PEDIGREESAnalyzing 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 InheritanceEach type has a distinctive pattern

Autosomal DominantAutosomal RecessiveSex-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 = normalXa = the trait (a genetic disease or abnormality)Y = Y chromosome (males only)

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 = normalXa = the trait (a genetic disease or abnormality)Y = Y chromosome (males only)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 = normalXa = 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 understandingWhat 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.html#Sample