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Transcript
MCDB 1041 Class 7 Visualizing inheritance patterns: Pedigrees Review session for Quiz 1 Friday 3:30 pm Porter B121—down the hall from coffee shop Learning goals: 1. Construct a pedigree from given information 2. Determine which mode of inheritance is most likely based on information in a pedigree 3. Calculate the likelihood of a genetic event based on a pedigree 4. Take into account information presented on a pedigree to exclude certain genotypes Dylan is genotype AaBB for two genes that cause recessive diseases. If his wife is aaBb, what is the chance his child will be a carrier for both diseases (AaBb)? a. 1 (100%) b. 3/4 4 possible different genotypes of offspring c. 1/2 and only one way to get AaBb, so ¼; d. 1/4 Or, think about it this way: ½ chance of getting Aa x ½ chance of e. 0 getting Bb, multiply togeter to get ¼ Carol is a carrier for two recessive disease alleles DdFf. Her husband is DDFF. What is the chance that their child will be a carrier of either the d or the f allele? a. 0 b. ¼ c. ½ 1/2 d. ¾ Because there are two possible different e. 1 Genotypes that lead to this pheontype: DdFF or DDFf (1/4 chance of each) Modes of inheritance Tells us about HOW traits are inherited Autosomal recessive Autosomal dominant X-linked recessive X-linked dominant Y-linked mitochondrial Most common An example of why pedigrees are used: Huntington s disease is a deadly genetic neurological and muscular disease that progresses over a course of 10-20 years (onset at 30-50 years of age) Alan s mother died before he was 5 years old, of Huntington s. His grandmother also died from the disease. Alan has a sister and a brother who are each already married. His sister has a son. Alan wonders if he is at risk. He finds out that there is a test to determine whether or not he will develop Huntington s later in life. Draw the pedigree of what you know about Alan’s family. What is his chance of developing Huntington’s? Autosomal dominant inheritance (examples: polydactyly, neurofibromatosis, Huntington Disease) Heterozygotes exhibit the phenotype. Autosomal recessive inheritance (examples: albinism, cystic fibrosis, sickle cell anemia, etc.) Heterozygotes have one copy of the recessive allele but exhibit the dominant (normal) phenotype Note: in many autosomal recessive pedigrees, carriers are not known (or shown) since they have a normal phenotype Practice! In the pedigree below, there could be carriers that are unmarked. What mode of inheritance is possible in the pedigree shown below? a) autosomal recessive b) autosomal dominant c) either I. II. 1 1 2 Dd, DD = normal dd = deaf 2 3 III 1 This pedigree shows a family with a form of deafness that is inherited in an autosomal recessive manner. Members of the family with filled symbols are deaf. Which members of this family are definitely heterozygous (Dd)? A. I-1 and I-2 B. I-1, I-2, and II-1 C. I-1, II-1, and II-3 D. I-1, I-2, and II-3 E. I-1, I-2, II-1, and II-3 Up until now, we ve really only thought about autosomal chromosomes. What about the X and Y chromosomes? Sex chromosomes The sex of an individual is determined genetically by the sex chromosomes. X and Y -> male X and X -> female • Men only have 1 X chromosome • Men pass on an X to daughter, Y to son X © Biophoto Associates/Photo Researchers Y X-linked recessive traits • Males inherit an X only from mom while females inherit an X from each parent • Because males inherit their only X from their mother, an X-linked pedigree often has carrier females with affected sons. Affected son X-linked recessive inheritance hemophilia X-linked dominant inheritance: As with an autosomal dominant trait, inheriting a single allele gives you the trait example: congenital generalized hypertrichosis (probably where werewolf legends came from) What is the most likely outcome if you can observe the children of the affected women in generation III (assume they all have children with normal, noncarrier males)? a. All male children (and only males) will have the trait b. All females (and only females) will have the trait c. Some males and no females will have the trait d. All males and females will have the trait e. Some males and some females will have the trait Matt and Sue have 14 children, 7 boys and 7 girls. All 7 girls have X-linked dominant hypophosphatemia and all 7 boys are normal. People with hypophosphatemia typically show symptoms when they eat a lot of carbohydrates, so one can have the disease and not know it. X- = the X with the mutation X+ = the normal X The genotype for Sue that is most consistent with this information is: A). X+X+ B). X+XC). X-X- Another practice question Mary is a carrier of an X-linked recessive disease and a carrier of an autosomal disease. If Mary has a child with a man who has only non-disease alleles, what is the chance their child will have the X-linked disease? a. 0 b. ¼ c. ½ d. ¾ e. 1