PEDIGREE ANALYSIS.pdf

Pedigree analysis- Genetics

1. PEDIGREE ANALYSIS

2. •Pedigrees are diagrams that show the relationships
among the members of a family
OR
•It is a family tree/ chart made of symbols & lines that
represent a person’s genetic family history
•In pedigree, symbolsrepresent people & lines
represent genetic relationship
•It is a visual tool for documenting the biological
relationship in families & determine the mode of
inheritance of genetic diseases
•Constructed by medical geneticist / genetic counselors

3. •It is customary to represent males as squares & females
as circles.
•Horizontal line connecting a circle & a square
represents a mating.
•The offspring of the mating are shown beneath the
mates, starting with the first born at the left &
proceeding through the birth order to the right.
•Individuals that have a genetic condition are indicated
by coloring / shading.
•Generations in a pedigree are usually denoted by
Roman numerals& individuals within a generation are
referred to by Arabic numerals following the Roman
numeral

4. Symbols used in the human pedigree analysis

5. Expected patterns for various types of inheritance in
pedigrees
Autosomalrecessive inheritance
•Trait often skips generations.
•An almost equal number of affected males and
females.
•If both parents are affected, all children should be
affected.
•In most cases of unaffected people mating with
affected individuals, all children produced are
unaffected.
•When at least one child is affected (indicating that the
unaffected parent is heterozygous), then approximately
half the children should be affected.
•Most affected individuals have unaffected parents.

7. Autosomaldominant inheritance
•Trait should not skip generations.
•An affected person mating with an unaffected person
should produce approximately 50% affected offspring
(indicating also that the affected individual is
heterozygous).
•The distribution of the trait among sexes should be
almost equal.
•Transmitted by either sex.

8. X-linked (sex-linked) recessive inheritance
•Most affected individuals are male.
•Affected males result from mothers who are
affected or who are known to be carriers
(heterozygotes).
•Affected females come from affected father and
affected or carrier mothers.
•The sons of affected females should be affected.
•Approximately half the sons of carrier should be
affected.

10. X-linked (sex-linked) dominant inheritance
•The trait does not skip generations.
•Affected males must come from affected mothers.
•Approximately half the children of an affected
heterozygous female are affected.
•Affected females come from affected mothers or
fathers.
•All the daughters, but none of the sons, of an affected
father are affected.

11. Y-linked inheritance
•Affects only males.
•Affected males always have an affected father.
•All sons of an affected man are affected.