diff --git a/packages/jbrowse-plugin-apollo/src/LinearApolloDisplay/glyphs/TranscriptGlyph.ts b/packages/jbrowse-plugin-apollo/src/LinearApolloDisplay/glyphs/TranscriptGlyph.ts
index 42795b9db..5821c26e1 100644
--- a/packages/jbrowse-plugin-apollo/src/LinearApolloDisplay/glyphs/TranscriptGlyph.ts
+++ b/packages/jbrowse-plugin-apollo/src/LinearApolloDisplay/glyphs/TranscriptGlyph.ts
@@ -6,7 +6,11 @@ import {
 } from '@jbrowse/core/util'
 import type { ContentBlock } from '@jbrowse/core/util/blockTypes'
 
-import { DuplicateTranscript, MergeTranscripts } from '../../components'
+import {
+  AddCodingSequence,
+  DuplicateTranscript,
+  MergeTranscripts,
+} from '../../components'
 import {
   isCDSFeature,
   isExonFeature,
@@ -201,7 +205,7 @@ function getLayout(display: LinearApolloDisplay, feature: AnnotationFeature) {
 
 function getContextMenuItems(
   display: LinearApolloDisplay,
-  feature: AnnotationFeature,
+  transcript: AnnotationFeature,
 ): MenuItem[] {
   const { changeManager, regions, selectedFeature, session } = display
   const [region] = regions
@@ -215,7 +219,7 @@ function getContextMenuItems(
           'ApolloTranscriptDetails',
           'apolloTranscriptDetails',
           {
-            feature,
+            feature: transcript,
             assembly: currentAssemblyId,
             changeManager,
             refName: region.refName,
@@ -238,7 +242,7 @@ function getContextMenuItems(
                 doneCallback()
               },
               changeManager,
-              sourceFeature: feature,
+              sourceFeature: transcript,
               sourceAssemblyId: currentAssemblyId,
               selectedFeature,
               setSelectedFeature: (feature?: AnnotationFeature) => {
@@ -261,7 +265,7 @@ function getContextMenuItems(
                 doneCallback()
               },
               changeManager,
-              sourceFeature: feature,
+              sourceFeature: transcript,
               sourceAssemblyId: currentAssemblyId,
               selectedFeature,
               setSelectedFeature: (feature?: AnnotationFeature) => {
@@ -273,6 +277,35 @@ function getContextMenuItems(
       },
     },
   )
+  const { children } = transcript
+  if (!children) {
+    return []
+  }
+  const cdsChildren = [...children.values()].filter((child) =>
+    isCDSFeature(child, session),
+  )
+  if (cdsChildren.length === 0) {
+    menuItems.push({
+      label: 'Add coding sequence',
+      onClick: () => {
+        ;(session as unknown as AbstractSessionModel).queueDialog(
+          (doneCallback) => [
+            AddCodingSequence,
+            {
+              session,
+              handleClose: () => {
+                doneCallback()
+              },
+              changeManager,
+              sourceFeature: transcript,
+              sourceAssemblyId: currentAssemblyId,
+              refName: region.refName,
+            },
+          ],
+        )
+      },
+    })
+  }
   return menuItems
 }
 
diff --git a/packages/jbrowse-plugin-apollo/src/components/AddCodingSequence.tsx b/packages/jbrowse-plugin-apollo/src/components/AddCodingSequence.tsx
new file mode 100644
index 000000000..f74a792e7
--- /dev/null
+++ b/packages/jbrowse-plugin-apollo/src/components/AddCodingSequence.tsx
@@ -0,0 +1,255 @@
+/* eslint-disable @typescript-eslint/unbound-method */
+import type {
+  AnnotationFeature,
+  AnnotationFeatureSnapshot,
+} from '@apollo-annotation/mst'
+import { AddFeatureChange } from '@apollo-annotation/shared'
+import type { AbstractSessionModel } from '@jbrowse/core/util'
+import { revcom } from '@jbrowse/core/util'
+import {
+  Button,
+  DialogActions,
+  DialogContent,
+  DialogContentText,
+  FormControl,
+  FormControlLabel,
+  Radio,
+  RadioGroup,
+  TextField,
+} from '@mui/material'
+import ObjectID from 'bson-objectid'
+import React, { useState } from 'react'
+
+import type { ChangeManager } from '../ChangeManager'
+import type { ApolloSessionModel } from '../session'
+import { findLongestOrf } from '../util/sequenceUtils'
+
+import { Dialog } from './Dialog'
+
+interface AddCodingSequenceProps {
+  session: ApolloSessionModel
+  handleClose(): void
+  sourceFeature: AnnotationFeature
+  sourceAssemblyId: string
+  changeManager: ChangeManager
+  refName: string
+}
+
+// Returns the genomic half-open boundary for stitched position `pos`.
