Y X X
  • Sex chromosomes
  • Sex-linked traits
    • Sex chromosomes have other genes on them, too
      • especially the X chromosome
      • hemophilia in humans
        • blood doesn’t clot
      • Duchenne muscular dystrophy in humans
        • loss of muscle control
      • red-green color blindness
        • see green & red as shades of grey
    X Y X X
  • Sex-linked traits sex-linked recessive 2 normal parents, but mother is carrier x X H Y male / sperm X H X h female / eggs X H X H X H X h X H Y X h Y X H X h X H X h X H Y Y X H X H X H X H Y X H X h X h Y HH Hh X H Y X H X h
  •  
  •  
  • Dominant ≠ most common allele
    • Because an allele is dominant does not mean…
      • it is better, or
      • it is more common
    Polydactyly dominant allele
  • Polydactyly recessive allele far more common than dominant  only 1 individual out of 500 has more than 5 fingers/toes  so 499 out of 500 people are homozygous recessive (aa) the allele for >5 fingers/toes is DOMINANT & the allele for 5 digits is recessive individuals are born with extra fingers or toes
  • Hound Dog Taylor
  • Any Questions?