Pedigree ChartsPedigree Charts

The family tree of geneticsThe family tree of genetics

What is a Pedigree?What is a Pedigree?

A pedigree is a chart of the genetic history A pedigree is a chart of the genetic history of family over several generations.of family over several generations.

A pedigree shows the presence or absence A pedigree shows the presence or absence of a trait according to the relationships of a trait according to the relationships between parents, siblings, and offspring. between parents, siblings, and offspring.

What does a Pedigree SHOW?What does a Pedigree SHOW?

Whether a trait is inheritedWhether a trait is inherited

How a trait is passed from one generation to How a trait is passed from one generation to the nextthe next

Whether an allele is dominant or recessiveWhether an allele is dominant or recessive

Constructing a PedigreeConstructing a Pedigree

MaleMale

FemaleFemale

Connecting Pedigree SymbolsConnecting Pedigree Symbols

Married CoupleMarried Couple

SiblingsSiblings

Examples of connected symbols:Examples of connected symbols:

Symbols in a Pedigree ChartSymbols in a Pedigree Chart

AffectedAffected CarrierCarrier DeceasedDeceased

Pedigree SymbolsPedigree Symbols

Roman Numerals represent generationsRoman Numerals represent generations

II

IIII

IIIIII

Interpreting a Pedigree ChartInterpreting a Pedigree Chart

1.1. Determine if the pedigree chart shows an autosomal or X-linked disease.Determine if the pedigree chart shows an autosomal or X-linked disease.

– If most of the males in the pedigree are affected the disorder is X-linked If most of the males in the pedigree are affected the disorder is X-linked

X-linked RecessiveX-linked Recessive

a.a. Affected male children MUST have a heterozygous motherAffected male children MUST have a heterozygous mother

b.b. An affected female WILL transmit the trait to ALL male childrenAn affected female WILL transmit the trait to ALL male children

X-linked DominantX-linked Dominant

a.a. Affected males transmit the trait to ALL daughtersAffected males transmit the trait to ALL daughters

b.b. Affected some MUST have an affected motherAffected some MUST have an affected mother

– If it is a 50/50 ratio between men and women the disorder is autosomal.If it is a 50/50 ratio between men and women the disorder is autosomal.

Example of Pedigree ChartsExample of Pedigree Charts

Is it Autosomal or X-linked?Is it Autosomal or X-linked?

AnswerAnswer

AutosomalAutosomal

Interpreting a Pedigree ChartInterpreting a Pedigree Chart

2.2. Determine whether the disorder is Determine whether the disorder is dominant or recessive.dominant or recessive.

– If the disorder is dominant, one of the If the disorder is dominant, one of the parents must have the disorder.parents must have the disorder.

– If the disorder is recessive, neither If the disorder is recessive, neither parent is affected because they can be parent is affected because they can be heterozygous for the disorder.heterozygous for the disorder.

Example of Pedigree ChartsExample of Pedigree Charts

Dominant or Recessive?Dominant or Recessive?

AnswerAnswer

DominantDominant

Example of Pedigree ChartsExample of Pedigree Charts

Dominant or Recessive?Dominant or Recessive?

AnswerAnswer

RecessiveRecessive

TraitsTraits

DominantDominant Passed on to a child from Passed on to a child from

only 1 parentonly 1 parent Every affected individual Every affected individual

has at least 1 affected has at least 1 affected parentparent

2 affected individuals 2 affected individuals CAN have unaffected CAN have unaffected childrenchildren

RecessiveRecessive Passed on to a child from Passed on to a child from

BOTH parentsBOTH parents An individual who is An individual who is

affected many have affected many have parents who are parents who are unaffectedunaffected

All children of 2 affected All children of 2 affected individuals are affectedindividuals are affected

SummarySummary

Pedigrees are family trees that Pedigrees are family trees that explain your genetic history.explain your genetic history.

Pedigrees are used to find out the Pedigrees are used to find out the probability of a child having a probability of a child having a disorder in a particular family.disorder in a particular family.

Human PedigreesHuman Pedigrees

– This diagram shows what the symbols in a This diagram shows what the symbols in a pedigree represent. pedigree represent.

Human PedigreesHuman Pedigrees

– This pedigree shows how one human traitThis pedigree shows how one human trait—a white lock of hair just above the forehead——a white lock of hair just above the forehead—passes through three generations of a family. passes through three generations of a family.

– The allele for the white forelock trait is The allele for the white forelock trait is dominant. dominant.

Human PedigreesHuman Pedigrees

– At the top of the chart is a grandfather At the top of the chart is a grandfather who had the white forelock trait. who had the white forelock trait.

– Two of his three children inherited the Two of his three children inherited the trait. trait.

– Three grandchildren have the trait, but two Three grandchildren have the trait, but two do not.do not.

Human PedigreesHuman Pedigrees

– Because the white forelock trait is Because the white forelock trait is dominant, all the family members in the dominant, all the family members in the pedigreepedigree lacking this trait must have lacking this trait must have homozygous recessive alleles. homozygous recessive alleles.

– One of the grandfather’s children lacks One of the grandfather’s children lacks the white forelock trait, so the grandfather must the white forelock trait, so the grandfather must be heterozygous for this trait.be heterozygous for this trait.