1. Chart that shows genetic connections among individuals
Pedigrees
Chart that shows genetic connections among individuals
The knowledge of Mendelian patterns is used to suggest basis of inheritance for a trait
Uses standardized symbols so that everyone understands what is being shown

2. symbol
definition
female
male
mating between male & female
mating with no children
monozygotic twins [identical]
dizygotic twins [non-identical]

3. symbol
definition
affected individuals
carrier for autosomal trait [often not shown]
carrier for sex-linked trait [often not shown]
offspring of unknown gender x
‘x’ offspring of the same gender
individual died prematurely

4. Types of pedigrees
By analyzing a pedigree you can determine the type of inheritance for the trait.
Traits are either dominant or recessive.
Traits are either on the X chromosome or they are autosomal.
examples

5. 1. Autosomal Recessive Inheritance
Features
both unaffected parents of affected individual must be heterozygous I II
III
affected individuals may skip generations
males & females equally affected
father to son transmission possible

6. 1. Autosomal Recessive Inheritance

7. Galactosemia Caused by autosomal recessive allele
Gene specifies a mutant enzyme in the pathway that breaks down lactose
enzyme 1
enzyme 2
enzyme 3
GALACTOSE-1-
PHOSOPHATE
GALACTOSE-1-
PHOSOPHATE
LACTOSE
GALACTOSE
+ glucose
intermediate
in glycolysis

8. 2. Autosomal Dominant Inheritance
Features
half of the children of an affected parent are affected I II
III
trait does not skip generations
males & females equally affected
father to son transmission is possible

9. 2. Autosomal Dominant Inheritance

10. Huntington Disorder Autosomal dominant allele
Causes involuntary movements, nervous system deterioration, death
Symptoms don’t usually show up until person is past age 30
People often pass allele on before they know they have it

11. Acondroplasia Autosomal dominant allele
In homozygous form usually leads to stillbirth
Heterozygotes display a type of dwarfism
Have short arms and legs relative to other body parts
Father and son, both with achondroplasia

12. 3. X-linked inheritance Features more males are affectedII
III
more males are affected
may skip generations
father to son transmission is NOT possible
only females can be carriers

13. 3. X-linked inheritance

14. Examples of X-Linked Traits
Color blindness
Inability to distinguish among some of all colors
Hemophilia
Blood-clotting disorder
1/7,000 males has allele for hemophilia A
Was common in European royal families

15. Fragile X Syndrome An X-linked recessive disorder
Causes mental retardation
Mutant allele for gene that specifies a protein required for brain development
Allele has repeated segments of DNA
Brothers, the younger has Fragile-X syndrome.

16. Hutchinson-Guilford Progeria
Mutation causes accelerated aging
No evidence of it running in families
Appears to be dominant
Seems to arise as spontaneous mutation
Usually causes death in early teens

17. Determining inheritance patterns based on pedigrees

18. Therefore is autosomal dominant.
What type of inheritance?
1. Are both genders affected equally?
Yes.
Not X-linked
2. Is there any father to son transmission?
Yes.
Not X-linked
No.
3. Does the trait skip generations?
Not recessive
Therefore is autosomal dominant.

19. Therefore is Autosomal recessive
What type of inheritance?
1. Are both genders affected equally?
No.
Maybe X-linked
2. Is there any father to son transmission?
Yes.
Not X-linked.
3. Does the trait skip generations?
Yes.
Recessive.
Therefore is Autosomal recessive

20. Therefore this is a autosomal, recessive trait.
What type of inheritance?
1. Are both genders affected equally?
Yes.
Not X-linked
2. Is there any father to son transmission?
Yes.
Not X-linked.
3. Does the trait skip generations?
Yes.
Recessive.
Therefore this is a autosomal, recessive trait.

21. Now, can we determine the genotypes of the individuals in the pedigree?
1. Start with determining the inheritance type.
2. Once we know this, we assign the genotype to the known individuals:
If autosomal dominant trait  the unaffected are aa
If X-linked recessive  the affected males are XaY and the affected females are XaXa
If is autosomal recessive, the affected individuals are aa

22. How do we determine the genotypes of the individuals in this pedigree?
1. Determine inheritance
We just did  it’s autosomal recessive
2. Assign the affected individuals as ‘aa’
3. Any unaffected parent of an ‘aa’ individual must be ‘Aa’

23. Aa aa Aa A_ Aa aa A_