A diagram that represents the biological relationships between an organism and its ancestors is called Pedigrees. This word has been retrieved from the French “pied de grue” (“crane’s foot”) because the branches and lines of a pedigree show resemblance to a thin crane’s leg with its branching toes. It can be used for different animals, such as humans, dogs, and horses. Often, it is used to look at the transmission of genetic disorders.
- Depicts a certain characteristic or disorder in an individual
- Used for a characteristic like having a widow’s peak or attached earlobes or a genetic disorder like colorblindness or Huntington’s disease
- Used to show familial characteristics in humans
- Used to show certain characteristics in animals that are selectively
- Used to identify individuals at risk of familial disease
- Pedigree data is used to inform the clinical management, including referral of individuals at elevated risk for mutation screening and recommending enhanced screening
Pedigrees use a standard set of symbols that make them easier to understand. Males are shown by squares, while females are shown by circles. Parents are connected by horizontal lines, and vertical lines stemming from horizontal lines lead to the symbols for their offspring. The generations are also clearly marked with numbers, with I being the first generation, II being the children of the first generation, and III being the grandchildren.
By analyzing a pedigree, we can find out genotypes, identify phenotypes, and predict how a trait will be passed on in the future. The information from a pedigree makes it possible to determine how certain alleles are inherited: whether they are dominant, recessive, autosomal, or sex-linked.
To start reading a pedigree:
- Determine whether the trait is dominant or recessive. If the trait is dominant, one of the parents must have the trait. Dominant traits will not skip a generation. If the trait is recessive, neither parent is required to have the trait since they can be heterozygous.
- Determine if the chart shows an autosomal or sex-linked (usually X-linked) trait. In autosomal traits, both males and females are equally likely to be affected (usually in equal proportions).
A pedigree is a representation of our family tree. It shows how individuals within a family are related to each other. We can also show which individuals have a particular trait or genetic condition. If we take a pedigree, which we usually try to include at least three generations, we might be able to determine how a particular trait is inherited. Using that information, we might be able to tell the chance that a given individual will have the trait themselves or could pass it on to their children. It’s important when we draw a pedigree that we try to put in as much information as possible.