5 - BIO 320 Lecture 5 Gene linkage mapping I and 2 analysis Chapter 5 5-3 5-2 5-5 5-9 5-11 5-9 QB G1 2 4-6 8 9 H1-16 29 32 34-37 39-46 2008 Gene

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Gene linkage: The concept of gene linkage was first formulated in 1905 by Bateson, Saunders and Punnett to explain non-Mendelian ratios in di-hybrid crosses in the sweet pea. The chromosomal basis for this phenomenon was established by Morgan's fly group. Segregation of these two chromosomes (without recombination) generates two classes of gametes (and therefore two phenotypic classes of progeny): Consider the gametes from a female heterozygous for white and minature : w m w + m + X test-cross mating with a white, minature male. MALE GAMETES: w m Y w m or Y w m w m + + w m + + w m + + w m w m w m w m Y Y BUT, occurrence of both w m + , and w + m progeny indicatesthat recombinant X- chromosomeshave been produced during meisosisin these females w m w m + + Recombinant chromosome in red-eyed progeny with minature body size. Recombinant chromosome in white-eyed progeny with normal body size. In this example with w and m, 37% (900/2441) of the F2 progeny are 'recombinant' for these two genes (versus 0% if always linked and 50% if unlinked). These two genes are separated by 37 map-units, or centimorgans. BIO 320: Lecture 5 χ 2 analysis. w = recessive white mutation, (white eye phenotype) w + = dominant wild-type allele, (red eyes) m = recessive minature mutation, (small body size) m + = dominant wild-type allele, (normal body size) e.g. -linkage of white and minature (two sex-linked genes): Conclude: 1). white and minature are linked 2). genes that are linked do not always co-segregate in meiosis, i.e. there is recombination between linked genes!! red, normal white, minature white, normal red, minature 791 750 455 445 2441 Parental Recombinant white eyes, minature body red eyes, normal body X w w m m + w m X w m w + m + w + m + If the w and m genes assort independently, then there should be a
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This note was uploaded on 06/03/2008 for the course BIO 320 taught by Professor N/a during the Spring '08 term at SUNY Stony Brook.

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5 - BIO 320 Lecture 5 Gene linkage mapping I and 2 analysis Chapter 5 5-3 5-2 5-5 5-9 5-11 5-9 QB G1 2 4-6 8 9 H1-16 29 32 34-37 39-46 2008 Gene

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