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Codominance + Multiple Alleles

Codominance + Multiple Alleles . So far = traits involve only two alleles per gene but f or most genes, more than two alleles exist For example: Blood Types in Humans A person can have one of four blood types: A, B, AB, or O Each letter refers to two types of carbohydrates (A or B)

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Codominance + Multiple Alleles

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  1. Codominance + Multiple Alleles • So far = traits involve only two alleles per gene butfor most genes, more than two alleles exist • For example: Blood Types in Humans • A person can have one of four blood types: A, B, AB, or O • Each letter refers to two types of carbohydrates (A or B) • Why is it critical to match blood types?

  2. Antigen: Cell parts that produce an immune response. Eg. identification proteins on Red blood cells (RBC) • Antibody: Proteins that react to antigens. Eg B antibody reacts to B antigen

  3. Blood Types in Humans • Type A • Type B • Type AB • Type O • Complete handout

  4. Chromosome Theory of Inheritance • Genes are located at specific positions on chromosomes • Segregation and assortment of these chromosomes during meiosis is responsible for inheritance patterns

  5. Sex-Linked Traits A trait controlled by the genes on a sex chromosome Discovered by Thomas Hunt Morgan (early 1900s) while studying inheritance of white eye colour in fruit flies In humans, most sex-linked genes are found on X chromosome (X-linked)

  6. Y-linked disorders • Although many sex-linked genes are located on X chromosome, some genes are located on Y chromosome (passed down from father) • Y-linked disorders caused by mutations in genes located on Y chromosome • Y-linked traits, whose allele is carried on Y chromosome often leads to sterility (can not be inherited) For example: SRY (sex-determining region) ortooth enamel formation

  7. Conditions necessary to see sex-linked traits: *a) no corresponding gene on Y chromosome b) trait (gene) appears on X and Y chromosome c) no corresponding gene on X chromosome

  8. Some sex-linked traits • Red/Green Colour Blindness(recessive, on the X chromosome) B = Normal vision and b = red/green colour blind XX XY  XBXB Normal XBY- Normal XbXb Red/green colour blind XbY- Red/green XBXb Carrier colour blind

  9. The test to the left is simpler. The individual with normal color vision will see a 5 revealed in the dot pattern. An individual with Red/Green (the most common) color blindness will see a 2 revealed in the dots.

  10. Hemophilia(recessive, on the X chromosome) • 1 in 10 000 babies (predominately boys) XhXhXhY H = normal blood clotting h = hemophilia(bleeder's disease) • Muscular Distrophy(recessive, on the X chromosome) XdXdXdYD = normal muscles d = muscular dystrophy (progressive weak muscles)

  11. 50% males colour blind  25% children colour blind • 50% females carriers

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