Lecture 20 Bio325 Fall 07

Lecture 20 Bio325 Fall 07 - Chromosomal Rearrangements Rare...

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1 Chromosomal Rearrangements: Rare, but can occur during meiotic recombination, mitotic recombination, or as a result of replication errors or repair of DNA damage Table 14.1 Deletions : a cell that is heterozygous for a deletion will form a deletion loop during prophase of meiosis I; no recombination can occur within the looped out region a deletion paired with a recessive mutation in the same region in a heterozygote will allow the normally recessive mutant phenotype to be expressed (“pseudodominance”) thus the location of specific mutations can be mapped by crossing the mutants with different deletion mutants Fig. 14.4, 14.5, 14.8
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2 Generation of deletions and duplications often occurs during recombination by mispairing of repeated sequences Fig. 14.13 Generation of inversions can also occur during recombination between inverted repeats, or by repair of DNA damage Fig. 14.14 Inversions that include the centromere are pericentric meiotic recombination events involving inversion chromosomes are rarely viable because they result in loss of genomic regions in the gametes Fig. 14.16
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3 Inversions that do not include the centromere are paracentric meiotic recombination involving a paracentric inversion results in a dicentric (2 centromeres on a single chromosome) product in addition to an acentric (no centromere) product. The dicentric chromosome is usually broken during cell division and the acentric chromosome is lost Fig. 14.16 Two yeast strains were mated and sporulated (allowed to carry out meiosis). One strain was a haploid with normal chromosomes and the linked genetic markers ura3 and arg9 on either side of the centromere. The other strain was wild-type for the two markers but had an inversion in this region of the chromosome (pink) as shown:
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Lecture 20 Bio325 Fall 07 - Chromosomal Rearrangements Rare...

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