Download Lecture#23 Page 1 BIOLOGY 207

BIOLOGY 207 - Dr. McDermid
Lecture#23: Pedigree Analysis
Readings: Griffiths et al 7th Edition: Ch. 2 pp 40-53
Problems: Griffiths et al 7th Edition: Ch. 2 Tier 1:#5, 7, 8, 14-16, 40, 51, Tier 2: #17, 20a, 22
Concepts:
How do we analyze inheritance patterns in humans?
1. Mendel's experimental methods cannot be applied to humans.
2. Human genetic disease can only really be identified by family studies.
3. Most kinds of hereditary patterns are evident in humans pedigrees.
Mendel's Experimental Methods
1. Controlled genetic crosses
2. Well characterized, inbred, true breeding strains
3. Follow crosses over several generations
4. Many progeny ‡ accurate representation of the results of a cross
They can not be applied to humans
We need to examine heredity in humans because of:
1) Genetic diseases
2) Parent-offspring testing
3) Forensic analysis
4) Risk groups
Hereditary diseases
- An important aspect of medical practice.
- Physicians (human geneticists) construct a family history or
Pedigree
- Search through these matings in hopes of finding informative
crosses
- A history of matings is shown in diagrammatic form.
There is a conventional set of symbols. See Figure 2-16
Male
Female
Mating
Generation
Affected individuals
Propositus (proband)
Consanguineous marriage
Patterns of inheritance in Pedigrees
Autosomal Recessive Inheritance
Characteristics
1) Trait may skip generations
2) Affected offspring generally have normal (but heterozygous)
parents
3) Males and females equally affected
e.g. -
Autosomal Dominant Inheritance
Characteristics:
1) Dominant - must be observed in each generation
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2) Affected individuals (males and females) transmit to 1/2 children, sons and daughters
3) Males and females equally likely to have the trait
e.g. - achondroplasia (dwarfism)
X-linked Recessive Inheritance
Characteristics:
1) Affected males are much more common than affected
females
2) No transmission from father to son
3) Daughters of affected males are carriers (heterozygotes)
4) Trait is transmitted from heterozygous carrier female to 1/2
sons
5) Affected females have affected fathers and carrier mothers
e.g. hemophila, red-green colour blindness
X-linked Dominant Inheritance
Characteristics:
1) Dominant --> must be observed in each generation
2) Female heterozygote transmit their trait to 1/2 their children of
either sex
3) Male affected transmit to all his daughters and no sons
4) Affected females are more common than affected males
5) No transmission from father to son
e.g. hypophosphatemia - a type of vitamin-D resistant rickets
Y-linked Characteristics:
- gene on Y chromosome
- only males affected! (remember females in ZW system)
- affected male transmits to all sons
- affected male does not transmit to daughters
e.g. hairy ear rim Fig 2-33 ???
The pedigree analysis above is simple.
It assumes:
1.- Single gene locus
2.- Simple dominance and recessive alleles
3.- Complete penetrance
- phenotype accurately reflects the genotype
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Lecture notes: Copyright © 2002 Heather McDermid and the Department of Biological Sciences, University of Alberta
Images are Copyright©2000 by W.H. Freeman & Co. in Griffiths et al, Introduction to Genetic Analysi
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