Linkage and genetic Mapping part 1
(No more Mendelian genetics)
Genetic linkage is the tendency of genes that are located proximal to each other on a chromosome to
be inherited together during meiosis. Genes whose loci are nearer to each other are less likely to be
separated onto different chromatids during chromosomal crossover, and are therefore said to be
Mendel just so happened to be lucky (7 pairs of chromosomes, 7 traits). Or he cheated, but a good
Recall: octands wt dyhibrid cross, you would expect 4 octad types (4 gamete types, in equal
proportions in each)--->he fixed the slide by adding 2 columns
NEMJ case study:
The case discussed is a form of dementia (most common form of dementia=alzheimers, but there
are other kinds as wel). This was not alzheimers. Huntington's disease is another kind of dementia.
Doc thought it was huntingtons disease, but a TEST FOR EXPANDED TRINUCLEOTIDE
REPEAT IN HUNTINGTON'S GENE CAME OUT NEGATIVE
These tests come from genetic mapping, we are able to locate these genes because weve mapped it.
Gene coding for protein called Huntingtin, in pts that have the disease there is a lot more CAG
repeats than in normal functioning person.
Huntington, by the pedigree given, appears to be a dominant disease.
To do genetic mapping, we look at what we know already, we have some genetic markers.
See the RFLP next page...The main difference between affected and unaffected is the band at 4.9
kb. This band can be associated with a phenotype of having Huntingtons.
This kind of test helps us narrowing where exactly the genomic region is, wtin a 100 thousand bps.
Ask some questions, find the gene, and now we have a test (use PCR)
At this stage, most of the diseases that afflict us are not diseases link Huntingons. They are complex
diseases, that are MULTI-FACTORAL, many different genes responsible for the trait.Aren't
explicitly as easy to track as hemophilia or Huntingtons.
Parentals=resemble the parents genotypically, recombinants, do not
When there is linkage, we expect more of the progeny to resemble the parents.