2H- Gene mapping and cloning Flashcards
What is Genetic mapping?
the frequency of meiotic crossovers between loci (specific location of a gene or DNA sequence on a chromosome) is used to estimate distances between loci.
What is physical mapping?
involves using cytogenetic, molecular, and computational methods to determine the actual physical locations of disease-causing mutations on chromosomes.
What are “linked” genes?
genes located near one another on the same chromosome are transmitted together rather than independently.
What is a haplotype?
a combination of alleles at adjacent locations on a chromosome that are transmitted together.
What is recombination?
new rearrangements of alleles. Crossover does not always lead to recombination because a double crossover can occur between two loci, resulting in no recombination.
What is a Centimorgan?
a unit of measure for distance between two loci. One cM (centimorgan) is approximately equal to a recombination frequency of 1%.
What is Syntenic?
Loci that are on the same chromosome.
How far apart must syntenic chromsomes be to be unlinked?
50 cM
What is the linkage phase?
the arrangement of alleles of linked loci on each chromosome
What are markers?
polymorphisms that are used as “markers” to follow a chromosome with a disease-causing allele.
What is a Recombination hot spot?
regions where recombination frequency is at least 10-fold higher than anywhere else on the chromosome.
What is Uninformative mating?
a mating generation in which it is impossible to determine linkage phase.
What is Functional cloning?
the use of a gene product and its function to pinpoint the gene.
What is positional cloning?
locating a disease-causing gene by starting with a known linked marker near the gene of interest and then searching around that region to find it.
What are Artificial chromosomes (YACs, BACs, PACs)?
DNA is partially digested with restriction enzymes to produce overlapping fragments. These fragments are then cloned into vectors such as YACs, BACs, and PACs using recombinant DNA techniques
What is a contig map?
a physical map of a chromosome region constructed by isolating overlapping (contiguous) DNA segments.
What are Sequence tagged sites (STSs)?
Their chromosome location has been established, making them useful as indicators of physical positions on the genome
What are Expressed sequence tags (ESTs)?
Since they are derived from cDNA libraries, these small sequences represent portions of expressed genes.
What is a Chromosome-specific library?
a library that consists mostly of DNA from only one chromosome because it is created by using flow cytometry to separate chromosomes according to the fraction of AT base pairs in each one
What are CG islands?
About 60% of human genes are unmethylated CG dinucleotides found near the 5’ end.
What is Exon trapping?
method for isolating exons by using an in vitro cell system to artificially splice out the introns.
What is a linkage map?
a genetic map that shows the relative positions of known markers in terms of recombination frequency
How can you measure distance on a linkage map?
distance can be approximated by using recombination frequency: each % of recombination frequency is approximately 1 cM in distance.
What is the purpose of a likelihood ratio and LOD score?
to determine whether or not the results of a linkage study is due to chance
What is the LOD equation?
LOD score = log10(likelihood linked/likelihood unlinked). If the LOD score is 3.0 or more, it shows that there is linkage
What are important about Highly polymorphic loci?
Highly polymorphic markers will ensure that most parents will be heterozygous for the marker locus, allowing a linkage phase in families to be established. Without highly polymorphic markers, the mating will most likely be considered uninformative.
What is association?
the co-occurrence of two traits or events more often than expected by chance.
What is linkage equilibrium?
lack of preferential association of alleles at linked loci.
What is linkage disequilibrium?
a nonrandom association of alleles at linked loci in populations.
What is the relationship between haplotype and equilibrium?
If the actual frequency of a haplotype is the same as the predicted, there is statistical independence there is linkage equilibrium. If the actual frequency deviated from the predicted, then there is linkage disequilibrium
What is the main difference between loci and association?
Linkage is the position of the loci on the CHROMOSOMES. Association is the relationship between 2 traits in the general POPULATION.
What does deletions show in gene mapping?
the localization of a disease-causing gene
How can you use translocation in gene mapping?
It works by obtaining two patients with the disease with balanced translocations between one shared chromosome (the one in which the disease lies) and one different one. By analyzing the breakpoints of the translocations on the shared chromosome, a more refined location can be obtained.
What is a candidate gene?
A candidate gene is a gene with a known protein product that makes it a likely candidate for causing a specific genetic disease
