HMB265H1 Lecture Notes - Lecture 22: Sister Chromatids, Chromosomal Inversion, Haploinsufficiency

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HMB265 Lecture 18 changes in chromosome structure
Chromosomal mutations
- Relocation of genetic material
o Translocation
o Inversion
- Loss of genetic material
o Deletion
o Missing chromosomes
- Gain of genetic material
o Extra chromosome
o Duplication
Polytene chromosomes are used to study changes in chromosome structure
- Drosophila
- During meiosis the sister chromatids remain associated
- After many round we can see the macromolecule under the microscope
- This allows us to locate genes on the chromosome and see how the chromosomes have
changed
Deletions
- Result from things that introduce double-stranded breaks in DNA
- Intragenic small deletion within gene
- Multigenic: many genes deleted all at once
o Del homozygotes are inviable
o Gene imbalance in Del heterozygotes
Might results in haploinsufficiency
In some cases, for certain genes it can result in unviability
- Deletion loop part of the chromosome is deleted in the form of a deletion loop
o can be seen under the microscope
Pseudodominance
- Deletion uncovers the mutant gene
- Shows dominance but it is not actually dominant
- Deletions can be used to locate genes = mapping
Deletion mapping: complementation
- In complementation tests we cross a deletion mutant with the mutant gene of interest
- The Del heterozygote reveals the location of mutant gene
- Very powerful technique and rather quick and easy
Duplication
- Less likely to affect the phenotype
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