diff --git a/gerbil-manager-web/src/genetics/genotype.ts b/gerbil-manager-web/src/genetics/genotype.ts
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+++ b/gerbil-manager-web/src/genetics/genotype.ts
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+/**
+ * Genotype representation + canonical serialisation.
+ *
+ * ── SERIALISATION CONTRACT (must match DATA-1 DB storage) ──────────────────
+ *
+ * In-memory / JSON storage shape (source of truth, lossless):
+ *   Genotype = { [locus]: [alleleA, alleleB] }
+ *   e.g. { "A":["A","a"], "C":["C","ch"], "D":["D","D"], "E":["E","E"],
+ *          "G":["G","G"], "P":["P","p"], "Sp":["Sp","sp"], "Re":["re","re"] }
+ *   - Allele pair is stored most-dominant-first (canonical order).
+ *   - Allele symbols are exactly: A a | C cchm ch | D d | E ef e | G g | P p | Sp sp | Re re
+ *
+ * Compact display string (German-breeder convention, human-facing):
+ *   "Aa CC Dd EE GG Pp Spsp rere"  (locus tokens in fixed order A C D E G P Sp Re)
+ *   - Multi-char alleles concatenate as-is, parsed via maximal-munch over the
+ *     known allele set, so "Cch" = [C, ch], "cchmcchm" = [cchm, cchm].
+ *
+ * Partially-unknown genotypes: an allele may be the wildcard "?" meaning
+ * "unknown / any". Wildcards are accepted by the engine (it expands them over
+ * the locus' allele set, weighted uniformly) — see punnett.ts.
+ * ───────────────────────────────────────────────────────────────────────────
+ */
+import {
+  ALLELE_SYMBOLS,
+  ALLELE_TO_LOCUS,
+  LOCI,
+  LOCUS_ORDER,
+  dominanceRank,
+  type LocusKey,
+} from './loci'
+
+export const WILDCARD = '?'
+
+export type AllelePair = readonly [string, string]
+export type Genotype = Readonly<Record<LocusKey, AllelePair>>
+
+/** Order an allele pair most-dominant-first; wildcards sort last. */
+export function canonicalPair(locus: LocusKey, a: string, b: string): AllelePair {
+  const rank = (x: string) => (x === WILDCARD ? Number.MAX_SAFE_INTEGER : dominanceRank(locus, x))
+  return rank(a) <= rank(b) ? [a, b] : [b, a]
+}
+
+function assertAllele(locus: LocusKey, allele: string): void {
+  if (allele === WILDCARD) return
+  if (!LOCI[locus].alleles.includes(allele)) {
+    throw new Error(`Invalid allele "${allele}" for locus ${locus}`)
+  }
+}
+
+/** Build a validated, canonically-ordered Genotype from a partial map. */
+export function makeGenotype(input: Record<LocusKey, AllelePair>): Genotype {
+  const out = {} as Record<LocusKey, AllelePair>
+  for (const locus of LOCUS_ORDER) {
+    const pair = input[locus]
+    if (!pair) throw new Error(`Missing locus ${locus} in genotype`)
+    assertAllele(locus, pair[0])
+    assertAllele(locus, pair[1])
+    out[locus] = canonicalPair(locus, pair[0], pair[1])
+  }
+  return out
+}
+
+/** The wild-type genotype: AA CC DD EE GG PP spsp rere. */
+export function wildType(): Genotype {
+  const out = {} as Record<LocusKey, AllelePair>
+  for (const locus of LOCUS_ORDER) {
+    // Wild-type is homozygous for the most dominant allele, EXCEPT the
+    // marker loci Sp/Re whose wild form is the recessive (unmarked) allele.
+    const alleles = LOCI[locus].alleles
+    const a = locus === 'Sp' || locus === 'Re' ? alleles[alleles.length - 1] : alleles[0]
+    out[locus] = [a, a]
+  }
+  return out
+}
+
+/** Compact display string, e.g. "Aa CC Dd EE GG Pp spsp rere". */
+export function toDisplayString(g: Genotype): string {
+  return LOCUS_ORDER.map((locus) => g[locus][0] + g[locus][1]).join(' ')
+}
+
+/** Stable JSON-storable object (already the in-memory shape; returned as a copy). */
+export function toJSON(g: Genotype): Record<LocusKey, [string, string]> {
+  const out = {} as Record<LocusKey, [string, string]>
+  for (const locus of LOCUS_ORDER) out[locus] = [g[locus][0], g[locus][1]]
+  return out
+}
+
+export function fromJSON(obj: Record<string, [string, string]>): Genotype {
+  return makeGenotype(obj as Record<LocusKey, AllelePair>)
+}
+
+/**
+ * Split a locus token like "Cch" or "cchmcchm" or "Aa" into its two alleles
+ * via maximal-munch over the known allele symbols (longest-first).
+ */
+function splitToken(token: string): [string, string] {
+  const alleles: string[] = []
+  let rest = token
+  while (rest.length > 0) {
+    if (rest.startsWith(WILDCARD)) {
+      alleles.push(WILDCARD)
+      rest = rest.slice(1)
+      continue
+    }
+    const sym = ALLELE_SYMBOLS.find((s) => rest.startsWith(s))
+    if (!sym) throw new Error(`Cannot parse allele token "${token}" at "${rest}"`)
+    alleles.push(sym)
+    rest = rest.slice(sym.length)
+  }
+  if (alleles.length !== 2) {
+    throw new Error(`Token "${token}" did not resolve to exactly two alleles`)
+  }
+  return [alleles[0], alleles[1]]
+}
+
+/**
+ * Parse a display string ("Aa CC Dd EE GG Pp Spsp rere") back into a Genotype.
+ * Tokens may be given in any order; each token must belong to a distinct locus.
+ * Missing loci default to wild-type.
+ */
+export function fromDisplayString(input: string): Genotype {
+  const tokens = input.trim().split(/\s+/).filter(Boolean)
+  const acc = {} as Record<LocusKey, AllelePair>
+  for (const token of tokens) {
+    const [a, b] = splitToken(token)
+    const refAllele = a === WILDCARD ? b : a
+    if (refAllele === WILDCARD) {
+      throw new Error(`Token "${token}" is fully unknown; cannot infer its locus`)
+    }
+    const locus = ALLELE_TO_LOCUS[refAllele]
+    if (!locus) throw new Error(`Unknown allele "${refAllele}" in token "${token}"`)
+    if (acc[locus]) throw new Error(`Locus ${locus} given twice`)
+    acc[locus] = canonicalPair(locus, a, b)
+  }
+  const base = wildType()
+  return makeGenotype({ ...base, ...acc })
+}
+
+export function hasUnknown(g: Genotype): boolean {
+  return LOCUS_ORDER.some((l) => g[l][0] === WILDCARD || g[l][1] === WILDCARD)
+}