lect5 - Lecture5 1...

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1 Lecture 5
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2 Linked genes, recombination, and chromosomal mapping Mendel's Law of Independent Assortment is a consequence of the  fact that chromosomes segregate independently in meiosis These results are readily explained by the two alternative ways the chromosomes can line up on the metaphase plate during meiosis I: Take two individuals One heterozygous and one homozygous AaBb x aabb
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3 MeiosisI These results are readily explained by the two alternative ways the chromosomes can line up on the metaphase plate during meiosis I: A a B b OR A a b B AB ab Ab aB Because the A and B genes assort independently, AaBb dihybrids constructed from different parental genotypes will behave the same. AABBxaabb AAbbxaaBB
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4 AaBb x aabb AABB x aabb AAbb x aaBB AaBb x aabb A a B b AaBb OR
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5 Why 50:50 Why not 25:25:25:25 A dihybrid cross involving the genes A and C produced the following results: A= Tall a= short  C= Cream  c = white   Cross I: Cross II:
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6 In these crosses, independent assortment is not occurring. For example in the first cross, the alleles Tall and Cream behave as if they are linked to one another. Similarly in the second cross the alleles Tall and white appear as if they are linked to one another. These results are readily explained if the genes A and C lie next to one another on a chromosome:
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7 Cross I: A= Tall a= short  C= Cream  c = white A-C A-C a-c a-c A-C a-c a-c a-c
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8 Cross II: A= Tall a= short  C= Cream  c = white A-c A-c a-C a-C A-c a-C a-c a-c
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This note was uploaded on 09/15/2011 for the course BIO 105 taught by Professor Sullivan during the Winter '08 term at UCSC.

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lect5 - Lecture5 1...

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