HMB265H1 Lecture Notes - Lecture 18: Sister Chromatids, Haploinsufficiency, Dna Replication

• School: UTSG
• Department: Human Biology
• Course: HMB265H1
• Professor: Naomi Levy-Strumpf, Stephen Wright

Document Summary

Polytene chromosomes & their use in studying changes in chromosome structure. Found in drosophila larvae in the salivary glands. Formed due to multiple rounds of dna replication that happened without the cells entering mitosis ; in addition, sister chromatids never separate from each other. They remained lined up and tightly associated. After many replications we can see this structure under a light microscope. Use probes & in situ hybridization to locate genes. Deletions homozygotes are usually inviable; gene imbalance in heterozygotes (haploinsufficiency) Formation of a deletion loop due to issues in pairing. Complementation test cross a del mutant to a drosophila with the recessive goi; if the progeny (del heterozygote shows the recessive phenotype, we know the goi is located somewhere within the deletion) Duplications quite frequent; less likely to affect phenotype (in some cases, there is a dosage effect/genetic imbalance and/or the genes may be placed in a new location that modifies expression)