CP Biology Genetics Unit Pedigrees CP Biology Genetics Unit

What is a Pedigree? A diagrammatic tool used by geneticists to show the family history of how a trait is inherited. In other words, similar to a family tree but looks at one trait/disorder only.

How is a Pedigree Helpful? Tracing a genetic disorder through a family over several generations. Determining the possibility of a genetic disorder being passed to offspring. Determining the possibility of parents being carriers of a genetic disorder.

What are Carriers? Carriers are heterozygous individuals who carry the recessive gene for the disorder. Carriers do not show symptoms of the disorder. They can pass the allele for the disorder to their offspring.

What can Scientists Determine from a Pedigree? If the trait is dominant or recessive If the trait is heterozygous or homozygous If the disorder is autosomal (carried on an autosome) or if it is sex-linked (carried on the X chromosome)

Autosomal Disorders Remember, an autosome is a non-sex chromosome: chromosome #1 – 22, NOT pair #23 The trait can be dominant or recessive. Dominant – must have parents with the disorder Recessive – heterozygous parents can have offspring with a recessive disorder Example: Cystic Fibrosis (recessive)

Sex-Linked Disorders Most sex-linked disorders are recessive. If a trait is sex-linked, it is seen primarily in males. This is because almost all sex-linked disorders are located on the X chromosome. Since males only have one X chromosome, the trait shows up. Females have two X chromosomes, they can have one dominant (normal) allele and one recessive allele.

How to Construct a Pedigree Horizontal lines indicate matings. Vertical lines indicate offspring, arrange in order of their birth (left to right) Squares = males Circles = females Shaded in boxes = affected individuals