2. Overview
I. What is a pedigree?
a. Definition
b. Uses
II. Constructing a pedigree
a. Symbols
b. Connecting the symbols
III. Interpreting a pedigree
3. What is a Pedigree?
• A pedigree is a chart of the
genetic history of family
over several generations.
• Scientists or a
genetic counselor
would find out about
your family history
and make this chart
to analyze.
7. Generations
• Individuals in
each generation
may be
numbered or
named.
• Siblings are
placed in birth
order from left to
right.
1 2
1 2 3 4 5 6
1 2 3 4 5
8. Interpreting a Pedigree Chart
1. 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 probably X-linked.
– If it is a 50/50 ratio between men and
women the disorder is probably autosomal.
11. Interpreting a Pedigree Chart
2. Determine whether the disorder is
dominant or recessive.
– If the disorder is dominant, one of the
parents must have the disorder.
– If the disorder is recessive, neither
parent has to have the disorder because
they can be heterozygous.
16. Rules of Inheritance Autosomal Recessive
•Appears in both sexes with equal frequency
• Trait tend to skip generations
• Affected offspring are usually born to
unaffected parents
• When both parents are hetrozygous,
approx. 1/4 of the progeny will be affected
• Appears more frequently among the
children of consanguine marriages
17. • Autosomal Recessive
• Affected individual from unaffected parents
• Expressed in both sexes at approximately
equal frequency: AUTOSOMAL
• Not expressed in every generation.
18. Autosomal Dominant
• Appears in both sexes with equal frequency
• Both sexes transmit the trait to their offspring
• Does not skip generations
• Affected offspring must have an affected parent
unless they posses a new mutation
• When one parent is affected (het.) and the other
parent is unaffected, approx. 1/2 of the offspring
will be affected
• Unaffected parents do not transmit the trait
20. X-linked dominant
• Both males and females are affected; often more
females than males are affected
• Does not skip generations.
• Affected sons must have an affected mother;
• affected daughters must have either an
affected mother or an affected father
• Affected fathers will pass the trait on to all their
daughters
• Affected mothers if heterozygous will pass the
trait on to 1/2 of their sons and 1/2 of their
daughters
21. • X-Linked Dominant
• Every Generation: Dominant
• Father passes on to only daughters
• Mothers passes on to 1/2 of offspring
22. X-Linked Recessive
• More males than females are affected
• Affected sons are usually born to
unaffected mothers, thus the trait skips
generations
• Approximately 1/2 of carrier mothers’ sons
are affected
• It is never passed from father to son
• All daughters of affected fathers are
carriers
23. X-linked recessive
•Hemophilia
•Only males are affected and sons do not share the
phenotype of their father - Thus X-linked
•Expression of hemophilia skips generations:
RECESSIVE
24. Y-Linked Dominant
• Only males are affected
• It is passed from father to all sons
• It does not skip generations
25. Y linked dominant
• Y-linked infertility
• Absent or abnormal testicular
development
• Retinitis pigmentosa—abnormal protein
development in eye, hence sight is
degenerated over time ending in severe
vision impaireness and often blindness
27. 1. This pedigree shows the inheritance of attached earlobes. Which parent
has attached ear lobes?
The father
2. How many children do the parents have? Which child has attached ear
lobes?
3 children, Child #1 has attached ear lobes.
3. Which child is married? Does the spouse have attached ear lobes?
Child # 3 is married. Her spouse does not have attached earlobes.
4. Do any of this child’s children have attached ear lobes?
Yes, the son has attached earlobes.
28. What does this pedigree chart show?
• How many people are unaffected “carriers”?
• How many people are affected by the disorder?
• How many carriers are female?
29. What does this pedigree chart show?
• How many people are unaffected “carriers”?
• How many people are affected by the disorder?
• Can we tell if the disorder is dominant or
recessive?
• How many generations are represented?