+// For strand +1: the inclusive start (min) of the nucleotide.
+// For strand -1: the exclusive end (max) of the nucleotide.
+// Symmetric usage:
+//   plus:  cdsMin = helper(orf[0]), cdsMax = helper(orf[1]+3)
+//   minus: cdsMax = helper(orf[0]), cdsMin = helper(orf[1]+3)
+function stitchedToGenomicBound(
+  pos: number,
+  exons: { min: number; max: number }[],
+  strand: 1 | -1,
+): number {
+  let cum = 0
+  for (const exon of exons) {
+    const len = exon.max - exon.min
+    if (pos <= cum + len) {
+      const off = pos - cum
+      return strand === 1 ? exon.min + off : exon.max - off
+    }
+    cum += len
+  }
+  const last = exons.at(-1)
+  if (!last) {
+    throw new Error('No exons found')
+  }
+  return strand === 1 ? last.max : last.min
+}
+
+export function AddCodingSequence({
+  changeManager,
+  handleClose,
+  refName,
+  session,
+  sourceAssemblyId,
+  sourceFeature,
+}: AddCodingSequenceProps) {
+  const [method, setMethod] = useState<'longest-orf' | 'manual'>('longest-orf')
+  const [minInput, setMinInput] = useState('')
+  const [maxInput, setMaxInput] = useState('')
+  const [errorMessage, setErrorMessage] = useState('')
+
+  async function onSubmit(event: React.FormEvent<HTMLFormElement>) {
+    event.preventDefault()
+    setErrorMessage('')
+
+    let cdsMin: number
+    let cdsMax: number
+
+    try {
+      if (method === 'longest-orf') {
+        const exonParts = sourceFeature.transcriptExonParts.filter(
+          (p) => p.type === 'exon',
+        )
+        if (exonParts.length === 0) {
+          setErrorMessage('No exons found in this transcript')
+          return
+        }
+
+        const backendDriver =
+          session.apolloDataStore.getBackendDriver(sourceAssemblyId)
+        if (!backendDriver) {
+          setErrorMessage('No backend driver found for this assembly')
+          return
+        }
+
+        let stitchedSequence = ''
+        for (const exon of exonParts) {
+          const { seq } = await backendDriver.getSequence({
+            assemblyName: sourceAssemblyId,
+            refName,
+            start: exon.min,
+            end: exon.max,
+          })
+          stitchedSequence += sourceFeature.strand === -1 ? revcom(seq) : seq
+        }
+
+        const orf = findLongestOrf(stitchedSequence)
+        if (!orf) {
+          ;(session as unknown as AbstractSessionModel).notify(
+            'No open reading frame found in this transcript',
+            'error',
+          )
+          handleClose()
+          return
+        }
+
+        const strand = sourceFeature.strand ?? 1
+        if (strand === 1) {
+          cdsMin = stitchedToGenomicBound(orf[0], exonParts, 1)
+          cdsMax = stitchedToGenomicBound(orf[1] + 3, exonParts, 1)
+        } else {
+          cdsMax = stitchedToGenomicBound(orf[0], exonParts, -1)
+          cdsMin = stitchedToGenomicBound(orf[1] + 3, exonParts, -1)
+        }
+      } else {
+        cdsMin = Number(minInput) - 1
+        cdsMax = Number(maxInput)
+      }
+
+      const _id = new ObjectID().toHexString()
+      const addedFeature: AnnotationFeatureSnapshot = {
+        _id,
+        refSeq: sourceFeature.refSeq,
+        min: cdsMin,
+        max: cdsMax,
+        type: 'CDS',
+      }
+      if (sourceFeature.strand) {
+        addedFeature.strand = sourceFeature.strand
+      }
+      const change = new AddFeatureChange({
+        changedIds: [sourceFeature._id],
+        typeName: 'AddFeatureChange',
+        assembly: sourceAssemblyId,
+        addedFeature,
+        parentFeatureId: sourceFeature._id,
+      })
+      await changeManager.submit(change)
+      session.apolloSetSelectedFeature(_id)
+      handleClose()
+    } catch (error) {
+      setErrorMessage(
+        error instanceof Error ? error.message : 'An unknown error occurred',
+      )
+    }
+  }
+
+  const manualError =
+    method === 'manual' &&
+    Boolean(minInput) &&
+    Boolean(maxInput) &&
+    Number(maxInput) <= Number(minInput)
+
+  const submitDisabled =
+    method === 'manual' ? !(minInput && maxInput) || manualError : false
+
+  return (
+    <Dialog
+      open
