Patterns of Inheritance
This resource contains a set of human pedigrees demonstrating different modes of inheritance. The pedigrees and descriptions here are based on example pedigrees presented in The Human Genome A User's Guide by Dr. Julia Richards, PhD.
Dominant Transmission of Deafness
Dominant transmission of deafness in a hypothetical four-generation family. Each person with the trait passes the trait along to about half of their children, both sexes can have the trait, and both sexes can pass the trait along. Individuals who do not have the trait do not pass deafness along to their descendants. Every time someone deaf in this family has a child, there is a 50% chance that their child will be deaf.
RESULT FILE: Deafness_pedigree.svg
Recessive Transmission of Albinism 1
Albinism family tree. In the first generation, we see two different couples in which an individual with albinism marries someone who does not have the albinism trait. All of their children have pigmented hair and are carriers, individuals who lack the trait but carry the information. Marriage of two carriers results in about one-quarter of their children having the albinism trait.
RESULTS FILE: Albinism_001_pedigree.svg
Recessive Transmission of Albinism 2
A hypothetical albinism pedigree shows what the family history might look like for a family of five generations in which the youngest sibship includes a child with albinism.
RESULT FILE: Albinism_002_pedigree.svg
Blue Eyes in a Scandinavian Family
A Scandinavian family showing inhritance of blue eye color. Inheritance of blue eye color is seen in four generations in a row. Although this family shows some features of dominant inheritance, the proband having two brown-eyed parents and three brown-eyed siblings is more like what we would expect for recessive inheritance. We are assisted in interpreting this pedigree by knowing that blue eyes are quite common in Scandanavian populations and that Scandinavian populations have a high carrier rate for the BEY2 allele for blue eyes. This family shows so many blue-eyed individuals because the carrier rate in the population is so high, so many people who marry into the family are carriers. The actual inheritance of of eye color is more complex than this. There are additional genes involved in eye color, and the "brown" phenotype varies, including different shades of brown as well as some mixed colors such as hazel or blue with brown spots.
RESULT FILE: Scandinavian_Blue_Eyes_pedigree.svg
Nail Patella Syndrome
Transmission of the "no nail" phenotype through four generations in a nail-patella syndrome family. As you can see, inheritance is dominant with a 50% risk of passing along an affected allele to the next generation. Both sexes are affected and both sexes can pass along the trait. Unaffected indivudals do not appear to pass nail-patella syndrome along to their children.
Large family showing mitochondrial inheritance of sensorineural hearing loss. Only four generation are shown from a larger family. In the larger overall family, 18 of 34 children of affected mothers were affected, but there were no affected individuals among the 22 family members who had affected fathers.
RESULT FILE: Mitochondrial_Hearing_Loss_pedigree.svg