04BIS10110152013RecombinLect4

In the dihybrid cross shown above a 1111 ratio of rryy

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Unformatted text preview: geny with the homozygous recessive parent. homozygous For a monohybrid cross, the test cross progeny exhibit a 1:1 ratio of Rr Rr and rr. In the dihybrid cross shown above, a 1:1:1:1 ratio of RrYy; Rryy; rr In rrYy; rryy is obtained. is RY ry Ry rY ry RrYy Rryy rrYy rryy 1: 1:1:1 (this ratio occur only with “unlinked” genes) (this “unlinked BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 4 Key Mapping Concepts Genetic linkage: Unlike Mendel's experiments, genes can be linked Unlike to each other on the same chromosome. If two genes are close together on the same chromosome pair, they do not assort independently. independently. ­Genetic distance: The distance between gene loci on a chromosome The can be measured in terms of the recombination frequency ( RF), can ), produced by crossing over between two loci during meiosis. Roughly, 1% recombination equals 1 map unit (m.u.) for short distances (e.g., 1% to 15% RF). ­Gene order and the 3 factor cross (trihybrid cross) : Interlocus map factor Interlocus distances based on recombination measurements are roughly additive and can be used to determine gene order. and ­Interference: One crossover can influence the occurrence of a One second crossover in an adjacent region. Interference distorts map distances. distances. ­Mapping function: For recombination frequencies (RF) larger than For 15%, the 1 to 1 relationship between RF and m.u. breaks down. For example, an RF of 27.5% actually equals 40 m.u. example, ­ BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 5 Gene Linkage All of the genes on a single chromosome are inherited as a group (linkage group); that is, during cell division they act and move as a unit rather than independently. The existence of linkage groups explains another exception to Mendel’s findings (i.e, Law of Independent A...
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This note was uploaded on 02/12/2014 for the course BIS 101 taught by Professor Simonchan during the Spring '08 term at UC Davis.

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