相同

• Reading: そうどう
• Romaji: sodo
• Kanji breakdown: 相 (so) — mutual, corresponding | 同 (do) — same, identical
• Pronunciation: /so.ɯ.do.ɯ/

Meaning

Homologous; corresponding in structure or evolutionary origin, even if function differs. Describes organs or genes sharing a common ancestor.

A key concept in evolutionary biology and genetics. 相同器官 (homologous organs) such as the human arm, bat wing, and whale flipper share skeletal structure from a common ancestor despite different functions — contrasting with 相似器官 (analogous organs) which have similar function but different origin. 相同染色体 (homologous chromosomes) are chromosome pairs inherited from each parent.

Examples

1. 脊椎動物の前肢は、形や機能が異なっても相同器官として分類される。 The forelimbs of vertebrates are classified as homologous organs even when their shape and function differ.
2. ヒトとチンパンジーの遺伝子配列には多くの相同領域が存在し、共通祖先の存在を示唆する。 The gene sequences of humans and chimpanzees contain many homologous regions, suggesting the existence of a common ancestor.
3. 相同染色体は両親から一本ずつ受け継がれ、対になって細胞の核に存在する。 Homologous chromosomes are inherited one from each parent and exist as pairs in the cell nucleus.

Usage Guide

Context: evolutionary biology, genetics, comparative anatomy

Tone: technical

Origin & History

Compound of 相 (so) meaning 'mutual, corresponding' and 同 (do) meaning 'same, identical'. In biological usage, it translates the Greek homos (same) + logos (relation), the root of the English term homologous.

Cultural Context

Era: Meiji–Modern

Generation: Biology students and researchers

Social background: Academic