{
  "id": "recombination-frequency",
  "version": "921bfbf40d32",
  "status": "published",
  "name": "Recombination Frequency Calculator",
  "question": "What is recombination frequency?",
  "summary": "Finds the recombination frequency between two linked genes from the recombinant and total offspring counts of a cross, with the map distance in centimorgans, or the recombinant offspring to expect from a map distance.",
  "category": "biology",
  "subcategory": "genetics",
  "url": "https://www.acalculator.org/biology/recombination-frequency-calculator",
  "markdown": "https://www.acalculator.org/biology/recombination-frequency-calculator.md",
  "kind": "function",
  "method": "RF = recombinant offspring ÷ total offspring; map distance (cM) = RF × 100; expected recombinants = total offspring × map distance ÷ 100.",
  "assumptions": [
    "The counts come from a cross that shows recombination directly, such as a test cross of a double heterozygote with a double recessive.",
    "One map unit (1 cM) is 1% recombination. This holds for genes close together; frequencies do not go above 50%, so map distances add up only over short spans."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "find": {
        "title": "Find",
        "description": "The recombination frequency from offspring counts, or the recombinants to expect from a map distance.",
        "type": "string",
        "enum": [
          "rf",
          "exp"
        ]
      },
      "r": {
        "title": "Recombinant offspring",
        "description": "Offspring with a new combination of the two traits, summed over both recombinant classes.",
        "type": "integer",
        "minimum": 0,
        "maximum": 1000000000
      },
      "cm": {
        "title": "Map distance (cM)",
        "description": "The distance between the two genes in map units (centimorgans), from 0 to 50.",
        "type": "number",
        "minimum": 0,
        "maximum": 50
      },
      "n": {
        "title": "Total offspring",
        "description": "All offspring counted: parental and recombinant classes together.",
        "type": "integer",
        "minimum": 1,
        "maximum": 1000000000
      }
    }
  },
  "outputs": {
    "result": {
      "label": "Answer",
      "description": "The recombination frequency and map distance, or the recombinant offspring to expect.",
      "format": "text"
    },
    "percent": {
      "label": "Recombination frequency (%)",
      "description": "Recombinant offspring as a percent of all offspring.",
      "format": "number"
    },
    "fraction": {
      "label": "Recombination frequency (fraction)",
      "description": "Recombinant offspring ÷ total offspring, from 0 to 1.",
      "format": "number"
    },
    "cm": {
      "label": "Map distance (cM)",
      "description": "The distance in map units: 1 cM for each 1% recombination.",
      "format": "number"
    },
    "recombinants": {
      "label": "Recombinant offspring",
      "description": "Offspring with a new combination of the traits.",
      "format": "number"
    },
    "parentals": {
      "label": "Parental offspring",
      "description": "Offspring with a parent’s combination: total minus recombinants.",
      "format": "number"
    },
    "perClass": {
      "label": "Each recombinant class",
      "description": "Half the recombinants: the two reciprocal recombinant classes are expected in equal numbers.",
      "format": "number"
    },
    "linkage": {
      "label": "Linkage",
      "description": "Below 50%: linked genes. 50%: independent assortment. Above 50%: check which classes are parental.",
      "format": "text"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "find": "rf",
      "r": 50,
      "cm": 17,
      "n": 1000
    },
    "outputs": {
      "result": "RF = 5% (5 cM)",
      "percent": 5,
      "fraction": 0.05,
      "cm": 5,
      "recombinants": 50,
      "parentals": 950,
      "perClass": 25,
      "linkage": "linked: below 50% recombination"
    },
    "text": "RF = 5% (5 cM) from 1,000 offspring."
  },
  "examples": [
    {
      "given": {
        "find": "rf",
        "r": 50,
        "n": 1000
      },
      "expect": {
        "percent": 5,
        "cm": 5,
        "parentals": 950,
        "result": "RF = 5% (5 cM)",
        "linkage": "linked: below 50% recombination"
      },
      "source": "OpenStax, Biology 2e, §13.1 Chromosomal Theory and Genetic Linkage (recombination frequency = recombinant offspring ÷ total; 0.01 = 1 cM; 0 to 0.5), https://openstax.org/books/biology-2e/pages/13-1-chromosomal-theory-and-genetic-linkage: 50/1000 = 0.05, or 5 percent; Python 3"
    },
    {
      "given": {
        "find": "rf",
        "r": 391,
        "n": 2300
      },
      "expect": {
        "percent": 17,
        "fraction": 0.17,
        "result": "RF = 17% (17 cM)"
      },
      "source": "OpenStax, Biology 2e, §13.1 Chromosomal Theory and Genetic Linkage (recombination frequency = recombinant offspring ÷ total; 0.01 = 1 cM; 0 to 0.5), https://openstax.org/books/biology-2e/pages/13-1-chromosomal-theory-and-genetic-linkage, Morgan’s cross: (206 + 185) ÷ 2,300 = 17 percent; Python 3"
    },
    {
      "given": {
        "find": "exp",
        "cm": 17,
        "n": 2300
      },
      "expect": {
        "recombinants": 391,
        "parentals": 1909,
        "perClass": 195.5,
        "result": "391 recombinant offspring expected"
      },
      "source": "OpenStax, Biology 2e, §13.1 Chromosomal Theory and Genetic Linkage (recombination frequency = recombinant offspring ÷ total; 0.01 = 1 cM; 0 to 0.5), https://openstax.org/books/biology-2e/pages/13-1-chromosomal-theory-and-genetic-linkage, Figure 13.4: 65.5 − 48.5 = 17 cM; hand calculation in content.mdx: 2,300 × 17 ÷ 100 = 391; Python 3"
    },
    {
      "given": {
        "find": "rf",
        "r": 500,
        "n": 1000
      },
      "expect": {
        "percent": 50,
        "linkage": "unlinked: 50% recombination, as for independent assortment"
      },
      "source": "OpenStax, Biology 2e, §13.1 Chromosomal Theory and Genetic Linkage (recombination frequency = recombinant offspring ÷ total; 0.01 = 1 cM; 0 to 0.5), https://openstax.org/books/biology-2e/pages/13-1-chromosomal-theory-and-genetic-linkage: a frequency of 0.5 means the genes behave as unlinked; hand calculation in content.mdx"
    }
  ],
  "sources": [
    "OpenStax, Biology 2e, §13.1 Chromosomal Theory and Genetic Linkage: recombination frequency as the share of recombinant offspring (50/1000 = 0.05), Morgan’s cross (965, 944, 206 and 185 offspring; 17 percent), map units (0.01 = 1 cM), the range from 0 to 0.5, Sturtevant’s map and Figure 13.4 (body color 48.5 cM, wing length 65.5 cM). https://openstax.org/books/biology-2e/pages/13-1-chromosomal-theory-and-genetic-linkage (retrieved 2026-10-19)"
  ],
  "related": [
    "punnett-square",
    "hardy-weinberg",
    "blood-type",
    "baby-eye-color"
  ],
  "changelog": []
}