Inheritance patterns

Traits based on a single gene follow recognizable patterns: autosomal dominant, autosomal recessive, X-linked and mitochondrial. The pattern is read from a pedigree, that is who is affected across generations and sexes. Most common traits, by contrast, are polygenic and follow no simple pattern.

INHERITANCE PATTERNS · PEDIGREES Autosomal dominant one affected parent, both sexes Autosomal recessive healthy carrier parents, child affected X-linked recessive sons affected, mother a carrier Mitochondrial mother passes it to all children Square: man. Circle: woman. Filled: affected. Dot: carrier.

The four classic patterns

Autosomal dominant: an affected parent passes the trait on to half the children on average, regardless of sex. Autosomal recessive: two healthy carriers can have an affected child, the trait seems to skip generations. X-linked recessive: men with only one X are affected more often, women are often only carriers. Mitochondrial: only mothers pass it on, but then to all children.

Reading the pedigree

In a pedigree a square stands for a man, a circle for a woman; filled means affected, half filled a carrier. From the distribution across generations the pattern becomes visible: if the trait appears in every generation, that points to dominant. If it occurs sporadically with healthy parents, to recessive. If almost only men are affected, to X-linked.

Why most traits are more complex

The clear patterns hold for traits determined by a single gene. Most common characteristics and widespread diseases are multifactorial: many genes with a small contribution act together with environment and lifestyle. Here there is no simple square but a probability distribution that polygenic scores try to capture.

What Genome measures. Genome shows genotypes, not family trees. The inheritance pattern of a gene helps to understand what a genotype can mean for relatives too.

Related topics

Dominant and recessiveChromosomes and karyotypemtDNA haplogroupsPenetrance and expressivityGWAS and polygenic scores

Sources

  1. 1Amberger et al., 2019 OMIM.org: leveraging knowledge across phenotype-gene relationships. Nucleic Acids Research 47:D1038–D1043. doi.org/10.1093/nar/gky1151
  2. 2Bamshad et al., 2011 Exome sequencing as a tool for Mendelian disease gene discovery. Nature Reviews Genetics 12:745–755. doi.org/10.1038/nrg3031