Pedigree ChartsPedigree ChartsThe family tree of The family tree of

geneticsgenetics What is a pedigree?What is a pedigree?

Constructing a pedigree Constructing a pedigree

Interpreting a pedigreeInterpreting a pedigree

Some HistorySome History

Hemophilia has played an Hemophilia has played an important role in Europe's important role in Europe's historyhistory

The disease began to The disease began to crop up in Great Britain's crop up in Great Britain's Queen Victoria’s childrenQueen Victoria’s children

It became known as the It became known as the "Royal disease" because "Royal disease" because it spread to the royal it spread to the royal families of Europe families of Europe through Victoria's through Victoria's descendants descendants

How it SpreadHow it Spread

it spread through the it spread through the Royal Houses of Royal Houses of Europe as monarchs Europe as monarchs arranged marriages to arranged marriages to consolidate political consolidate political alliances. alliances.

We can trace the We can trace the appearance of appearance of hemophilia as it popped hemophilia as it popped up in Spain, Russia, up in Spain, Russia, and Prussia by looking and Prussia by looking at the family tree. at the family tree.

The Royal Family TreeThe Royal Family Tree

What is a Pedigree Chart?What is a Pedigree Chart?

A A Pedigree chartPedigree chart traces the inheritance traces the inheritance of a particular trait through several of a particular trait through several generations.generations.

One One GOALGOAL of using a pedigree chart is of using a pedigree chart is to figure out to figure out who are carrierswho are carriers of the of the trait, because this information is typically trait, because this information is typically unknown.unknown.

Steps to Creating a PedigreeSteps to Creating a Pedigree

1.1. A genetic counselor will first gather A genetic counselor will first gather information regarding who the family information regarding who the family members are and how are they related. This members are and how are they related. This will go back a few generations.will go back a few generations.

2.2. The genetic counselor will then ask who has The genetic counselor will then ask who has the trait of interest. (Shows the trait)the trait of interest. (Shows the trait)

3.3. After researching, the genetic counselor uses After researching, the genetic counselor uses all of this information to construct a all of this information to construct a Pedigree Pedigree chartchart, with all the family members’ names and , with all the family members’ names and genotypes written below each symbol.genotypes written below each symbol.

Constructing a PedigreeConstructing a Pedigree

MaleMale

FemaleFemale

Married Couple-Married Couple-– Horizontal LineHorizontal Line

SiblingsSiblings– Vertical lineVertical line

More than one SiblingMore than one Sibling::– a horizontal line is drawn a horizontal line is drawn

with a vertical line coming with a vertical line coming down for each sibling. down for each sibling.

Constructing a PedigreeConstructing a Pedigree

I

II

III

Constructing a PedigreeConstructing a PedigreeRoman numerals to the left of the pedigree show the generations.

Birth Order: children are listed in birth order with oldest on left and youngest on the right.

Fraternal twins-Fraternal twins-– Two line branching from the Two line branching from the

same pointsame point– two eggs and two sperm cells.two eggs and two sperm cells.

Identical twins-Identical twins-– Also called Also called Maternal TwinsMaternal Twins– Identical or Maternal Twins (first Identical or Maternal Twins (first

set above) are drawn branching set above) are drawn branching off of the same point, off of the same point, butbut are are also connected to each otheralso connected to each other

Constructing a PedigreeConstructing a Pedigree

More Symbols in a Pedigree ChartMore Symbols in a Pedigree Chart

Full Shaded:Full Shaded:– Affected person who Affected person who

shows a disordershows a disorder Half shaded:Half shaded:

– Autosomal carrierAutosomal carrier Circle with dotCircle with dot::

– X-linked carrier –always X-linked carrier –always femalefemale

DeceasedDeceased

Sex-Linked TraitsSex-Linked Traits

Genes located on the X chromosomes (some Genes located on the X chromosomes (some cause diseases)cause diseases)

The Y is much smaller, contains few genesThe Y is much smaller, contains few genes Sex Linked DisordersSex Linked Disorders

– Color Blindness (red-green)Color Blindness (red-green)– Hemophilia ("bleeders disease)Hemophilia ("bleeders disease)– Duchenne Muscular Dystrophy (weakening/loss of Duchenne Muscular Dystrophy (weakening/loss of

skeletal muscles)skeletal muscles)

More common for males to display disordersMore common for males to display disorders

Sex-Linked TraitsSex-Linked Traits

Consider hemophiliaConsider hemophilia

How do you find the How do you find the genotypesgenotypes of the of the persons in the chart?persons in the chart?

Start with the person showing the trait.Start with the person showing the trait. Look at parents of this individual and ask Look at parents of this individual and ask

yourself: what would the parent’s yourself: what would the parent’s genotypes have to be (in a Punnett genotypes have to be (in a Punnett square) to produce an offspring with this square) to produce an offspring with this genotype? genotype?

