Genetics2 - A v e ra g e = 6 0 M a x = 9 0 .5 M in = 1 8...

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Average=60 Max=90.5 Min=18 Mendel's Dihybrid Crosses • Two Different traits in the same cross • Example: seed color and seed shape • Is the segregation pattern of one gene influenced by the segregation of another gene? ! " Answer = yes and no Depending on whether the genes are linked Spherical yellow seeds = SSYY Wrinkled green seeds = ssyy If the spherical gene is linked to yellow = SY And wrinkled is linked to green = sy l l l l S Y s y Gametes = SY sy Big S always with Big Y For linked genes:
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X sysy Gametes = SY or sy F1 = SYsy X SYsy Gametes = SY sy or SY sy F2 = SYSY SYsy sySY sysy Ratio = 3 : 1 Spherical/yellow c Sph/yellow wrinkled/green Figure 10.7 Independent Assortment For unlinked genes F1 and F2 = 4 kinds of gametes 3 possible genotypes for shape = SS Ss or ss 3 possible genotypes for color = YY Yy or yy 9 different genotypes / 4 phenotypes Law of independent assortment • Mendel’s second law, the law of independent assortment , states that alleles of different genes (e.g., Ss and Yy ) assort into gametes independently of each other. • To determine this, he used dihybrid crosses , or hybrid crosses involving additional characters. • The dihybrid SsYy produces four possible gametes that have one allele of each gene: SY, Sy, sY, and sy. • Random fertilization of gametes results in offspring with phenotypes in a 9:3:3:1 ratio. ! # Figure 10.8
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This note was uploaded on 10/08/2010 for the course MCDB MCDB 1A taught by Professor Senghuilow during the Summer '09 term at UCSB.

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Genetics2 - A v e ra g e = 6 0 M a x = 9 0 .5 M in = 1 8...

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