(answered) – 1) In Hirschsprung Disease (also known as megacolon), there is anDescriptionSolution downloadThe QuestionAdvanced Genetics and Developmental Biology HW assignment. Has to be completed by Monday at 1pm1) In Hirschsprung Disease (also known as megacolon), there is an absence ofganglion cells, or aganglionosis, in the distal colon, which results in a functionalobstruction. Since these ganglia are missing, there is a loss of smooth musclecontraction/relaxation.A number of different chromosomal abnormalities and single gene defects havebeen associated with this condition. (6 points)a) In one family, cosegregation of the NF1 (neurofibromatosis 1) andmegacolon phenotypes was associated with inheritance of both an abnormalNF1 allele from one parent and an abnormal GDNF allele from the otherparent. Is this surprising? Why or why not?b) GDNF (glial cell line-derived neurotrophic factor) is a small, secreted homodimer. Following a concentrationgradient of GDNF, NCCs migrate between the midgut and hindgut. Without GDNF, NCCs are unable to leavethe midgut. NCCs migrate in the presence of GDNF, but addition of SHH reduces this migration by affectingthe responsiveness of NCCs towards GDNF signaling. Are GDNF molecules attractive or repulsive forNCCs? Describe one way you might test your theory in vitro.2) In Drosophila, gurken signals torpedo, which sets up a difference between the dorsal and ventral follicle cells thatproduce the eggshell, which is smooth on the ventral side, but has projections on the dorsal side. The Gd to Dorsalcascade (below right) is specific for controlling the D/V axis of the embryo only. (9 points)1You create a series of crosses so that you can study the eggs of female flies that are homozygous for null mutations ( -/-)of a number of different genes. These are the results:___1) Based on this information, what are the expected eggshell and embryo phenotypes of females homozygous for anull mutation of easter?A. embryo: dorsalized; eggshell: normalB. embryo: ventralized; eggshell: normalC. embryo: dorsalized: eggshell: dorsalizedC. embryo: ventralized: eggshell: ventralized___2) What are the expected eggshell and embryo phenotypes of females homozygous for a dominant allele of Toll thatproduces a Toll protein that acts as though it is always bound to a Sp?tzle protein?A. embryo: dorsalized; eggshell: normalB. embryo: ventralized; eggshell: normalC. embryo: dorsalized: eggshell: dorsalizedC. embryo: ventralized: eggshell: ventralized3) Briefly explain your answer for question 2.4) Trisomy 21 results in phenotypes collectively referred to as Down syndrome (DS) including heart defects, impairedcognition, gastrointestinal tract abnormalities and characteristic craniofacial structural abnormalities. Because NC is acommon precursor of many structures affected in DS, it has been hypothesized that trisomy 21 affects NC, although,until recently, no direct experimental evidence has been presented to support or refuted this hypothesis. A triploid2mouse strain (Ts65Dn) has been used as a model for Down syndrome in many studies (seehttp://dsresearch.stanford.edu/community/archive_issue_02.html).A recent study of Theiler stage 15 (T15) embryos showed that the volume of the first pharyngeal arch in Ts65Dn trisomicembryos was significantly reduced to 81% of euploid (p = 0.03) and there were significantly fewer neural crest cellscompared to euploid (20,711 vs. 25,125, p = 0.03). The second pharyngeal arch was also reduced in size and containedfewer NC in Ts65Dn at this stage. However, they found no differences at stage 14.Speculating that the neural crest deficit could be due to an aberrant response to Shh, the following experiment wasperformed. Cells from the first pharyngeal arch of trisomic or euploid T14 embryos were c
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