+      title="Add coding sequence"
+      handleClose={handleClose}
+      maxWidth={false}
+      data-testid="add-coding-sequence"
+    >
+      <form
+        onSubmit={(event) => {
+          void onSubmit(event)
+        }}
+      >
+        <DialogContent style={{ display: 'flex', flexDirection: 'column' }}>
+          <FormControl>
+            <RadioGroup
+              value={method}
+              onChange={(e) => {
+                setMethod(e.target.value as 'longest-orf' | 'manual')
+              }}
+            >
+              <FormControlLabel
+                value="longest-orf"
+                control={<Radio />}
+                label="Calculate longest open reading frame"
+              />
+              <FormControlLabel
+                value="manual"
+                control={<Radio />}
+                label="Manual"
+              />
+            </RadioGroup>
+          </FormControl>
+          {method === 'manual' ? (
+            <>
+              <TextField
+                margin="dense"
+                id="cds-min"
+                label="Min"
+                type="number"
+                fullWidth
+                variant="outlined"
+                value={minInput}
+                onChange={(e) => {
+                  setMinInput(e.target.value)
+                }}
+              />
+              <TextField
+                margin="dense"
+                id="cds-max"
+                label="Max"
+                type="number"
+                fullWidth
+                variant="outlined"
+                value={maxInput}
+                onChange={(e) => {
+                  setMaxInput(e.target.value)
+                }}
+                error={manualError}
+                helperText={
+                  manualError ? '"Max" must be greater than "Min"' : null
+                }
+              />
+            </>
+          ) : null}
+        </DialogContent>
+        <DialogActions>
+          <Button variant="contained" type="submit" disabled={submitDisabled}>
+            Submit
+          </Button>
+          <Button variant="outlined" type="button" onClick={handleClose}>
+            Cancel
+          </Button>
+        </DialogActions>
+      </form>
+      {errorMessage ? (
+        <DialogContent>
+          <DialogContentText color="error">{errorMessage}</DialogContentText>
+        </DialogContent>
+      ) : null}
+    </Dialog>
+  )
+}
diff --git a/packages/jbrowse-plugin-apollo/src/components/index.ts b/packages/jbrowse-plugin-apollo/src/components/index.ts
index a90f0e42a..b12f6de27 100644
--- a/packages/jbrowse-plugin-apollo/src/components/index.ts
+++ b/packages/jbrowse-plugin-apollo/src/components/index.ts
@@ -1,6 +1,7 @@
 export * from './AddAssembly'
 export * from './AddAssemblyAliases'
 export * from './AddChildFeature'
+export * from './AddCodingSequence'
 export * from './AddFeature'
 export * from './ColorFeature'
 export * from './CopyFeature'
diff --git a/packages/jbrowse-plugin-apollo/src/util/sequenceUtils.ts b/packages/jbrowse-plugin-apollo/src/util/sequenceUtils.ts
new file mode 100644
index 000000000..36a4aa0ec
--- /dev/null
+++ b/packages/jbrowse-plugin-apollo/src/util/sequenceUtils.ts
@@ -0,0 +1,29 @@
+const START_CODON = 'ATG'
+const STOP_CODONS = new Set(['TAA', 'TAG', 'TGA'])
+
+export function findLongestOrf(sequence: string) {
+  const starts: [number | null, number | null, number | null] = [
+    null,
+    null,
+    null,
+  ]
+  let longest: [number, number] | undefined
+  for (let start = 0; start < sequence.length - 2; start++) {
+    const codon = sequence.slice(start, start + 3).toUpperCase()
+    const frame = (start % 3) as 0 | 1 | 2
+    if (codon === START_CODON && starts[frame] === null) {
+      starts[frame] = start
+    } else if (STOP_CODONS.has(codon)) {
+      const inFrameStart = starts[frame]
+      if (inFrameStart === null) {
+        continue
+      }
+      const length = start - inFrameStart
+      if (!longest || longest[1] - longest[0] < length) {
+        longest = [inFrameStart, start]
+      }
+      starts[frame] = null
+    }
+  }
+  return longest
+}