Pedigree ChartsThe family tree of genetics

What is a pedigree?

Constructing a pedigree

Interpreting a pedigree

What is a Pedigree Chart?1. A Pedigree chart traces the inheritance of a

particular trait through several generations.

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

a. Carrier: someone who is heterozygous for a trait.

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Constructing a Pedigree

Male

Female

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1. Mated Pair:– Horizontal Line

2. Children: - Vertical line

3. More than one child:– a horizontal line is drawn

with a vertical line coming down for each sibling.

Constructing a PedigreeSlide # 4

1. Fraternal twins- can be the same or different gender

a. Two line branching from the same point

b. two different eggs and two different sperm cells.

2. Identical twins-always same gender

a. Also called maternal twins

b. Same as fraternal twins but a horizontal line is added.

c. One egg and one sperm unite and later split to create two babies

Constructing a PedigreeSlide # 5

I

II

III

Generations1. Roman numerals to the left of the pedigree show the generations.

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

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More Symbols in a Pedigree Chart

1. Full Shaded:a. Affected person who

shows a disorder2. Half shaded:

– Autosomal carrier 3. Circle with dot:

– X-linked carrier –always female

4. Deceased

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1. Pedigrees are used to find out:

a. who are carriers of the disorder

b. the probability of having a future child with the disorder.

2. To begin to interpret a pedigree, first determine if the disorder is:

a. Autosomal dominant

b. Autosomal recessive

c. Sex-linked (carried on the X chromosome)

Predicting using Pedigree ChartsSlide # 8

Interpreting a Pedigree Chart

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

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

2. If there is a 50/50 ratio between males and females who are affected then the disorder is autosomal.

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Interpreting a Pedigree Chart

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

2. If two parents do not show the trait and their children do show it, then it is an autosomal recessive disorder

- (parents are carriers or heterozygous)

3. If the disorder is autosomal dominant, then at least one of the parents must show the disorder.

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Note:1. The following pedigree charts show affected

individuals only.

2. Carriers are unknown at this point.

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Practice Examples Does this pedigree show a

Sex-linked or Autosomal disorder?

Answer: Sex-Linked disorder much larger number of males are affected

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Practice Examples Does this pedigree show a

Sex-linked or Autosomal disorder?

Answer:Autosomal disorder 50/50 ratio between males and females

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Practice Examples Does this pedigree show a Autosomal

Dominant or Recessive disorder?

Answer:Autosomal dominant disorder At least one parent of the affected children show the disorder

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Practice Examples Does this pedigree show a

Sex-linked or Autosomal disorder?

Answer:Autosomal disorder 50/50 ratio between males and females

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Practice Examples Does this pedigree show a Autosomal

Dominant or Recessive disorder?

Answer:Autosomal recessive disorder Two parents do not show the trait but their children do show it (heterozygous parents)

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dddd dd dd

dddd

Dd Dd Dd Dd

Autosomal Recessive Genotypes and Carrier determinationD = Normal hearing d = deafness

Dd

Dd

D?

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