Question

In a routine prenatal screen, a clinical researcher finds that the karyotype of cells derived from a fetus shows potential trisomy (one of the chromosomes is present in 3 copies). It is not clear whether the extra chromosome is chromosome 6 or 7 (because chromosome 6 and 7 are quite similar in a simple chromosome spread analysis). To determine whether the extra chromosome is chromosome 6 or 7, the researcher performs polymerase chain reaction followed by RFLP analysis using DNA isolated from the father, mother and the fetus. Two target genes were amplified: VEGF (Vascular endothelial growth factor) located on chromosome 6, and TAS2R38 (PTC receptor protein) located on chromosome 7. The father and mother are homozygous for their respective alleles. In case of VEGF, the allele from the mother gets cut once by the enzyme BamHI, while the allele from the father does not get cut by this enzyme. In case of TAS2R38, the allele from the father gets cut by the enzyme SacI while the allele from the mother does not get cut by this enzyme. The VEGF PCR product was treated with BamHI, and the TAS2R38 PCR product was treated with SacI; all the reactions were analyzed through gel electrophoresis. Four possible results are shown below. In each scenario, choose the best options that match the data observed from the gel. (4 points)

NEW INFORMATION: Based on each of the gel data below, choose the option that explains i) Which chromosome shows trisomy? and ii) Where does non-disjunction occurs?

*Hint: The number of copies of the allele in an individual is reflected in the intensity (how thick/thin the bands) of the PCR product in the gel.

Which chromosome shows trisomy? Chromosome 6 Chromosome 7 Neither of the two. VEGF TAS2R38 a. b. C. a. b. C. Non-disjunction occurred during Egg formation Sperm formation Neither of the two. Which chromosome shows trisomy? Chromosome 6 Chromosome 7 Neither of the two. VEGF TAS2R38 d. e. f. v Non-disjunction occurred during d. e. f. Egg formation Sperm formation Neither of the two. Which chromosome shows trisomy? VEGF TAS2R38 g. Chromosome 6 h. Chromosome 7 i. Neither of the two. Non-disjunction occurred during g. Egg formation h. Sperm formation i. Neither of the two. VI vi. Which chromosome shows trisomy? VEGFTAS2R38 j. k. I. Chromosome 6 Chromosome 7 Neither of the two. iNon-disjunction occurred during j. k. I. Egg formation Sperm formation Neither of the two.

Answer 1

Which chromosome shows trisomy? Chromosome 6 Chromosome 7 Neither of the two. VEGF TAS2R38 a b. C. Non-disjunction occurred during a. Egg formation b. Sperm formation C. Neither of the two. Fetus intensity similar to mother. Mother is homozygous for chromosme 6 is same pattern is sehnl in fetus also In this band also mother chromosome 7 is similar to fetus chromosome 7. Which chromosome shows trisomy? VEGF TAS2R38 d. Chromosome 6 Chromosome 7 f. Neither of the two. v Non-disjunction occurred during -- -Ege formation e. Sperm formation f. Neither of the two.

Which chromosome shows trisomy? VEGF TAS2R38 g. Chromosome 6 Chromosome 7 i. Neither of the two. Non-disjunction occurred during g. Egg formation h Sperm formation i. Neither of the two. VI vi. Which chromosome shows trisomy? VEGFTAS2R38 j. Chromosome 6 k. Chromosome 7 Neither of the two. iNon-disjunction occurred during j. Egg formation k. Sperm formation Neither of the two.