Pedigrees and Modes of Inheritance

Pedigree

A diagram of family relationships that uses symbols to represent people and lines to represent genetic relationships.

Modes of Inheritance (MOI)

The ways in which traits are passed from parents to offspring.

Autosomal Recessive

A mode of inheritance where traits are passed on from parents to offspring and examples include Cystic fibrosis and Sickle cell anaemia.

Autosomal Dominant

A mode of inheritance where traits are passed on from parents to offspring and examples include Retinoblastoma.

X-Linked Recessive

A mode of inheritance where traits are passed almost exclusively on the X chromosome, with Duchenne Muscular Dystrophy as an example.

X-Linked Dominant

A mode of inheritance where traits are passed almost exclusively on the X chromosome, with Rett Syndrome as an example.

Autosomal Traits

Traits that are passed on from parents to offspring independent of the X and Y chromosomes.

X-Linked Traits

Traits that are almost exclusively passed on the X chromosome.

Normal Allele

The allele that does not cause a genetic disease, represented as A+.

Disease Allele

The allele that causes a genetic disease, represented as A-.

Inbreeding

The mating of individuals who are closely related, which can increase the risk of genetic diseases.

Consanguinity

The sharing of blood or genetic material between individuals.

Homozygous

Having two identical alleles for a particular gene.

Heterozygous

Having two different alleles for a particular gene.

Autosomal Dominant Trait

Normal: A-A-, Affected: A+A+ or A+A-.

Autosomal Recessive Trait

Normal: A+A+ or A+A-, Affected: A-A-.

X-Linked Dominant Trait

Normal: XA-XA- or XA-Y, Affected: XA+XA+ or XA+XA- or XA+Y.

X-Linked Recessive Trait

Normal: XA+XA+ or XA+XA- or XA+Y, Affected: XA-XA- or XA-Y.

Male to Male Transmission

Transmission of traits that can only occur through autosomal inheritance.

More than 1 possible MOI

Indicates that additional generations may be needed to determine the correct mode of inheritance.

Obligate Heterozygotes

Individuals who do not show a trait but must carry one allele for it.

Autosomal Hypothesis

A hypothesis that suggests a trait is inherited through autosomal recessive inheritance.

X-Linked Hypothesis

A hypothesis that suggests a trait is inherited through X-linked inheritance.

Albinism

A genetic condition that can be analyzed using all four modes of inheritance.

Pedigree Analysis

The study of family trees to understand the inheritance of traits.

Extra Generation

Additional generations added to a pedigree to clarify modes of inheritance.

Labeling Pedigrees

The process of assigning symbols and explanations to a pedigree.

Research Before Inbreeding

The importance of understanding genetic risks before mating closely related individuals.

Obligate Heterozygote

individual who might be clinically unaffected but must carry the mutant allele based on pedigree analysis

indicates dominance OR indicates recessive:

disease present in every generation.

dominance

indicates dominance OR indicates recessive:

family is outbred

dominance

indicates dominance OR indicates recessive:

family inbred

recessive

indicates dominance OR indicates recessive:

generations skipped

recessive, but data missing