4: Pedigree Analysis

Pedigree Chart

a graphic representation of how a trait is passed from parents to offspring

Pedigree Chart

used primarily by genetic counselors by helping couples decide to have children when there is evidence of a genetically inherited disorder in one or both families

CIRCLES are for FEMALES

SQUARES are for MALES

HORIZONTAL LINES connecting a male & a female represent BIOLOGICAL PARENTS

VERTICAL LINE & BRACKETS connect parent to offspring

A shaded circle indicates a person HAS THE TRAIT

A circle or square NOT SHADED represents and individual who does not have the trait

A half-shaded circle or square means an individual is a career of the trait.

HOW TO READ A PEDIGREE CHART

Autosomal Recessive

Autosomal Dominant

X-linked Recessive

X-linked Dominant

Y-linked

5 MODES OF INHERITANCE

Autosomal Recessive

trait is rare in the pedigree

trait often skips generations (hidden in heterozygous carriers)

trait affects males and females equally

Phenylketonuria (PKU)

Cystic Fibrosis

Sickle Cell Anime

Tay-Sachs Disease

Albinism

autosomal recessive diseases

Phenylketonuria (PKU)

buildup of Phenylalanine in the body due to an enzyme deficiency

Phenylketonuria (PKU)

can not convert the amino acid Phenylalanine to Tyrosine due to a mutation

and can lead to brain damage

Cystic Fibrosis

a disease that causes thick, sticky mucus to build up in the lungs, digestive tract, and other areas of the body

Sickle Cell Anime

sickle cells block blood flow to organs, depriving the affected organs of blood

Tay-Sachs Disease

a rare, inherited disorder that leads to destruction of nerve cells in the brain and spinal cord, causing a progressive decline in neurological function

Albinism

a lack of pigment in the skin, hair, and eyes and a deficiency or complete absence of melanin

Autosomal Dominant

the trait is common in the pedigree

trait is found in every generation

affected individual also transmits the trait to about ½ of their children, regardless of sex

Huntington's Disease

Achondroplasia

autosomal dominant diseases

Huntington's Disease

causes nerve cells in the brain to decay over time

Achondroplasia

a skeletal disorder causing dwarfism

X-linked Recessive

the trait is rare in the pedigree

trait might skip generations

males are often affected than females

affected fathers DO NOT pass to their sons

females are carriers (pass from mom to son)

Color Blindness

Hemophilia

x-linked recessive disorders

X-linked Dominant

trait is common in pedigree

affected fathers pass to ALL of their daughters

males and females are equally likely to be affected

X-linked Dominant

are extremely unusual

often, they are lethal (before birth) in males and only seen in females

Incontinentia Pigmenti (skin lesions)

Hypophosphatemia

X-linked Dominant disorders

Y-linked

traits on the Y chromosome are only found in males, never in females

the father's traits are passed down to all the sons

dominance is irrelevant since there is only 1 copy of each Y-linked gene (hemizygous)