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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

Genetics

Notes 3

test cross
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 ___________________ ___________________________________________________________________________________.
test cross1
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.
test cross2
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)?
    • __________________________________________________________________________________________________________________________.
test cross3
Test Cross
  • Using the Punnett Squares below, show the test cross described above:
multiple alleles
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 _____________________________
multiple alleles1
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 = ______
multiple alleles2
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
multiple alleles3
Multiple Alleles
  • How is this different from incomplete dominance?
    • ______________________________________________________________________
      • Ex. ______________________________
    • ___________________________________
review dihybrid cross
Review: Dihybrid Cross
  • Using the Punnett square below, work out the following cross:

TTYY x TtYy

review dihybrid cross1
Review: Dihybrid Cross
  • Using the Punnett square, work out the following cross:

rrYy x RRyy

review blended inheritance incomplete dominance
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:_________

review blended inheritance incomplete dominance1
Review: Blended Inheritance (Incomplete Dominance)

Show a cross between two members of the F1 generation (RW x RW).

Phenotypes:_________

review
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?