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SCIENCE & TECHNOLOGY

The unique sequences generated regulating specific biological linkage study for estimation of LOD
from the clones determined the ESTs mechanisms. score to determine marker-gene/QTL
for tissue specific expression. About Further, intensity of expression of relationship in F 2 progeny. This
6739 ESTs from abdominal fat tissue, ESTs worked out from DNA mapping study is very much effective
5541 ESTs from liver tissue, 5764 microarrays reveal the fold change of for exploring genetic marker for
ESTs from breast and leg muscle, 8737 expression between two divergent specific trait to be ultimately used for
ESTs from pituitary gland/ lines. The DNA microarrays were genetic improvement program in
hypothalamus/pineal gland and 3828 analysed in hypothyroid versus chicken. Most of the mapping studies
ESTs from oviduct/ovary/testis have hyperthyroid chickens for exploring the to date are using 150 - 300 markers
been established. A large chicken EST role of specific ESTs or the genes in for genomic scans to estimate level of
database developed from high regulating thyroid activities in chicken. linkage disequilibrium. The genetic
through-put sequencing of 2,99,506 They induced chicken by feeding marker is defined as a genetic variant
clones prepared from 21 normalised propylthiouracil for hypothyroid which is associated with the traits and
tissue-specific cDNA libraries of layer- chicken and by triiodothryronine (T 3 ) easy to observe showing simple
type chicken revealed 3,39,314 EST for hyperthyroid chicken. They genetic inheritance. The first markers
sequences in BBSRC collection. collected liver from both hypo as well identified for breed characterization
These EST data bases are extensively as hyperthyroid chicken and DNA were phenotypic traits like feather/
used for preparation of DNA microarrays were developed. The plumage/coat colour variants.
microarrays. comparative analysis reveals the Successively, protein/enzyme/blood
The preparation of high through- expression of different genes at group polymorphisms were found but
put expression profiling needs DNA different rates in both the groups. the number of markers was too low to
chip technology or DNA microarrays. The identification of functional create a genetic map with good
Keeping the importance of immunity gene is not only important for genome coverage.
and prophylaxis in mind, chicken physiological study but also be used To obtain higher genetic variability,
lymphoid DNA arrays have been for genetic marker study. For marker nucleotide based variation was then
prepared from the already available analysis, crossing of two divergent considered and consequently,
knowledge of lymphoid ESTs to lines with back crossing is utmost restriction fragment length
examine gene expression profiles in important to analyze inheritance of the polymorphisms or RFLPs based on
normal and challenged lymphoid functional gene along with QTL sequence differences at restriction
tissues. The chicken metabolism/ (Quantitative trait loci) regulating the enzyme target sites was considered as
somatic system microarrays, an 11K trait. If QTL is found to be linked with first DNA marker. Later on mini
DNA chip is available where a non- the gene, they will be inherited together satellites and microsatellites were
redundant set of 11,000 ESTs as a block. Finally, with linkage discovered as length polymorphisms
prepared from liver, abdominal fat and disequilibrium analysis, gene-QTL in tandem repeated sequences. The
skeletal muscle is available for the marker relationship can be explored. repeated unit in a mini satellite varies
study of expression profiling. The A QTL scan of the F 2 progeny from a from 10 to 60 bp while in a
chicken neuroendocrine/reproductive cross between genetically lean and fat microsatellite, it varies from 1 to 9 bp.
system microarray, an 8K DNA chip mice revealed an obesity-related QTL The main advantages of
developed from ESTs of pituitary/ near a cluster of thyroid genes on microsatellites are that they are highly
hypothalamus/pineal gland and chromosome 15. abundant and evenly distributed
reproductive tract (oviduct/ovary/ The spot14 of DNA microarray was throughout the genome as compared
testis) is available at Delaware revealed as polymorphic and up- to mini satellites that can be too large
Biotechnology Centre. regulated when T 3 is fed to the to be detected by PCR and show a
The DNA chips are very much chicken. The expression of spot14 is non-random distribution.
useful to develop global gene dramatically increased in the liver of Microsatellites are highly polymorphic
expression profiling with minimal chicks after hatching and it is involved and can easily be detected with PCR
redundancy. Currently, system-wide in deposition of abdominal fat while facilitating high-throughput
DNA microarrays are available for age progressed. Ultimately, spot 14 genotyping in large pedigrees and are
gene expression study in longitudinal was called as a thyroid hormone- the most commonly used marker for
manner (at different time points). In inducible gene. By linkage mapping, linkage studies. The most advanced
near future, global gene expression these genes or QTLs can be mapped markers are the single nucleotide
profiling in multiple tissues will aid to efficiently. polymorphisms (SNP) which directly
develop a detailed genetic blueprint Chromosome specific control the trait either in quantitative
illustrating the developmental events microsatellite or other markers are or qualitative way.
and concomitant hierarchy of genes available with us and be used for (PTI Feature)

76 Competition Wizard March 2018