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Dominance and Multiple Allele Notes

Dominance and Multiple Allele Notes. Mendel’s Principles – A Review. Inheritance of traits is determined by genes. Genes are passed from parents to offspring. Alleles can be dominant or recessive.

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Dominance and Multiple Allele Notes

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  1. Dominance and Multiple Allele Notes

  2. Mendel’s Principles – A Review • Inheritance of traits is determined by genes. • Genes are passed from parents to offspring. • Alleles can be dominant or recessive. • In sexually reproducing organisms – each adult has two copies of each gene – one from each parent.

  3. Exceptions to Mendel’s Work • Some alleles are neither dominant or recessive. • Many traits are controlled by multiple alleles or multiple genes.

  4. Genetic Interactions Incomplete dominance – When the alleles are blended and the offspring have a mix of their parent traits. ex. Snap Dragons RR = Red WW =White Offspring can be pink!

  5. Genetic Interactions Codominance – In this case both alleles are expressed. BB= black corn YY= yellow corn BY = black and yellow corn Heterozygous genotype

  6. Incomplete Dominance or Codominance?

  7. Incomplete Dominance or Codominance?

  8. Incomplete or Codominance?

  9. Polygenic Traits • A polygenic trait is determined by multiple genes. (poly=many, genic=genes) Example: eye color and height Skin color is controlled by more than four genes

  10. Multiple Alleles Homologous chromosomes - Chromosomes occur inpairs. (homologous means “same”) - The different alleles of a gene occupy the same positionson each chromosome

  11. Multiple Alleles So far each gene we have discussed has been made of two possible alleles. Ex. B = blue b= yellow R = red r = white

  12. Multiple Alleles However, it is possible to have several different allele possibilities for one gene. Multiple alleles is when there are more than two allele possibilities for a gene. Coat color in rabbits is determined by a single gene with 4 possible alleles.

  13. Multiple Alleles In traits with multiple alleles, each individual can carry any two of the several possible alleles. Ex. BLOOD TYPE The gene for blood type has 3 possible alleles. IA, IB, and i

  14. Blood Type In this case both A and B are dominant to O (recessive). A and B are codominant (both expressed) So... there are four human blood types

  15. Multiple Alleles Alleles for blood type are: -IA (dominant) -IB (dominant) -i (recessive)

  16. Blood Type Practice Problems: 1. A mother is AB and a father is O. Draw the punnett square. IA IB i i What is the probability their offspring will have A type blood? ____ Can they have an offspring with O blood? ____

  17. Blood Type 2. A mother is IAi and a father is IB IB. Draw the punnett square. What is the probability their offspring will have B type blood? Can they have an offspring with O blood?

  18. Blood Type 3. If a child has AB blood which of the following could NOT be the parents? a) ii, IAIB b) IAi, IBIB c) IBIB, IAIA d) IAi, IBi

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