Homology

Homology is similarity between biological structures, genes, or other traits because they were inherited from a common ancestor. Homologous traits can differ in form and function.

Common descent: The evolutionary process by which lineages inherit traits from shared ancestors. Homologous traits are evidence that the lineages carrying them share ancestry.
Homologous chromosomes: A pair of chromosomes with corresponding genes at the same loci, one inherited from each parent. Chromosome homology is a specific genetic use of shared correspondence.
Comparative anatomy: The study of similarities and differences in the anatomy of different organisms. Anatomical comparisons identify structures whose shared patterns suggest common inheritance.
Vertebrate forelimb: The front limb of a vertebrate, built from a shared pattern of bones that varies among species. Its corresponding bones remain recognizable in arms, wings, flippers, and other limbs.
Evolutionary developmental biology: The study of how changes in development produce evolutionary changes in organismal form. Comparing developmental processes can reveal how inherited structures were modified.
Orthology: A relationship between homologous genes whose divergence traces to a speciation event. It names the common-ancestry relationship between genes in different species.
Phylogenetics: The study of evolutionary relationships among organisms or genes. Homologous characters provide evidence for reconstructing evolutionary trees.
Hox genes: A family of genes that helps specify the body plan along the head-to-tail axis in animals. Their conserved sequences and developmental roles illustrate homology across animal lineages.
Gene duplication: The creation of an extra copy of a gene within a genome. Duplicated genes can diverge while retaining homology through their shared ancestral copy.
Paralogy: A relationship between homologous genes whose divergence traces to gene duplication. It distinguishes duplicated gene relatives from genes separated by speciation.

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