Pedigree Analysis: Six
Modes of Inheritance
The inheritance of many
monogenic
(single-gene) traits can be determined
by the analysis of
family trees (
pedigrees)
(
IG1 15.22)
Pedigrees show
relationships
among individuals
Ex.:
Queen
Victoria's pedigree shows genetic inheritance of
Hemophilia A
Six basic
Modes of
Inheritance
Distinguish autosomal
vs sex-linked
conditions
sex (X)
- linked conditions affect predominantly males
autosomal conditions affect male and females equally
1. Autosomal recessive
ex.: Oculocutaneous Albinism
()
Batten Disease (OMIM204200): high
frequency in
PTC
tasting ()
(Homework)
Clues: Condition
is usually rare (allele frequency
is low)
Allele
is usually present in heterozygous genotypes
Condition often occurs in matings
of related individuals
consanguineous
marriage - at least one ancestor in common
"inbreeding" - consanguineous
marriages occur more frequently than expected
Conditions
often "skips generations"
2. Autosomal dominant
ex.:
Achondroplasia ()
Huntington Disease ()
,
Type 5 (
ARVD5)
()
"Newfoundland's
sudden-death riddle resolved" ()
ACHOO syndrome (
) - photic
sneezing
Fatal Familial Insomnia
() - a
prion
disease
Clues: Allele
is usually present in heterozygous genotype
Condition must appear in every
generation
3. X-linked recessive
ex.:
Hemophilia
A ()
Testicular
Feminization Syndrome ()
Red-Green Colour
Deficiency ()
Clues:
Condition occurs predominantly in males
Affected males usually do not have affected offspring
Criss-Cross inheritance: affected
males & females alternate among generations
4. X-linked dominant
ex.:
Hypophosphatemia () (XLH)
Clues:
Affected males always pass
the
condition to daughters
Affected
females
are usually heterozygous
5.
Y-linked