Genetic linkage Flashcards
What is linkage analysis?
A method that is used in establishing the carrier
status of female ‘at-risk’ and for prenatal diagnosis.
What is the principle of independent assortment?
The alleles on different chromosomes are distributed randomly
(OR independently assorted) of each other to individual gametes. thus, genes are NOT linked
What are recombinant gametes?
New combination of alleles generated
from recombination
Define the coupling phase (cis)
when the dominant A and B alleles (test alleles/markers) are on the same chromosome
Linkage phase is written as: AB/ab
Define repulsion phase (trans)
when the dominant A and B allele are on the homologous
chromosomes
Linkage phase is written as: Ab/aB
How will the gametes be arranged if A and B alleles are in coupling phase?
Majority of the gametes will have either two dominant
alleles or two recessive alleles on the same
chromosome.
How will the gametes be arranged if A and B alleles are in repulsion phase?
Gametes containing one dominant and one recessive
allele will be most abundant.
How would knowing the linkage phase help a geneticist?
In clinical setting, knowing the linkage phase would allow geneticists to predict the risk of a couple to produce an “affected” child
What is recombination frequency?
The proportion of recombinant gametes produced varies depending on how often crossovers occur between the two genes.
It can be calculated as No.of recombinant progeny/total progeny * 100
What is Map distance?
This is the percentage of recombinant offspring produced based off the distance between two genes
what is 1 map unit?
Distance between two loci that will generate 1% recombinant phenotype between them
E.g 12% recombination = 12mu
What are the limitations of a 2 point test cross?
Difficult to determine gene order if two genes are too close or too
far apart
Actual distances between genes do not always add up (double
crossing-overs, COs)
Pairwise (test) crosses are time and labor consuming, not
amenable for all species
What are the advantages of a 3 point tests cross?
Faster and more accurate way to map
genes
Simultaneous analysis of three markers
Information on the position of three genes
relative to each other can be obtained
from one mating rather than two
independent matings.
Being able to include double crossovers
is the reason three point crosses are
more accurate than two point crosses
