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Genetics 3 other traits ib

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  • 1. Beyond Dominant and Recessive Alleles Co – Dominance Multiple Alleles Sex – linkage and Traits Polygenic Traits
  • 2. New Concepts
    • Some alleles are neither dominant nor recessive.
    • Many genes have more than two alleles.
    • If a gene is located on the X chromosome (sex-linked), females will have two alleles, but males will only have one.
  • 3. Co Dominance – Type I
    • Occurs when one allele is not completely dominant over the other
    • The heterozygous phenotype is a blending of the two homozygous phenotypes….results in a NEW phenotype
  • 4. Example of incomplete dominance: flower color in snapdragon plants
  • 5. Another example of incomplete dominance – horse color
  • 6. Co-Dominance – Type II
    • Both alleles contribute to the phenotype
    • Instead of a blend, phenotype shows distinct features of both alleles – NO NEW PHENOTYPE
  • 7. Example of Co dominance
    • Feather color in chickens
    • Two alleles: F B = Black
            • F W = White
    • Heterozygous phenotype shows a black – white speckled feather
  • 8. Example of Co dominance:
  • 9.  
  • 10. Multiple Alleles
    • Many genes have more than two alleles!
    • Does not mean an individual can have more than two alleles
    • Only means there are more than two possible alleles in the population.
  • 11. Multiple Alleles and CoDominance
    • Human blood typing:
      • Multiple allele: A, B, O
      • CoDominace: AB blood type
  • 12. Possible genotypes and phenotypes
    • Genotype Phenotype
  • 13. Sex-Linkage
    • Coded for by genes on the X chromosome. THERE ARE NO TRAITS FOUND ON THE Y CHROMOSOME.
    • Females have two X chromosomes, so have two alleles for the gene
    • Males have one X (and one Y, which doesn’t have the same genes as an X), so males only have one allele for the gene.
    • Colorblindness & Hemophilia – recessive trait on X chromosome
  • 14. Red-green color-blindness: an example of a sex-linked trait
    • Two possible alleles
      • X C - normal (dominant)
      • X c - color blind (recessive)
      • SAMPLE EXAMPLES:
  • 15.  
  • 16. Possible genotypes and phenotypes
    • Genotype Phenotype
  • 17.  
  • 18. Some Sex linked Traits
    • Colorblindness – Red and Green**
    • Hemophilia**
    • Some Muscular Dystrophies
    • Some Respiratory Enzyme Deficiencies
  • 19. Polygenic Traits
    • Traits such as height, weight, and skin color result from the cumulative effects of many genes.
    • These traits are not expressed as “either/or’” as was the case with Mendel’s pea plant traits.
  • 20. Polygenic Traits, cont’d
    • Recognizable by their expression as a gradation of small differences (a continuous variation).
    • Resulting phenotypes form a bell-shape curve.