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AP Biology - Genetics

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    AP Biology - Genetics AP Biology - Genetics Presentation Transcript

    • Mendelian Genetics
      Chapter 14
    • Mendel’s Pea Plants
      true-breeding plants
      P  F1  F2 generations
      Dominant, recessive alleles
      Law of Segregation of Alleles
      Law of Independent Assortment
    • Genetics Vocabulary
      Phenotype, genotype
      Homozygous, heterozygous
    • Punnett Squares
      Pea plants heterozygous for flower position and stem length (AaTt) are allowed to self-pollinate, and 400 of the resulting seeds are planted. How many offspring would be predicted to be dwarf with terminal flowers?
      (Axial flowers, A, dominant to terminal. Tall stems, T, dominant to dwarf.)
    • Test Crosses
      Cross any organism that displays the dominant trait with one that shows the recessive trait to determine if the dominant individual is homozygous dominant or heterozygous
    • Patterns of Inheritance
      Complete dominance
      Co-dominance
      Incomplete dominance
      Multiple Alleles (human blood types)
    • Patterns of Inheritance
      Quantitative characters – occur in gradations
      Polygenic inheritance
      Pleiotropy
    • Nature vs. nurture
      How many of our traits stem from non-genetic causes?
      Genotypes considered to fall within a “norm of reaction”
      Identical twins experiments
    • Pedigrees
      Allows charting of the inheritance of an allele over multiple generations
    • Inherited Disorders
      May not be evenly distributed
      Other factors
      Ex.: Sickle Cell
      Disorders can be dominant or recessive
      Rec.: cystic fibrosis
      Dom.: Acondroplasia (usually non-lethal)
    • Chromosomal inheritance
      Chapter 15
    • Law of Independent Assortment
      Proves that traits are passed on through chromosomes
    • Drosophila melanogaster
      Wild type alleles (ex. Red eyes) show by w+
      White eyes only in males!!!
    • GENETIC LINKAGE?
      Recombinant vs. parental phenotypes
      Cross (b+ b+ vg+ vg+ with (b b vg vg)
      F1 then crossed
      Higher percentage of parental phenotypes
    • Crossing Over’s effects
      Recombinants mean that linkage is not complete
    • Linkage Mapping
      Genetic maps list gene loci
      Crossing over = random; allows determination of distance between genes
    • Linkage Mapping
      Textbook figure 15.6
      Parents: red eyes, normal wings (w+ w, vg+ vg) crossed with white eyes, vestigial wings (w w, vg vg)
      760 offspring counted.
      Red, normal: 340
      White, vestigial: 318
      Red, vestigial: 49
      White, normal: 53
    • Sex determination
      Mammals: X-Y (Y determines maleness)
      Drosophila: X-0 (X-autosome ratio determines femaleness)
      Birds and fish: Z-W (W determines femaleness)
      Hive Insects: haplo-diploid (males develop from unfertilized eggs)
    • Sex-linked genes
      In humans, most found on longer X chromosome
      Males are hemizygous
      Examples: color blindness, hemophilia, MD
    • x inactivation
      One X inactivates, becomes a “Barr body”
      Random (so some cells can express different alleles)
    • nondisjunction
      Homologous chromosomes do not move apart properly
      Aneuploidy
      Trisomy (diploid 2n+1) or monosomy
    • Trisomy 21
    • nondisjunction
      Polyploidy: Complete extra/missing chromosome sets
      Often in plants (since offspring are sterile and cannot reproduce sexually)
    • Aneuploidy of sex chromosomes
      Klinefelter (XXY): sterile male with slight female characteristics
      XYY: relatively normal male
      XXX: relatively normal female
      Turner (X): sterile female