PEDIGREE CHARTS A family history of a genetic condition or trait

W HAT IS A PEDIGREE CHART ? Pedigree charts show a record of the family of an individual. They can be used to study a hereditary condition or trait. They are especially useful when there are large families that cover several generations. © 2007 Paul Billiet ODWSODWS

S TUDYING HUMAN GENETICS Today genetic engineering has new tools to offer doctors studying genetic diseases A genetic counselor will still use pedigree charts to help determine the distribution of a disease in an affected family © 2007 Paul Billiet ODWSODWS

READING A PEDIGREE CHART Generations are identified by Roman numerals & are on different levels. I II III IV

Males are represented by the square Females are represented by the circle I II III IV

Parents are connected with a horizontal line. Offspring are below the parents and the bracket is connected by a vertical line. Siblings are within the same bracket. Affected individuals (those that show the trait) are shaded. Unaffected individuals (those that do not show the trait) are blank.

READING THE SYMBOLS USED IN PEDIGREE CHARTS Normal male Affected male Normal female Affected female Marriage A marriage with five children, two daughters and three sons. The eldest son is affected by the condition. Eldest child  Youngest child

Genetic Counselors use a pedigree chart to predict the probability of transmitting an inherited disorder.

Sex-linked traits are carried on sex chromosomes (X or Y). Example: Colorblindness which is carried on the X chromosome. Autosomal traits are carried on non-sex chromosomes.

Autosomal recessive Trait is carried on a non-sex chromosome. Trait is rare in pedigree. Trait often “skips” generations (hidden in heterozygous carriers). Affects males and females equally. Example: Cystic fibrosis

Autosomal dominant Trait is carried on a non-sex chromosome. Trait is common in the pedigree. Trait is found in every generation Affected individuals transmit the trait to about ½ their children, regardless of sex. Example: Huntington’s Disease

X-linked recessive Trait is carried X chromosome. Trait is rare in pedigrees and “skips” generations. Affected fathers DO NOT pass trait to their sons. Males are affected more often than females. Example: Colorblindness; Hemophilia

X-linked recessive disorder: Hemophilia in European royalty

X-linked dominant Trait is carried X chromosome. Trait is common in pedigrees. Affected fathers pass trait to ALL of their daughters. Males and females are equally affected. Extremely unusual; often lethal in males (before birth) and only seen in females.

#1) Let’s try to figure out some together! Is this trait autosomal or sex-linked? Is this trait dominant or recessive? Answer: autosomal dominant  Each affected individual has an affected parent; no skipping generations; normal siblings of affected individuals have all normal children; males and females are affected equally; about ½ the offspring of an affected individual are affected.

#2) Let’s try to figure out some together! Is this trait autosomal or sex-linked? Is this trait dominant or recessive? Answer: X-linked recessive  Affected males do not pass trait to any of their sons; skips a generation; female carriers can produce sons with trait; more likely to affect males than females.

#3) Let’s try to figure out some together! Is this trait autosomal or sex-linked? Is this trait dominant or recessive? Answer: autosomal recessive  affects males and females equally; rare in pedigree; often skips generations.