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Pedigree Analysis • Recognizing different patterns of inheritance within different types of pedigrees • Textbook p. 611-617 Tee hee What is a Pedigree? • Diagram or flowchart that uses symbols to show patterns of relationships & traits in a family over many generations • 4 patterns of inheritance to be analyzed: 1. Autosomal recessive 2. Autosomal dominant 3. Sex-linked recessive 4. Sex-linked dominant http://media.syracuse.com/news/photo/2010/06/ugliest-dog-dies-ny114jpg-f63d008d5e193838.jpg Symbols in Pedigree Charts Symbols in Pedigree Charts p. 612 Examples http://commons.wikimedia.org/wiki/File:Pedigree-chart-example.png Dominant sex-linked Recessive autosomal Dominant autosomal Recessive sex-linked Allele Notation • Dominant autosomal trait: the affected allele = “A” and the unaffected allele =“a” • Recessive autosomal trait: the affected allele = “a” and the unaffected allele = “A” • Dominant sex-linked trait: the affected allele = “XA” and the unaffected allele = “Xa” • Recessive sex-linked trait: the affected allele = “Xa” and the unaffected allele = “XA” Pedigree Analysis Step 1: Determine whether the trait demonstrated by the pedigree is dominant or recessive Step 2: Determine whether the trait is sexlinked or autosomal. To do this, you must look for evidence of certain patterns of inheritance. The Pedigree Decision Tree Step 1: Dominant or recessive? • Use the decision tree and look for evidence! Why do heterozygotes indicate a recessive trait? Heterozygote = carries the gene but does not display the trait If recessive trait, an individual with Aa will appear as this OR If dominant trait, an individual with Aa will appear as this: Dominant or recessive? Recessive! Unaffected parents produce affected offspring Dominant or recessive? Dominant! All affected individuals have an affected parent Dominant or recessive? Recessive! Heterozygotes AND unaffected parents produce affected offspring Remember the steps: Step 1: Determine whether the trait demonstrated by the pedigree is dominant or recessive • Once you do this, you are ready to go to step 2! Step 2: Determine whether the trait is sexlinked or autosomal. - The evidence you look for depends on your answer for step 1 The Pedigree Decision Tree For recessive pedigrees Step 2: Autosomal or sex-linked? • Use the decision tree and look for evidence! For recessive pedigrees Step 2: Autosomal or sex-linked? RECESSIVE AUTOSOMAL if: • Male carriers/heterozygotes • Affected female has unaffected parents RECESSIVE SEX-LINKED if: • If carrier mother x unaffected father has affected son • No affected females, suspect sex-linked Example 1) Recessive or Dominant? 2) Autosomal or Sex-Linked? Recessive! Unaffected parents produce affected offspring Autosomal! Unaffected parents produce affected daughter Example 1) Recessive or Dominant? 2) Autosomal or Sex-Linked? Carrier mother x unaffected father producing affected sons Recessive! Heterozygotes AND unaffected parents produce affected offspring For dominant pedigrees Step 2: Autosomal or sex-linked? • Use the decision tree and look for evidence! For dominant pedigrees Step 2: Autosomal or sex-linked? IF DOMINANT, the pedigree must be DOMINANT AUTOSOMAL if: • Affected father has unaffected daughter • Affected father has affected son with unaffected mother DOMINANT SEX-LINKED if: • Affected father has all affected daughters and no affected sons Dominant Autosomal Pedigrees • Affected father has unaffected daughter Because father MUST be a carrier genotype = Aa Unaffected daughter MUST be aa • Affected father has affected son with unaffected mother Since the father gives the allele to the son, it must be autosomal Dominant Sex-Linked Pedigrees • Affected father has all affected daughters and no affected sons XA Y Xa X AX a X aY Xa XA Xa Xa Y All affected daughters No affected sons Example 1) Recessive or Dominant? 2) Autosomal or Sex-Linked? Autosomal! Affected father produces unaffected daughters Dominant! All affected individuals have an affected parent Example http://commons.wikimedia.org/wiki/File:Pedigree-chart-example.png 1) Recessive or Dominant? 2) Autosomal or Sex-Linked? Dominant! All affected individuals have an affected parent Sex-linked! Affected fathers produce all affected daughters AND no affected sons http://commons.wikimedia.org/wiki/File:Pedigree-chart-example.png The Pedigree Decision Tree Genotyping Dominant Genotype autosomal aa Recessive Genotype autosomal AA or Aa Dominant Genotype sex-linked Xa Xa Recessive Genotype sex-linked XAXA or XAXa Genotyping Dominant Genotype autosomal Recessive Genotype autosomal Dominant Genotype sex-linked Recessive Genotype sex-linked aa AA or Aa Xa Xa XAXA or XAXa aa AA or Aa aa Xa Y XAY XAXA or XAXa XAY Xa Xa AA or Aa AA or Aa aa Aa Aa Xa Y XAXa Pedigree Practice a. Recessive or dominant trait? How can you tell? b. Autosomal or sex-linked trait? How can you tell? c. Identify the genotypes. Pedigree Practice a. Recessive or dominant trait? How can you tell? b. Autosomal or sex-linked trait? How can you tell? c. Identify the genotypes. Pedigree Practice Pedigree Practice Pedigree Practice Q: did you notice that the last pedigree was the same example from earlier in this lecture?!? Pedigree Practice Chapter 17 What you need to know about pedigrees: • How to be able to recognize the patterns of inheritance associated with the four types of pedigrees: dominant autosomal, dominant sex-linked, recessive autosomal, recessive sex-linked