BIO 325 Lecture Notes - Lecture 16: Operon, Histidine, Xeroderma Pigmentosum
• UV Light – can crosslink adjacent Thymines, block gene expression or DNA replication
o Must be excised and repaired
o Xeroderma pigmentosum – lack the enzyme that recognizes thymine dimers
▪ Cannor repair thymine dimes, avoid all sunlight, skin cancer
• Oxidative Damage – results in base changes
Mutations – Cannot be Repaired
• Mutatios that aot e repaired hae unequal crossing over
• Problems if there are genes with related sequences nerby on the chromosome
Mutations – Can be Repaired
• Transposons
• DNA molecules that can move from one place to another in the genome
• Reversion from mutant, wildtype can happen often
Chemicals That Increase Mutation Rate
• Mutagen
• Carcinogens – increase mutations, increase the chance for developing cancer
o Use The Aes Test to determine carcinogens
o Ames Test – used to test chemicals for their ability to cause mutations
Mutagens Induce Mutations
• Mutagens can be used to increase mutation rates
• H.J Muller – discovered that x rays increase mutation rate in fruit flies
o First induced mutagenesis
H.J Muller’s Experiet
• Exposed male Drosophila to large doses of x rays
• Mated males to females with balancer x chromosome
o Dominant Bar eyed mutation and multiple inversions
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Document Summary
Mutations cannot be repaired: mutatio(cid:374)s that (cid:272)a(cid:374)(cid:374)ot (cid:271)e repaired ha(cid:448)e (cid:862)unequal crossing over(cid:863, problems if there are genes with related sequences nerby on the chromosome. Mutations can be repaired: transposons, dna molecules that can move from one place to another in the genome, reversion from mutant, wildtype can happen often. Chemicals that increase mutation rate: mutagen, carcinogens increase mutations, increase the chance for developing cancer, use (cid:862)the a(cid:373)es test(cid:863) to determine carcinogens, ames test used to test chemicals for their ability to cause mutations. Mutagens induce mutations: mutagens can be used to increase mutation rates, h. j muller discovered that x rays increase mutation rate in fruit flies, first induced mutagenesis. Mutations and genes: mutations that cause the same phenotype are not necessarily in the same gene. Mapping mutations in the same gene: recombination occurs at random positions along the (cid:272)hro(cid:373)oso(cid:373)e su(cid:272)h as (cid:862)(cid:271)et(cid:449)ee(cid:374) ge(cid:374)es(cid:863) a(cid:374)d (cid:862)i(cid:374) ge(cid:374)es(cid:863)
