When completing this pedigree with autosomal dominant inheritance, individuals that are non-shaded are expressing the recessive phenotype and have a genotype of “rr”. Use this knowledge and additional knowledge about how genes are passed from generation to generation to complete the remainder of the pedigree. Shaded individuals will either have a genotype of “Rr” or “R-“ (“RR” or “Rr”, not enough information to determine).
Patterns for Autosomal Dominant Inheritance
After filling in the genotypes for individuals in several family trees that exhibit this mode of inheritance, some patterns that can be noticed are:
- Males and females are equally likely to have the trait.
- There is male to male transmission.
- Traits do not skip generations (generally). If the trait is displayed in offspring, at least one parent must show the trait.
- If parents don’t have the trait, their children should not have the trait (except for situations of gene amplification).
- The trait is present whenever the corresponding gene is present (generally). If both parents possess the trait, but it is absent in any of their offspring, then the parents are both heterozygous (“carriers”) of the recessive allele.
- Homozygotes for the dominant condition have a more severe form of the condition.
Real examples: Sudden Cardiac Death of the Young/Long QT Syndrome (has a recessive and dominant form; recessive is associated with profound deafness), Tuberous Sclerosis Complex, Marfan Syndrome, Neurofibromatosis and Polycystic Kidney Disease.
- Genes act in pairs, one from each parent.
- Gene pairs separate during meiosis and the formation of the sex cells along with the chromosomes.
- When the sperm fertilizes the egg, the father’s genes (and chromosomes) join the mother’s, or both contribute to the genetic makeup of the offspring.
- One form of a gene may be dominant over another form which is recessive and the dominant form would be expressed.