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Pedigree Analysis Key Words or Phrases • • • • • • • • • Pedigree Inheritance Autosomal Dominant Recessive Sex linked Gene therapy Biochemical testing Viral vectors Goals of Pedigree Analysis • 1. Determine the mode of inheritance: dominant, recessive, partial dominance, sex-linked, autosomal. • 2. Determine the probability of an affected offspring for a given cross. Basic Symbols More Symbols Mating Offspring Example of a Pedigree Chart • A pedigree chart shows the incidence of a certain condition as it goes through several generations Types of Inherited Traits • As you know, some traits are dominant and some are recessive. • If you look closely at a pedigree chart you may be able to find clues about what kind of inheritance it is • For example, this chart shows the incidence a recessive trait Q: How do we know? A: The first generation (I) do not have affected parents yet one of their offspring has the trait Recessive Autosomal Pedigree Autosomal Dominant • Only one copy of the gene will give someone the condition • All unaffected individuals are homozygous for the normal recessive allele. • If one parent has the condition, a child has a 50% chance of inheriting it Dominant Autosomal Pedigree I 2 1 II 1 2 3 4 5 6 III 1 2 3 4 5 6 7 8 9 10 Dominant vs. Recessive • Is it a dominant pedigree or a recessive pedigree? • 1. If two affected people have an unaffected child, it must be a dominant pedigree: D is the dominant mutant allele and d is the recessive wild type allele. Both parents are Dd and the normal child is dd. • 2. If two unaffected people have an affected child, it is a recessive pedigree: R is the dominant wild type allele and r is the recessive mutant allele. Both parents are Rr and the affected child is rr. • 3. If every affected person has an affected parent it is a dominant pedigree. Sex-Linked Traits • Most genes are on the • Example of a Y autosomal chromosomes linked condition (the first 22) • But some may be on the sex chromosomes • If the affected gene is on the Y chromosome, then only men can get it • All direct male descendants will inherit the condition Sex – Linked Traits • A sex linked trait may also be on the X sex chromosome • If the trait is recessive, men are still most likely to inherit the condition because women have two copies of the gene and men only have one • So women are more likely to get at least one copy of the normal, dominant gene • Example of X linked recessive trait • Not all men will inherit the condition but men are more likely to inherit the condition than women Sex-Linked Dominant • Mothers pass their X’s to both sons and daughters • Fathers pass their X to daughters only. • Xd = recessive normal allele • XD = dominant mutant allele • If only the male has the trait then all daughters would have the condition but not the sons. Genetic Testing • Individuals at risk of inheriting Method a genetic disorder may get tested in different ways Karyotype What is Analyzed Example Chromosome number and sizes Down Syndrome Fluorescent Hybridization Fluorescent image of chromosome can allow irregularities to be seen Chronic Myelogenous leukemia is a translocation disorder Gene Testing Sequence of DNA bases on a gene can show mutations Cystic Fibrosis Biochemical Testing Testing for proteins that are indicative of a disease Tay Sachs disease Gene Therapy • Gene therapy is a way of curing a genetic disease by inserting a normal gene into the cells that are affected • If scientists can obtain a normal copy of a mutated gene they can put it inside a virus and inject the virus into an affected person • Viruses can insert their DNA into the cells and allow the cells to make a normal protein instead of a mutated one • Still very new, gene therapy has been used to treat certain types of heart disease and immune disorders