Analyzing family relationships for genetic clues 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: To determine the mode inheritance of a genetic disease. To estimate the risk of passing on a genetic disease.

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

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

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

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?

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

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 Xc Xc

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 = normal Xa = the trait (a genetic disease or abnormality) Y = Y chromosome (males only) Autosomal Dominant Autosomal Recessive Sex-Linked Recessive

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

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

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.

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. 

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

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

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

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

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

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.h tml#Sample