Down
syndrome is the result of one more or less copies of human chromosomes 21 where
the occurrence is 1 of every 700-800 live births. Individuals experiencing Down
syndrome display wide range of phenotypic characteristics (severities) which
include facial dysmorphology, cognitive impairment, behavioral anomalies and
congenital heart defects. Although these traits are specifically identified as
typical for individuals with Down syndrome, however precise genetic and
molecular mechanisms that causes these specific traits are not well understood.
It has been thought that the trisomy of ‘Down Syndrome critical/chromosomal region’ is responsible
for most of the phenotypic traits of Down Syndrome however more researches have
been conducted in mice in which prove that the ‘Down Syndrome
critical/chromosomal region’ is in fact not sufficient to cause craniofacial
features, a common characteristic of Down Syndrome.
This
experiment aims to prove how ‘Down Syndrome Critical/chromosomal region’ is not
the only factor that causes the characteristics in individuals but genes of
each individuals. Experimental mice from different genetic background, both
experiencing Down Syndrome conditions were compared regarding the size of their
mandible and craniofacial phenotypes. The first group of mice was a 'standard' Down syndrome mice since these specific groups are typically used in many if not all of experiments and trials concerning down syndrome. The second group of mice came from a mixed background. Mice that developed from mixed genetic background have a larger
overall size of morphologically different mandible than the other mice. In
addition, there were also in cerebellar and brain size and behavioural tests of
learning and memory.These discoveries that have been found during myriad of
mice with down syndrome shows that the differences may be due to genetic
background difference. This experiment presents evidence that allelic
differences in trisomic and nontrisomic genes as well as trisomc gene content
all contribute to phenotypic differences shown in mandibular precursor
development.
All of the
mice used within this experiment were bred for many generations to stabilize a
certain trait and to exclude other possible traits that may affect development
of that desired trait. The investigation as well focuses on the embryonic
samples which had been implanted with Down Symdrome to explore size
differences. From the embryo, RNA were extracted from the cells and through the
techniques of PCR (polymerase chain reaction), amplification of DNA were
rendered then examined. These two factors being investigated (embryonic samples
and DNA) support the hypothesis of which allelic differeces in trisomic content
and genetic background cause viariety in Down Syndrome phenotype such as
differences in body size (pre and post natal), mandibular precursor.
Within the
experiment, mice from different genetic background were compared. Identical
methodologies were used as well as same environmental conditions. These two
factors would assure that no other factors would affect the development of each
type of mice. The differences being presented within these mice were the size
of mandibular precursors, size and volume of embryos, size of the brain and as
well as each individual’s ability to learn. The hypothesis made in the beginning of this experiment has been proven to be correct.
It's mind boggling to think of all of the advancements of medicine that are related to mice research. This is just one example of how scientists have designed lab experiments that have given us insights into small and large phenomena. The fact that there are mice strains for even Down's Syndrome is amazing.
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