Pedigree Part 1

• Record of the family of an individual

• Can be used to study the transmission of a hereditary condition

PEDIGREE ANALYSIS

• Useful in large families

• Shows traits over several generations

PEDIGREE ANALYSIS

Normal appearance of genetically controlled traits in the phenotype.

Penetrance

The degree of expression of a genetically controlled trait.

Expressivity

Determines whether the gene is expressed or not.

Penetrance

Determines how much the trait affects or how many features of the trait appear in person.

Expressivity

When 100% of individuals with the genotype express the associated trait.

Complete Penetrance

When some individuals with the genotype do not show the expected phenotype. (50%)

Incomplete Penetrance

When all individuals with the genotype show the trait to the same degree.

Constant Expressivity

When individuals with the same genotype show the phenotype with different severity or forms.

Variable Expressivity

• A phenotype not genetically determined but looks like a genetically controlled phenotype

• Environmental exposure

Phenocopy

What are situations that show Phenocopy?

• Thalidomide exposure causes phocomelia

• Gestational Zika virus infection in the mother may cause microcephaly

Under Family Tree what does the Following mean?

Shapes

• Squares:

• Circle:

Shapes

• Squares: males

• Circle: females

Under Family Tree what does the Following mean?

Lines

• Horizontal:

• Vertical:

• Diagonal:

Lines

• Horizontal: marriage

• Vertical: offspring

• Diagonal: death

Under Family Tree what does the Following mean?

Filling

• Shaded:

• Partially shaded:

• No shade:

Filling

• Shaded: with trait

• Partially shaded: carrier

• No shade: without trait

Under Family Tree what does the Following mean?

Numbers

• Roman numerals:

• Numbers:

Numbers

• Roman numerals: generations

• Numbers: birth order

1. Every affected child has an affected parent; no generations are skipped

2. Trait occurs about equally in both sexes

3. When an affected person mates with an unaffected person, approximately 50% of their offspring should be affected

Autosomal Dominant Inheritance

Examples of Autosomal Dominant Inheritance

• Polydactyly

• Huntington disease

• Neurofibromatosis

• Polycystic kidney disease

• Progeria

1. Traits often skip generations

2. Trait occurs about equally in both sexes

Autosomal Recessive Inheritance

3. Commonly seen in consanguineous matings.

4. If both parents are affected, all children should be affected.

Autosomal Recessive Inheritance

5. When an affected person mates with an unaffected person, all offspring are unaffected.

6. Most affected individuals have unaffected parents.

Autosomal Recessive Inheritance

Examples of Autosomal Recessive Inheritance

• Cystic fibrosis

• Sickle cell anemia

• Tay-sachs disease

1. Traits does not skip generations

2. Affected males result from affected mothers.

3. Approx. half the children of an affected heterozygous female are affected.

Sex-linked Dominant Inheritance

4. Affected females come from affected mothers/fathers.

5. All the daughters but none of the sons of an affected father are affected.

Sex-linked Dominant Inheritance

1. Traits may skip generations

2. Most affected individuals are male.

3. Affected males result from affected/carrier mothers.

4. Affected females come from affected fathers and affected/carrier mothers.

Sex-linked Recessive Inheritance

5. Sons of affected females should be affected.

6. Approximately half the sons of carrier females should be affected.

Sex-linked Recessive Inheritance