Pedigree Problem Solving Worksheet

Pedigree problem solving worksheet 1. Answer the questions below about this family’s pedigree. a. Is the pedigree shown below for an autosomal dominant or autosomal recessive trait? Give at 2 specific reasons for your answer. Autosomal dominant because: i. It doesn’t skip generation since a parent is affected. ii. The offspring are affected in equal frequency. Answer questions b-d using one of the following answers:  homozygous dominant  heterozygous  either homozygous dominant or heterozygous  homozygous recessive  either homozygous recessive or heterozygous b. What is the genotype of II-5? either homozygous dominant or heterozygous c. What is the genotype of II-6?  homozygous recessive d. If III-1 gets married to a normal man, what is the percentage chance that their child will have this trait? 50% 2. Answer the questions below about this family’s pedigree for a trait called Hitchhiker’s Thumb. a. Is Hitchhiker’s Thumb a dominant or recessive trait? recessive b. List one or two things that you observed that made you choose the answer to a. Either parent’s probably had a recessive allele of the gene Parents are related c. How are individuals E and F related? They are cousins and they share grandparents d. State which parent of E is likely to be the carrier (Hh) and explain why is that parent likely to be the carrier? Parent A is likely to be the carrier because the trait is an X-linked recessive trait which tends to skip over a generations if the affected sons have unaffected mothers e. (Bonus question) What is the chance that individual J is a carrier (is heterozygous)? 25% 3. Colorblindness is an X-linked recessive trait. A woman who is a carrier for colorblindness marries a man who has normal vision. Make a Punnett square for this couple and their predicted offspring below, using the following s y mb o l s : X=Xc h r o mos o mewi t hn o r ma lg e n e Xh=Xc h r o mo s o mewi t hc ol o r b l i ndg e n e Y=Yc h r o mo s o me X Xh X XX XhX Y XY XhY 4 a. What is the genotype of the woman? XhX b. What is the genotype of the man? XY c. What percentage of their children will be predicted to be colorblind? 50% d. What percentage of their sons will be predicted to be colorblind? 25% (continued on next page) 4. Below are family pedigrees for an inherited form of blindness called Leber congenital amaurosis (LCA). a. Based only on the pedigree in Figure 1, can you determine whether LCA is or isn’t inherited according to an autosomal dominant, autosomal recessive, or X-linked recessive pattern? For any possibilities that you ruled out, explain why. It is inherited because both parents have the gene making them homozygous dominant to the gene therefore, their kids will inherit said gene. b. Based only on the pedigrees in Figure 2, can you determine whether LCA is or isn’t inherited according to an autosomal dominant, autosomal recessive, or X-linked recessive pattern? For any possibilities that you ruled out, explain why. It might be autosomal recessive if both parents are heterozygous to the trait then ¼ their offspring is likely to be affected (continued on next page) Figure 3 shows the pedigrees of seven families with at least one member with LCA. These were used in 1998 to determine the inheritance pattern for the gene for LCA. c. Based on the pedigrees in Figure 3, is LCA inherited according to an autosomal dominant, autosomal recessive, or X-linked recessive pattern?  Use evidence from the pedigrees to support your claim, making sure to explain the evidence that rules out the inheritance patterns you didn’t choose. It might be autosomal recessive if both parents are heterozygous to the trait then ¼ their offspring is likely to be affected Use what you know about LCA’s inheritance pattern to write the genotypes for Family #4 in Figure 3, using L to represent an unmutated allele and l to represent a mutant, disease-causing allele for the LCA-related gene. d. What are the possible genotypes of both parents in this family? Explain your answer. L1- mother L1- father Both parents are heterozygous to the genes, so the offspring are recessive to the gene e. What are the possible genotypes of the female child without LCA? Explain your answer. LL 5. Shown below is a pedigree for a family with Hemophilia A, an X-linked disorder. a. Who did II-3 get the gene from: his mother or his father? father b. The genotype of II-3 is Xh Y. What are the genotypes of his mother and father? Mother: XX Father is Xh Y c. List all of the individuals in who are definitely carriers for Hemophilia A. II-3, III-5 and IV-1 d. If IV-1 and a woman heterozygous for the hemophilia A gene have a girl, what is the chance that she will have Hemophilia A? 50% e. If IV-1 and a woman with two normal alleles for hemophilia have a boy what is the chance that he will have Hemophilia A? 25%