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MAPPING HUMAN CHROMOSOMES (Mapping with DNA markers ((mircosatellites…
MAPPING HUMAN CHROMOSOMES
X chromosome mapping
1st human chromosome mapped :scream_cat: bc it is easy to controlled and detect the results of recombination :scream: bc males are hemizygous (only one copy of X chromosome) :arrow_forward: gives a close approximation to a
testcross
when mating a male
w
a dihybrid female
able to define the location of each gene in X-chromosome
Somatic-cell hybridization
mature somatic cell can undergo a limited number of cell division :warning:
BUT
can alter by viruses
Cells from 2 different species can be
fused
:arrow_right: cell has two different nuclei :arrow_right:
heterokaryon
two nuclei fuse together eventually (
unknown reason
) :arrow_right_hook: chromosome of one species are lost
preferentially
only occurs in tissue culture
:check: Human-Mouse somatic cell hybrids
culture the human fibroblasts and mouse tumour cells
in presence of antifree drug
:arrow_forward: heterokaryon formation :arrow_forward: the fusion of human and mouse nuclei :arrow_forward: different human chromosome are lost in different cell lines
(bc mouse chromosomes are dominated)
analysis
: each line containing a different subset of human chromosomes :!!: able to give a clue of the location of particular genes :star: eg:
which chromosome contains a specific gene
able to give more precise location (
on which part of chromosome
) by using irradiated hybrid cells where portion of chromosome (containing the specific gene) is deleted
In situ hybridization
Determining the
chromosomal location
of genes through
molecular analysis
Requires a
probe
for the gene :pen: a single stranded and complimentary to the gene
fluorescently labelled :arrow_right: visible under UV light :arrow_right: site of hybridization is easily detected
able to use multiple probes w different dye
:spiral_note_pad:The probe and target (been already denatured entirely)
hybridize
on microscope slide
useful in diagnosis
Down's Syndrome with chromosome 21 :warning: for
Amniocentesis
(amniotic fluid test)
can detect the mutation because of loss or gain of chromosome
CML by translocation btwn chromosome 9 and 22 =>
philadelphia chromosome
Mapping with DNA markers
The markers are variable genes with easily observable phenotypes :arrow_right: cooperate with banding pattern ( genetic tree family model) :arrow_right: can detect the disease gene
(around the DNA marker)
can be mapped by recombinant frequency
mircosatellites
simply sequence with
2-6bp
:explode: most common is CA (its compliment is GT) :warning: based on variation
minisatellites
tandem repests with
15-100bp
single nucleotide polymorphisms
single base pair difference in DNA sequence btwn individuals of a species
Restriction fragment length polymorphism
is SNP
alters a restriction enzyme recognition site
:check: Linkage analysis
using a model of testcross with specific alleles marked by DNA markers
able to estimate the distance between the specific alleles by DNA markers
:star: been used for detecting the genes responsible for Huntington disease
:check: Genomewide association studies
compare the DNA of participants having varying phenotypes for a particular trait or disease
linkage disequilibrium
non-random association between alleles in a haplotype :warning: the closer the mutation is to the alleles (strong association):arrow_right: the longer LD persists the
crossover
:arrow_right: provide the distance btwn genes