Linkage - If G and R are linked then whenever you have a G...

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Linkage Genes on the same chromosome are linked. Example: Unlinked Genes G = gray body g = black (ebony) body R = red eyes r = purple eyes The diagrams below show that the locus for body color (G or g) is on a different chromosome than the locus for eye color (R or r). These two loci will assort independently to produce either GR and gr gametes or Gr and gR gametes. cross: GgRr X ggrr gametes: GR, Gr, gR, gr X gr Ratio expected: 1:1:1:1 Example: Linked Genes
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Suppose G and R are linked as shown below. If the body color and eye color loci are on the same chromosome, they will not assort independently unless crossing-over occurs frequently. In this case, GgRr can produce only two kinds of gametes: GR and gr. GgRr X ggrr gametes: GR, gr X gr If G and R are linked, then whenever you have a G, you have an R. Any gray, purple offspring
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Unformatted text preview: If G and R are linked, then whenever you have a G, you have an R. Any gray, purple offspring (G-rr) would result from crossing over because a Gr gamete is needed. Suppose out of 100 offspring, you got 46 gray, red, 46 black purple, 4 gray purple and 4 black red. Eight percent of the offspring resulted from crossing over. These offspring are recombinant . Crossing Over Crossing over is more likely to occur between genes that are far apart. The farther apart genes are, the greater the probability that crossing over will occur between them. In the example above, we had 8% crossing over. The percent of recombination (crossing over) can beused as a measure of how far apart genes are. 1% crossing over = 1 map unit....
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