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Name ___________________ Date ____________________ Applied Genetics Punnett Squares A. The disease cystic fibrosis is caused by the recessive allele n. 1. What percentage of the children of a couple with genotypes NN and Nn will probably have cystic fibrosis? __________________ Parent genotypes: ________ X ________ F1 genotypic ratio: __________________ F1 phenotypic ratio: _________________ 2. If both parents are heterozygous for cystic fibrosis, what percentage of the children will probably have the disease? ________________ Parent genotypes: ________ X ________ F1 genotypic ratio: __________________ F1 phenotypic ratio: _________________ B. Phenylketonuria (PKU) is an autosomal recessive genetic disease in which the body cannot safely break down the amino acid phenylalanine. If a modified diet is not strictly observed, PKU will cause severe brain damage. To avoid this problem, people with PKU must eat a diet low in phenylalanine. A normal couple has a child with PKU. 1. What is the probability that this couple’s next child will have PKU? ___________________ 2. What is the probability that this couple’s next child will be homozygous for the normal allele? ____________ 3. What does Nutrasweet© contain? ______________________ 5. What does this have to do with PKU? ____________________ ________________________________________________ C. Achondroplasia, one form of dwarfism, is caused by the dominant allele A. Embryos with the genotype AA do not survive. Suppose a couple with achondroplasia get married and have children. 1. What phenotypic ratio would you observe in the couple’s children? _______________________ 2. One of this couple’s children, who has a normal phenotype, marries a person who is also a normal phenotype. What percentage of the children from this marriage is likely to have achondroplasia? _____________________ 3. In most cases of achondroplasia, two normal parents have a child with achondroplasia. How can this happen? ____________________________________________________________________ Human Pedigrees A. Use the following symbols to work out the next problem: Normal male XBY Normal female b Color-blind male X Y Color-blind female I 1 XBXB or XBXb XbXb 2 II 3 4 5 6 7 III 8 9 10 11 12 13 IV 14 1. 2. 3. 4. 5. 6. 15 16 17 18 19 What does a square mean in a pedigree? Male Female Undetermined What does a circle mean? Male Female Undetermined When should a square or circle be colored in? ___________________________________________ What is the genotype of a color-blind male? ______________ What is the genotype of a color-blind female? ____________ Write all genotypes for all individuals in the pedigree chart and indicate carriers by half-filled circles/squares. B. Huntington Disease, a disease of the nervous system, is caused by an autosomal dominant gene. The pedigree chart below illustrates a family with individuals who have Huntington disease. Homozygous dominant is lethal to the fetus. Use the chart to answer the questions that follow. I 1 2 II 3 4 5 6 7 8 9 III 10 11 12 13 14 15 What is the probable genotype of person 4 in generation II? ________ Explain. ____________________________________________________________________ What are the probable genotypes of individuals 8 and 9 in generation II? ________________ Explain. ____________________________________________________________________ What is the probability that person 14 in generation III will NOT have Huntington disease? __________________________________________________________________________ 6. Use the color yellow to shade in the shapes of those individuals who can be determined to carry the Huntington gene. 7. Identify the individuals whose genotypes cannot be determined without more information by putting a question mark in their square or circle and coloring the shape blue. 1. 2. 3. 4. 5. C. Duchenne Muscular Dystrophy is a deadly disorder in which the muscles grow progressively weaker. The disease is caused by a recessive gene on the X chromosome. The pedigree chart below illustrates the inheritance pattern of this gene. Use the chart to answer the questions that follow. Normal male XDY Normal female XDXD or XDXd d Duchenne male X Y Duchenne female XdXd I 1 2 II 3 4 5 6 III 1. 2. 3. 4. 5. 7 8 9 10 11 Is Duchenne Muscular Dystrophy more likely to occur in males or females? Males Females Explain. __________________________________________________________________ Individual 8 in generation III is a female with this disorder. How did she inherit this disease? __________________________________________________________________ Individual 11 in generation III has this disorder, yet his father did not. How is this genetically possible? __________________________________________________________________ Individual 7 from generation III does not have the disease, yet his mother was a carrier and his father had the disease. How is this possible? __________________________________ __________________________________________________________________________ D. Autosomal Recessive Polycystic Kidney Disease (ARPKD) is a genetic disorder in which multiple fluid-filled cysts develop on the kidneys resulting in enlarged and damaged kidneys. In the blanks provided, write as much of the genotype as can be determined from the information provided. Assume the shaded symbols represent the homozygous recessive genotype, pp. Be sure to correctly identify carriers. The trait is NOT sex-linked. I II III