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Genetics Notes 3
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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 ___________________ ___________________________________________________________________________________.
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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.
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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)? __________________________________________________________________________________________________________________________.
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Test Cross Using the Punnett Squares below, show the test cross described above:
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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 _____________________________
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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 = ______
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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
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Multiple Alleles How is this different from incomplete dominance?
______________________________________________________________________ Ex. ______________________________ ___________________________________
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Genotype Phenotype ii IAIA IAi IBIB IBi IAIB
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Review: Dihybrid Cross
Using the Punnett square below, work out the following cross: TTYY x TtYy
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Review: Dihybrid Cross
Using the Punnett square, work out the following cross: rrYy x RRyy
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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:_________
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Review: Blended Inheritance (Incomplete Dominance)
Show a cross between two members of the F1 generation (RW x RW). Phenotypes:_________
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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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