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Lecture 7

CAS BI 216 Lecture 7: Genetics - Lecture 7 (2/16/17)

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CAS BI 216
John Celenza

Lecture 7 – 2/16/17 – Chapter 7 § Linkage o genes mapped in small units - overlapping maps -> greater § can never see beyond 50 mu (only 50% recombination) o Possible Meiosis events § 0% - everyone is parental § SCO (50%) - like the middle § DCO - 0% Recombinants (look like parents § DCO 3 strans - two different strands recombine with one (both sets of 2 can do this to the 3rd) - 50% recombinance § DCO 4- strand - 100% § triple crossovers -> get to 50 % o genetic maps can understimate physical distance between genes § no longer doing tetrad analysis Chapter 7 - Mutations 7.1 Mutations: Primary Tools § geneticists like mutants o they have to figure out how many different genes have been mutagenized o A+ -> a (mutation is recessive); b+ -> B (mutation is dominant) o mutation needs to show phenotypic difference to be detected § forward mutation - more common; wt -> mutant allele § reverse mutation - less common; mutant allele -> wt § complementation - mutant alleles must be recessive to WT allele o do two mutants with same phenotype have mutations in two different genes or in same gene? § types of mutations - substitution, deletion, insertion, inversion - reads backward o substitution occurs at a very low rate - app. every 3-20 human gametes § depends on size (larger genes -> more mutations) § susceptibility (some genes prone to mutate) 7.3 - What Mutations Tell Us About Gene Structure § unlinked and same mutant phenotype (aa BB = AA bb) o example of complementary genes - hearing in AaBb § dominant mutant allele - will not complement § if they are recessive and unlinked - compliment § if they are in the same gene - fail to compliment § eye color mutations - all alleles of one gene or mutations in different genes o 9 color mutants - cross with the other 9 § look at phenotype of dihybrid o if it looks like WT = +; mutant = - o crosses between same mutations => have same mutation (failure to compliment) § they will be on the same gene; assuming they are recessive o garnet ruby and vermillion x white => have mutat
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