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Genetics Lab Cystic Fibrosis Information source: http://www.ornl.gov/sci/techresources/Human_Genome/posters/chromosome/cftr.shtml Cystic fibrosis is a serious genetic disorder caused by a deletion mutation, ΔF508, of the CFTR (cystic fibrosis transmembrane conductance regulator) gene located on chromosome 7. The normal CFTR protein product is found in membranes of cells that line passageways of the lungs, liver, pancreas, intestines, reproductive tract, and skin. The protein helps cells keep salt in balance. When the normal protein is synthesized by ribosomes, the Golgi apparatus transports it along the endoplasmic reticulum for packaging. If the protein is normal the Golgi apparatus sends it to the membrane where it can control active transport of chloride. When a CFTR protein with a ΔF508 mutation reaches the endoplasmic reticulum, the ER recognizes the protein as defective and marks it for recycling. As a result the protein never becomes part of the membrane. Individuals who are heterozygous for the ΔF508 mutation are called carriers. An individual who inherits two alleles with the ΔF508 mutation will have cystic fibrosis and he or she will build up a dangerous thick sticky mucus coating along the lungs and digestive organs. Barbie and Ken have been referred to the lab by their daughter Sally’s pediatrician for cystic fibrosis testing. No one in Barbie or Ken’s families has cystic fibrosis. Sally’s DNA sequence and m-RNA transcription are shown below. Translate the m-RNA into t-RNA. Use the amino acid chart to convert the t-RNA to amino acids. Compare Sally’s amino acid sequence to the normal amino acid sequence. Normal Amino Acid Sequence Ile Ile Phe Gly Val 506 507 508 509 510 Sally’s Gene Segment DNA ATC ATT GGT GTT ACT m-RNA UAG UAA CCA CAA UGA t-RNA Amino acid Does Sally have cystic fibrosis? Explain your diagnosis. Use the chart of find the amino acid coded by the transfer RNA. ΔF508 Pedigree Chart Roberts Family Bill Ann Midge Carson Family Skipper Dan Karen Barbie Ken Jill Brad Sally The Roberts and Carson families were tested for the ΔF508 mutation. The results are shown on the pedigree chart. Fill in Sally’s result based on your testing. Construct a Punnett Square for Ann and Bill and for Karen and Dan. Use C for the dominant normal allele and c for the recessive defective allele. Dan Karen Ann Bill What were the chances of Ann and Bill having a child with cystic fibrosis? What were the chances of Karen and Dan of having a child with cystic fibrosis? Why didn’t cystic fibrosis appear in earlier generations? Barbie and Ken have been referred to you for genetic counseling. What can you tell them based on Punnett Square analysis? Errors During Meiosis Meiosis is the cell division process that ends with four daughter cells with half of the normal chromosomes. In humans, the egg cells and sperm cells undergo meiosis to form four haploid (half number) gametes. Sometimes errors occur during the division process that result in cells with an additional chromosome or a deleted chromosome. Usually gametes with an unusual number of chromosomes simply do not have the opportunity to become an embryo. Although meiosis errors may occur in sperm cells, the greater number of meiosis errors occur in egg cells. Chromosome errors during meiosis are more common among women who conceive after age 40, but can occur at any age. Amniocentesis is a screening process that uses a sample of the amniotic fluid surrounding the developing fetus to determine a karyotype. Organizing the chromosomes into pairs creates a karyotype. The table below shows some common syndromes caused by known abnormalities. Syndromes Abnormality Occurrence per 10,000 births Lifespan (years) Down’s Trisomy 21 15 40 Edward’s Trisomy 18 3 <1 Patau’s Trisomy 13 2 <1 Turner’s Monosomy X 2 (female births) 30-40 Kleinfelter’s XXY 10 (male births) normal Source: http://genome.wellcome.ac.uk/doc_wtd020854.html You have received an amniocentesis sample from an obstetrician. Analyze the karyotype. Report the gender of the fetus and any abnormality. If there is an abnormality, identify the syndrome. Gender Abnormality Syndrome Duchenne Muscular Dystrophy Information source: http://yourgenesyourhealth.org/dmd/whatisit.htm Duchenne muscular dystrophy is the most common form of muscular dystrophy. It occurs more frequently in boys than in girls. The symptoms of muscle weakness begin between 3 and 5 years of age with a rapid progression of weakness. By age 12, most affected boys are unable to walk. Muscle weakness will progress to the respiratory muscles requiring the use of a ventilator in the final stages. Symptoms of Duchenne muscular dystrophy are caused by the absence of dystrophin, a protein involved in maintaining the integrity of muscle. The gene that codes for dystrophin is located on the X chromosome. Kevin and Karen Emmitt have come to you for genetic counseling. Karen had a brother who died from Duchenne muscular dystrophy. Kevin has no history in his family. Their chromosome analysis has been used to construct a Punnett square. XM normal allele Xm muscular dystrophy allele Duchene MD is a condition caused by an X-chromosome linked recessive allele. Karen Emmitt Analyze the Punnett Square of the Emmett Family and then answer the questions. NOTE: Probability is based on four possible outcomes. Express your answer as a percentage Kevin Emmett XM Y XM XM XM XM Y Xm XM Xm Xm Y If the couple has a daughter, what is the probability that the couple will have a daughter with MD? If the couple has a daughter, what is the probability that the couple will have a daughter who is a carrier of MD? If the couple has a son, what is the probability that the couple will have a son with MD? Is it possible for a son to be an MD carrier? Explain. Why are males more likely to have MD than females? Explain.