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Genetics

Genetics. Notes 3. Test Cross. How do we know if an organism that shows a dominant trait has a two dominant alleles or one dominant and one recessive allele?

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Genetics

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  1. Genetics Notes 3

  2. Test Cross How do we know if an organism that shows a dominant trait has a two dominant alleles or one dominant and one recessive allele? • A _________________ is a method for determining whether an organism that ___________________ ___________________________________________________________________________________.

  3. Test Cross • In a test cross, _________________________ _____________________________________. • If the test organism is heterozygous, ___________ ________________________________________. • If the test organism is homozygous dominant, ________________________________________. • Large numbers of offspring are necessary for valid results.

  4. Test Cross Example: • In guinea pigs, black coat color is dominant over white. How would you find out whether a black guinea pig is homozygous for coat color (BB) of heterozygous (Bb)? • __________________________________________________________________________________________________________________________.

  5. Test Cross • Using the Punnett Squares below, show the test cross described above:

  6. Multiple Alleles • So far, we have discussed traits that have only two possible alleles (Ex. Yellow/Green; Tall/Short; Round/Wrinkled), but for many genes, several alleles exist in the population. • This is called _______________________ • This expands the number of possible _____________________________

  7. Multiple Alleles Example: Multiple alleles control the character of ____________________ in humans. A person may be ______, ______, ______, or ______. • The letters refer to _______________________, called A and B, which are _____________________________ _______________________ • A persons red blood cells may be coated with _____ _____________ (A or B), ___________ (AB), or _____________ (O) • The alleles are written as • IA = _____ • IB = _____ • i = ______

  8. Multiple Alleles • Each person inherits ___________________________. • There are 6 possible ways to inherit the alleles: • _______ • _______ • _______ • _______ • _______ • O (i allele) is _________________ • A and B (IA and IB alleles) are called ________________: ______________________________ • Both carbohydrate A and B are present on red blood cells

  9. Multiple Alleles • How is this different from incomplete dominance? • ______________________________________________________________________ • Ex. ______________________________ • ___________________________________

  10. Review: Dihybrid Cross • Using the Punnett square below, work out the following cross: TTYY x TtYy

  11. Review: Dihybrid Cross • Using the Punnett square, work out the following cross: rrYy x RRyy

  12. Review: Blended Inheritance (Incomplete Dominance) Example: • Crossing pure red (RR) and pure white (WW) Japanese four-o’clock flowers results in an F1 generation in which all of the flowers are pink (RW). Show a cross between a pure red flower (RR) and a pure white flower (WW). Phenotypes:_________

  13. Review: Blended Inheritance (Incomplete Dominance) Show a cross between two members of the F1 generation (RW x RW). Phenotypes:_________

  14. Review: • What is Mendel’s law of independent assortment? • What is incomplete dominance? • What is codominance? • When do you use a test cross? • When do you use a dihybrid cross? • When do you use a monohybrid cross?

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