linkage 1,2- lecture 12,13 Flashcards
linkage
The tendency for genes or segments of DNA closely positioned along a chromosome to segregate together at meiosis, and therefore be inherited together
(opposite of independent assortment)
Manhattan plot
A Manhattan plot, which plots the association statistical significance as –log10(p-value) in the y-axis against chromosomes in the x-axis, is a good way of displaying millions of genetic variants in one figure. One can easily spot regions of the genome that cross a particular significance threshold
x linked genes
men inherit baldness from their maternal lineage
sex influenced autosomal trait
(dominant in males and recessive in females) or vice versa, differently expressed due to hormonal environments
centimorgan
A centimorgan (abbreviated cM) is a unit of measure for the frequency of genetic recombination. One centimorgan is equal to a 1% chance that two markers on a chromosome will become separated from one another due to a recombination event durin g meiosis (which occurs during the formation of egg and sperm cells).
recombinant frequency
number of recombinant progeny/total number of progeny *100
recombination
Genetic recombination is the exchange of genetic material between different organisms which leads to production of offspring with combinations of traits that differ from those found in either parent
genetic maps reflect distance based on how
often, on average, recombination occurs between two loci. The further
apart two loci are the higher the chance that a crossing over will take
place and thus the greater the genetic distance between them.
Conversely, if two loci are located very close together, there is very little
chance for crossing over to take place. Thus, there is a correlation
between physical and genetic distance, but that correlation is not perfect
(more on this point later). Thus, when using genetic maps to identify the
location of a gene we are taking advantage of the normal cellular
process of recombination
There are two types of maps used in locating genes: name them and explain how they are similar and different
genetic and physical maps.
Both maps contain useful, but different, information and thus complement one another.
A physical map measures distance between two loci in the genome in base pairs (e.g., determined by DNA sequencing), while a genetic map measures distances in the frequency of recombination events
complete linkage
no recombination occurs between the two genes
complete independence
independent assortment
testcross
is a cross between a heterozygous and a homozygous recessive individual, the latter is also referred to as the tester. Testcrosses are useful as you can determine offspring genotype simply by observing phenotype (as the offspring inherit only recessive alleles from the tester parent).
partial linkage
the proportion of recombinant progeny will fall somewhere in between 0 and 0.5 (or 0 to 50%). The proportion of recombinant progeny
can then be used to determine the genetic distance between the loci of
interest
phase
refers to the particular arrangement of alleles on a chromosome
recombinant frequency
The frequency with which a single chromosomal crossing occurs between two genes during meiosis
number of recombinant progeny/total progeny * 100
results of a test cross with complete linkage, independent assortment, linkage with crossing over