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Genetic Crosses
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Genetic Crosses


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  • 1. Genetic Crosses
  • 2. Incomplete Dominance
    • One allele for a trait is not dominant over the other
    • Heterozygous condition produces a phenotype that is intermediate of the two alleles
    • Use capital form of two different letters
  • 3. Incomplete Dominance Red Snaps White Snaps RR WW RW All Pink RW X RW
  • 4. Codominance
    • One allele for a trait is not dominant over the other
    • The heterozygous condition produces a phenotype in which both variations appear
  • 5. Codominance
  • 6. Try these two
    • In cats when a long tailed cat is bred with a no tailed cats short tailed cats are produced. If a short tailed cat was bred with a no tailed cat, what is the likelihood that a short tailed cat would be produced? Is this incomplete or codominance?
    • 2) Also in cats a black haired cat and a white haired cat produce a tuxedo (mix of black and white). If a two tuxedo cats were bred, what would be the likelihood of producing a white cat? Is this incomplete or codominance.
  • 7. Sex-Linked Traits Activity Hemophiliac Male X h Y Normal Male X H Y Hemophiliac Female X h X h Carrier Female X H X h Normal Female X H X H Overall Total Group Total Phenotype Genotype
  • 8. Sex Linked Traits
    • Traits that have a gene (allele) located on a sex-chromosome. Most traits the gene is located on the X chromosome
    • Since males have only one of two X chromosomes they only need one recessive gene to carry the trait.
    • Must include sex chromosome in cross
    • Examples are colorblindness and hemophilia
  • 9. Colorblindness Test
  • 10. Sex-linked Trait example
    • Normal vision is dominant to colorblindness. A heterozygous (carrier) female marries a normal male.
  • 11. 3-2-1 Think about
    • List 3 human traits that seem to have a range of possible variations (rather than simply 2 or even 3 distinct variations)
    • Describe 2 reasons why you think traits could have a range of variations
    • Give one definition for the word POLYGENIC
  • 12. Polygenic Traits
    • Traits controlled by more than one gene.
    • Usually creates a range of variations possible
    • Examples: Eye color, skin color, hair color, height
    • See Child/Grandchild lab for examples
  • 13. Answer the following
    • How similar or different does your child look compared to you in terms of hair, eye, or skin color?
    • How could the genotypes of the child change to make them look more/less similar than you?
  • 14. Multiple Alleles
    • More than two alleles (gene variations) for a trait.
    • Example A B O blood types
  • 15. Blood Type Donate /Receive ii O I A I B AB I B I B I B i B I A I A I A i A Antibody for: Antigen on Blood Genotype Blood Type
  • 16. Blood Type Examples
    • A woman with O blood and man with A blood marry. Could they have a child with O blood? Could it be possible that there is no chance of having children with O blood?
    • A man with B blood marries a woman with AB blood. They have a child with A blood. What has to be dads genotype? Prove it.
    • A man with A blood (I A I A ) and woman with B blood (I B I B ) have a child. The child needs a blood transfusion. Do they need to worry about the child getting the wrong type of blood? Why or why not?