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Lecture 13

HMB321H1 Lecture Notes - Lecture 13: Synteny, Gamete, Chromosome

Human Biology
Course Code
Maria Papaconstantinou

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4 MAR 2011
HMB321 L13: Linkage Genetics
Assumptions of independent assortment
-Genes are located on different chromosomes, or they are located a great distance apart
-Mendelian inheritance works if no linkage is assumed
T.H. Morgan
-Principal of linkage
-Theory of sex-linked inheritance
-Genes are linked if they were located near each other (“syntenic genes”)
Distance between genes
-The further the genes are in a chromosome, the higher the recombination frequency it has, therefore
the less linkage the two are encountering
-The closer, the higher the linkage, the less recombination (i.e. Less independent assortment)
-Refer to slides for “Distance of Recombination” calculation
Case Study
-Distance = # recombinant gametes / total of gametes x 100
-Recombining gametes = 1 out of the affected 7 with BO => 14.3% (= 14.3cM distance)
-Real answer = 10cM
-10 potentials for recombination (do not count those that married in)
-And only 1 unaffected out of 10 progeny (not those that married in) from generation 1
-Therefore = 1 unaffected (due to recombination) / 10 total progeny = 0.1 = 10.0cM
-Are normal variations in DNA sequence of 1 nucleotide
-Genetic variants that are near each other tend to be inherited together because of lower
recombination frequency (RF)
-Known SNPs are useful tools to map disease genes
-Linked region of allelic variants
-Certain people that inherit a certain amount of the same SNPs => haplotypes
-Tag SNPs identify your haplotype
-Important for mapping disease loci
HapMap Project
-International collaboration to identify human haplotypes
-Looking at different genomes via haplotypes (via tag SNPs)
Identifying Disease Genes
-Genotyping a given set of Tag SNPs in a disease population could help identify a causative gene
-May show you that a good percentage of these people share a haplotype
-Can study region around that haplotype to identify potential variants + factors affecting disease
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