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Pedigrees

Pedigrees. Analyzing family relationships for genetic clues. Pedigree diagram. A pedigree is a diagram of the individuals and their relationships in a family group. People are represented by symbols. Lines show the connections between people. Purpose:

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Pedigrees

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  1. Pedigrees Analyzing family relationships for genetic clues

  2. Pedigree diagram • A pedigree is a diagram of the individuals and their relationships in a family group. • People are represented by symbols. • Lines show the connections between people. • Purpose: • To determine the mode inheritance of a genetic disease. • To estimate the risk of passing on a genetic disease.

  3. Symbols • Males are square. • Females are round. • Affected individuals are dark. • Normal or unknown are white. • Horizontal lines are matings. Parents • Vertical lines are between generations

  4. Who is who? • The oldest generation is at the top of the diagram. • Newest generation is at the bottom. • Generations are counted from the oldest generation using Roman numerals. • Count top to bottom • Individuals can be numbered. • Left to right

  5. Three Types of Inheritance • Each type has a distinctive pattern • Autosomal Dominant • Autosomal Recessive • Sex-Linked Recessive

  6. Autosomal Dominant • Present in each generation. No skipping. • Males and Females are equally likely to be affected. • Each affected person has an affected parent. • Unaffected person has unaffected offspring. WHY?

  7. Autosomal Recessive • Must be homozygous to be expressed. • If child is rr, then the parents must be _____. • Recessive can skip generations.

  8. Sex-Linked Recessive • Recessive may skip generations. • Males have one X, and males are more likely to be affected. • Never passes from father to son. • An affected male gets his X from his mom, II-2. • What is her genotype? X Xc or XcXc

  9. Test the pedigree for a pattern • Mark the genotypes. • Try the three patterns. • What pattern is possible? Use these letters for Sex Linked only. XA = normalXa = the trait (a genetic disease or abnormality)Y = Y chromosome (males only) Autosomal Dominant Autosomal Recessive Sex-Linked Recessive

  10. What is the pattern? • Mark the genotypes. • Try the three patterns. • What patterns are possible? Use these letters for Sex Linked only. XA= normalXa = the trait (a genetic disease or abnormality)Y = Y chromosome (males only) Autosomal Dominant Autosomal Recessive Sex-Linked Recessive

  11. What is the pattern? • Mark the genotypes. • Try the three patterns. • What pattern is possible? Use these letters for Sex Linked only. XA = normalXa = the trait (a genetic disease or abnormality)Y = Y chromosome (males only) Autosomal Dominant Autosomal Recessive Sex-Linked Recessive

  12. Create a Pedigree • Put the male parent to the left of the female. (I generation) • Draw a horizontal line between parents. • Draw a line down from the parents to a horizontal line connecting a group of brothers and sisters. (II generation) • Siblings are entered with the oldest to the left and youngest is to the right. • Draw a line across between a sibling and their spouse. Draw down from this line to their children (grandchildren of I generation). (III generation) • Darken all individuals who are affected. • Mark carriers with a half dark/half light symbol.

  13. Check your understanding What can you conclude about the parents of a person that has a dominant characteristic? (Check the correct answer below.) • --If a person has a dominant trait, the parents will not have the trait. • --If a person has a dominant trait, the parents might have the trait or they might not have it. • --If a person has a dominant trait, at least one of the parents will have the trait. • --If a person has a dominant trait, both of the parents will have the trait. 

  14. Test an Autosomal Dominant • Can two individuals that have an autosomal dominant trait have unaffected children? (Check the correct answer below.) • --If two individuals have a dominant trait, none of their offspring will have the trait. • --If two individuals have a dominant trait, their offspring might or might not have the trait. • --If two individuals have a dominant trait, their offspring will have the trait. Mark the Genotype

  15. What is the pattern? • Label the generations. • Number the people. • Mark the genotypes. • Dominant/Recessive? • Autosomal/Sex-linked? • What is the pattern? ___________________

  16. Dominant or Recessive? Autosomal or Sex-linked? • What is the pattern? _______________ • Trace the lines between IV-4 to the oldest person with the trait.

  17. Dominant or Recessive? Autosomal or Sex-linked? • What is the pattern? _______________ • Label genotypes. Start with the affected individuals.

  18. Dominant or Recessive? Autosomal or Sex-linked? • What is the pattern? _______________ • Which person is the best clue? __________

  19. Resources • McClean, Phillip, 2000, Mendelian Genetics, North Dakota State University, http://www.ndsu.edu/pubweb/~mcclean/plsc431/mendel/mendel9.htm • Tissot, Robert, 2014, Human Genetics, University of Illinois Chicago, http://www.uic.edu/classes/bms/bms655/lesson3.html#Sample

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