If there is not enough information to If there is not enough information to figure out the entire genotype then a figure out the entire genotype then a question mark is used to take the place question mark is used to take the place of the uncertain allele. Ex. of the uncertain allele. Ex. T?T?

Is Is deafnessdeafness a dominant or a dominant or recessive trait?recessive trait?

To show deafness, what To show deafness, what genotype does this son have genotype does this son have to have? to have?

For two parents who have For two parents who have normal hearing to have a deaf normal hearing to have a deaf son, they both must be son, they both must be carrier. What are the parent carrier. What are the parent genotypes?genotypes?

Example ProblemExample Problem

Shaded=deaf

(D) is normal hearing

(d) is deafrecessive

dd

Dd

Write the genotypes for the parents and son Write the genotypes for the parents and son under the correct circle/boxes, half-shading under the correct circle/boxes, half-shading carriers.carriers.

Example ProblemExample Problem

Shaded=deaf

(D) is normal hearing

(d) is deaf

Dd Dd

dd

Pedigrees are used to find out:Pedigrees are used to find out:– who are carriers of the disorder &who are carriers of the disorder &– the probability of having a future child with the probability of having a future child with

the disorder.the disorder.

To begin to interpret a pedigree, first To begin to interpret a pedigree, first determine if the disorder is:determine if the disorder is:– Autosomal dominant Autosomal dominant – Autosomal recessiveAutosomal recessive– Sex-linked (carried on the Sex-linked (carried on the X X chromosome)chromosome)

Predicting using Pedigree ChartsPredicting using Pedigree Charts

Interpreting a Pedigree ChartInterpreting a Pedigree Chart

First ask: First ask: Is it a Sex-linked or Autosomal Disorder?Is it a Sex-linked or Autosomal Disorder?

– If there is a If there is a much larger number of much larger number of malesmales than females who are affected than females who are affected then the disorder is then the disorder is Sex-linkedSex-linked..

– If there is a If there is a 50/50 ratio between males 50/50 ratio between males and femalesand females who are affected then the who are affected then the disorder is disorder is autosomalautosomal..

Interpreting a Pedigree ChartInterpreting a Pedigree Chart

If it is autosomal disorder then ask:If it is autosomal disorder then ask:Is it dominant or recessive?Is it dominant or recessive?

– If two parents do not show the trait If two parents do not show the trait and their children do show it, then it is and their children do show it, then it is an an autosomal recessiveautosomal recessive disorder disorder (parents are heterozygous)(parents are heterozygous)

– If the disorder is If the disorder is autosomal autosomal dominantdominant, then at least one of the , then at least one of the parents must show the disorder.parents must show the disorder.

Note:Note:

The following pedigree charts show infected The following pedigree charts show infected individuals only. individuals only.

Carriers are unknown at this point.Carriers are unknown at this point.

Practice ExamplesPractice Examples

Does this pedigree show a Does this pedigree show a Sex-linkedSex-linked or or AutosomalAutosomal disorder? disorder?

Answer:Answer:

Sex-Linked Disorder Sex-Linked Disorder much larger number of males are affectedmuch larger number of males are affected

Practice ExamplesPractice Examples

Does this pedigree show a Does this pedigree show a Sex-linkedSex-linked or or AutosomalAutosomal disorder? disorder?

Answer:Answer:

Autosomal Disorder Autosomal Disorder 50/50 ratio between males and females50/50 ratio between males and females

Practice ExamplesPractice Examples

Does this pedigree show a Does this pedigree show a AutosomalAutosomal Dominant or RecessiveDominant or Recessive disorder? disorder?

Answer:Answer:Autosomal DominantAutosomal Dominant Disorder Disorder

At least one parent of the affected At least one parent of the affected children show the disorderchildren show the disorder

Practice ExamplesPractice Examples

Does this pedigree show a Does this pedigree show a Sex-linkedSex-linked or or AutosomalAutosomal disorder? disorder?

Answer:Answer:

Autosomal Disorder Autosomal Disorder 50/50 ratio between males and females50/50 ratio between males and females

Practice ExamplesPractice Examples

Does this pedigree show a Does this pedigree show a AutosomalAutosomal Dominant or RecessiveDominant or Recessive disorder? disorder?

Answer:Answer:Autosomal RecessiveAutosomal Recessive Disorder Disorder

Two parents do not show the trait and their Two parents do not show the trait and their children do show it (heterozygous parents)children do show it (heterozygous parents)

dddd dd dd

dddd

Dd Dd Dd Dd

Autosomal RecessiveAutosomal Recessive Genotypes and Carrier determinationGenotypes and Carrier determination

D = Normal hearingD = Normal hearing d = deafness d = deafness

Dd

Dd

D?