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NAME _______________________________________ PER _________ PEDIGREE ANALYSIS Many traits in humans are controlled by genes. Some of these traits are common features like eye color, straight or curly hair, baldness, attached vs. free ear lobes, the ability to taste certain substances, and even whether you have dry or sticky earwax! Other genes may actually cause disease. Sickle cell anemia, muscular dystrophy, cystic fibrosis are each caused by a specific allele of a human gene, and can therefore be inherited from one generation to the next. Inheritance of Albinism To learn more about how genetic traits are inherited, we will consider a specific example -- the gene that controls whether or not a person can produce the pigment melanin which contributes to the color of skin, eyes and hair. Some people have the hereditary condition, albinism; they are not able to produce melanin and have little or no pigment in their skin and hair. Two different versions of the same gene are called alleles. One allele of this gene codes for melanin production and normally pigmented skin and hair; it is symbolized by A. Another allele of this gene codes for albinism; it is symbolized by a. Human geneticists illustrate the inheritance of a gene within a family by using a pedigree chart. On such a chart, males are symbolized by a square (□) and females are symbolized by a circle (○). People who are affected by a disease are symbolized by a dark circle or square. Normal Male = □ Genotype AA or Aa Normal Female = ○ Genotype AA or Aa Albino Male = Albino Female = Genotype aa Genotype aa 1 The pedigree chart below shows inheritance of the gene that causes albinism. A and B represent a couple who had five children, including C and E. Only one of the children, E, was albino. E and her husband had five children, including G. In the pedigree below write the genotypes of the individuals who are labeled with letters, using (A) to represent the dominant allele and (a) to represent the recessive allele. Start by indicating the genotypes of E and F. Then use a Punnett Square to figure out what the genotypes for C and D must be. Next, determine the genotypes of A and B. Finally, determine the genotype of G. A C B D E G F Genotype of E: ________________ F: ________________ Based on what you wrote for F above, what must the genotypes of both C and D be? ______ Show your reasoning by filling out the square (crossing C and D) below: Based on what you determined for C above, and what you know about E, what must the genotypes for A and B be? _____________. Show your reasoning by filling out the square (crossing A and B) below: 2 What do you think G’s genotype is? ___________. Show your reasoning by filling out the square (crossing E and her husband) below: Challenge Question Shown below is a pedigree chart for the inheritance of achondroplasia (ay-kon-druh-playzhuh), a form of dwarfism. Dark circles or squares indicate individuals with achondroplasia. Examine the pedigree chart, and answer the following questions. Is the gene that causes this form of dwarfism a recessive or dominant trait? How do you know? Using (D) to represent the dominant allele and (d) to represent the recessive allele, write the genotypes of the indicated individuals on the pedigree below. For one of the labeled individuals, there are two possible genotypes. Write both genotypes and indicate which one is more likely. A C B D E F G Based on the frequency of dwarfs among the people you have seen in your lifetime, do you think that the allele for achondroplasia is common or rare in the population? 3