L29: Pedigrees

What are pedigrees used to determine

Modes of Inheritence

What is a pedigree

A diagram of family relationships which uses:

• Symbols = people

• Lines = Genetic Relationships

Symbols used for Males in Pedigrees

Square

Symbol used for females in pedigrees

Circle

Line used for Mating in pedigrees

Horizontal

Lines used for offspring in pedigrees

Vertical

What does a diagonal line through a symbol show on a pedigree

That person is deceased

What can we determine about traits from pedigrees

If the gene for a given trait is on an autosome or sex chromosome

How are autosomal traits passed

From parents to offspring independent of the X and Y chromosomes

What is important about X linked traits

Almost exclusively passed on the X chromosome which determines if an individual is XX or XY

What are the 4 possible modes of inheritance

1. Autosomal Recessive

2. Autosomal Dominant

3. X linked Recessive

4. X linked Dominant

MOI of Cystic fibrosis and Sickle cell anaemia

Autosomal Recessive

MOI of Retinoblastoma

Autosomal dominant

MOI of Duchenne Muscular Dystrophy

X linked Recessive

MOI of Rett syndrome

X linked dominant

What should you never assume about pedigrees

That parents are homozygous

square symbol

males

circle symbols

females

shaded square or circle

represents individual affected by the trait being studied

unshaded square or circle

represents unaffected individual

half shaded square or circle

represents a carrier of a recessive trait

diamond

gender unknown/unspecified

how are siblings connected

a horizontal line above their symbols

Describe autosomal recessive inheritance

• affected gene is located on one of the autosomes

• 2 copies of the mutated gene are required for individual to be affected

• carriers have one normal and one mutated allele but do not show symptoms

• affected individuals often have unaffected parents who are both carriers

• males and females equally affected

• often skips generations

• if both parents are carriers, there is a 25% chance the child will be affected

Describe autosomal inheritance

• affected gene located on one of the autosomes

• only one mutated copy of gene is needed to show symptoms

• affected person usually has at least one affected parent

• males and females equally affected

• no carriers

• does not skip generations

• affected individuals have a 50% chance of passing it to offspring

describe x-linked recessive inheritance

• affected gene is on X chromosomes

• males more affected

• females usually carriers

• fathers can only pass trait onto daughters

describe x linked dominant traits

• affected gene of X chromosome

• only one mutated copy needed to show symptoms

• males and females can be affected but females more commonly

• fathers cannot pass to sons

• any daughter with affected father will be affected

• in every generation