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Lecture 20

BIOC15Fall2013 Lecture 20 and Lecture 21.docx

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Biological Sciences
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Karen Williams

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BIOC15Fall2013 Lecture 20: Behaviour Genetics and Lecture 21 Drosophila locomotor activity o Ecolosion rhythm  emergence form pupa o Locomotor activity rhythm  movement o Measured locomotor activity to see if the absence of eclosion rhythm is due to the absence of the clock or just desynchronization between the flies o One sex comes out before the other and very shortly after light are on in the morning Drosophila: normal rhythm o Peaks occur around the same time each day, and about 12 hours apart o Mean locomotor activity o flies were tested individually in the locomotor-activity meter o Circardian rhythms o circardian rhythms are biological rhythms of about 24 hours – equal hours of day and night o clock genes are identified by mutations that change the period of rhythmicity hPer o human homolog of the Drosophila period gene o identification of genes influencing any human behavior is complicated by the other genetic influences, environmental influences and cultural factors o advanced sleep phase syndrome has been found to be due to an autosomal dominant mutation (circardian rhythm variant) o affected individuals are morning larks  go to sleep at 730 pm and wake up at 430am o they have a 4 hour sleep temperature and melatonin rhythm advance o attritubuted to hPer, homolog of the period gene in D. melanogasterflies and mammals per  The fruit fly circadian cycle shares three strong similarities with the mammalian: the per gene itself, CLOCK and BMAL regulation of per, and a gene called tau in hamsters and double-time (dbt) in flies, both of which encode the enzyme CKI o by reducing the phenotypic variance between each genotype and exaggerating the difference between genotypes we would have separated the population into three separate non overlappingphenotypic distributions, each characteristic of one genotype o to find a way to convert a quantitative trait into a qualitative (Mendelian) one we need to make the difference between th means of the genotypes large compared with the variation within the genotypes Example: Mouse behaviour 1 o two line of mice that breed true for two alternate behavioural phenotype o to do a norm of reaction study we must first create a group of identical individuals by repeated brother sister matings (inbreeding) o decreasing heterozygosity in inbreeding: o o it is possible to use genetically inbred model organisms to locate genes that contribute to the development of quantitative traits o genetic analysis detects genes only when there is some allelic variation QTL o genetic variation in quantitative traits is due to the segregation of alleles at several loci o even if it is impossible to individually identify all the genes segregating for a particular trait it is possible to identify the region of the genome where these quantitative trait loci (QTL) lie o o linkage disequilibrium two alleles separate together although not known to be linked o these deviations from what is expected by independent assortment of HW eq occur because of new physical linkage associations or population demographic events QTL mapping in mice o QTL for circardian rhythm of locomotor activity in mice o Inbred mouse strains B and D differing in the interval activity (t) were crossed to each other to develop 26 recombinant inbred (RI) strains o B and D RI strains also differed in large number of genetic markers (750) o o the RI lines were measured for their interval of activity (t) o a marker locus that is closely linked with a QTL will differ in its mean interval of activity fromone marker genotype to another o narrow heritability was estimated to be 55% o analysis identified a QTL at 45cM on chromosome 2 near a QTL known to be associated with wheel running o we can compare these results with the homolog, hPer2 o o the region different in patient with FASPS has the following amino acids around nucleotide 662 o 2 o there is a difference in patients with FASPS at 662 (G instead of S) o everyday data was collected about how often mice were active (their locomotor activity) o rodents are typically active at night (dark dots correspond to the night time) o mouse with serine at position 663 of mPer substituted for a Glycine have a shorter day (20.67 hours to 22 hours) compared to wildtype which is 23.7 horus Heritability of polygenic traits in humans can be studied using twins o Heritability o is a population not an individual measure o does not indicate how important genes are in influencing a character is population and environmental specific, it cannot be extrapolated from one population and set of environments to another Concordance of trait in two children raised in the same family o if the heritability is 0.0 (no variation in population) then there are no difference between MZ, DZ or unrelated by adoption (UR) o o if the heritability is 1.0, differences would be observed in MZ, DZ and UR o the extent of difference varies with the trait frequency o Heritability: Twin studies o the phenotypic correlations differing between MZ twins and DZ twins are often used in estimating heritability o MZ twins are treated more similarly than DZ twins  environment is almost identical for MZ o MZ may have greater social interaction than DZ o So environmental correlations are not the same as for identical twins as for fraternal, and heritability is overestimated 3 Is heritability fixed? o Studies have been made of he heritability of IQ p
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