GENE20001 Lecture Notes - Lecture 4: Restriction Fragment Length Polymorphism, Restriction Digest, Indel
Three-point testcrosses inform gene order and genetic distance
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Consistency in gene order and genetic distance
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Stable gene location
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Linear arrangement of genes along a chromosome (beads on a string)
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Frequencies of crossing over is proportional to distance between genes
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Positional cloning: finding the position of a chromosome by conducting crosses.
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We can combine data from different experiments to form a chromosome map. e.g. building a
chromosome map by combining results from multiple three-factor crosses
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Building a chromosome map
Phenotypic mutants are rare - not ideal for building high-density map
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Phenotypic differences not always clear-cut
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Multiple genes might affect same phenotype
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Dominance
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Need to maintain mutant stocks → labour intensive → costly
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Low throughput → time consuming
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Limitations of phenotypic markers
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Genetic markers
Differences in DNA sequence
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Differences in charge of proteins (not covered)
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Molecular: they are DNA polymorphisms. Can also refer to differences in proteins
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Phenotypic vs molecular markers
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Molecular markers
4 Chromosome maps and markers
Sunday, 9 March 2014
12:41 AM
Genetics Page 1
Document Summary
Three-point testcrosses inform gene order and genetic distance. Linear arrangement of genes along a chromosome (beads on a string) Frequencies of crossing over is proportional to distance between genes. We can combine data from different experiments to form a chromosome map. e. g. building a chromosome map by combining results from multiple three-factor crosses. Positional cloning: finding the position of a chromosome by conducting crosses. Phenotypic mutants are rare - not ideal for building high-density map. Need to (cid:373)ai(cid:374)tai(cid:374) (cid:373)uta(cid:374)t sto(cid:272)ks la(cid:271)our i(cid:374)te(cid:374)si(cid:448)e (cid:272)ostly. Conceptually similar to phenotypic markers - both tag and track chromosome transmission. Difference in scoring variations: phenotypic markers scored by visual inspection; molecular markers scored by chemical assays. Many markers can be scored (=genotyped) in a single cross: one pedigree can score many markers. Genotyping can be automated and streamlined: cost effective. Southern blot e. g. use hindiii restriction enzyme to restriction digest dna into many fragments of different sizes. Rflp detects restriction site variation and insertion/deletion polymorphism.
