--- title: "Blood Type Inheritance | Anatomy and Physiology I" description: "Blood type inheritance is the passing of ABO and Rh alleles from parents to child, shaping blood antigens and transfusion compatibility in A&P I." canonical: "https://fiveable.me/anatomy-physiology/key-terms/blood-type-inheritance" type: "key-term" subject: "Anatomy and Physiology I" unit: "Unit 18" --- # Blood Type Inheritance | Anatomy and Physiology I ## Definition Blood type inheritance is the way ABO and Rh alleles from your parents determine the antigens on your red blood cells. In Anatomy and Physiology I, it shows how genotype predicts blood type and transfusion compatibility. ## What It Is Blood type inheritance in Anatomy and Physiology I is the passing of ABO and Rh alleles from parent to child, which determines which antigens appear on red blood cells. Those antigens are what blood typing labs look for when they label someone as A, B, AB, or O, and Rh positive or Rh negative. The ABO system follows codominance. That means the A allele and B allele can both be expressed at the same time, so a person with genotype AB makes both A antigen and B antigen. The O allele does not make either antigen, so OO gives type O blood. A and B each act as dominant over O, but A and B are codominant with each other. In many A&P problems, you will see these as IA and IB alleles, but the idea is the same. The Rh system works a little differently. The Rh factor usually refers to the D antigen, and having at least one D allele makes a person Rh positive. If someone inherits two recessive alleles and does not make the D antigen, they are Rh negative. So when you work with blood type inheritance, you are often tracking two inherited traits at once, ABO and Rh. A parent passes one allele for ABO and one allele for Rh to each child. That is why two type A parents can have a child with type O if both carry the O allele, and why Rh positive parents can still have an Rh negative child if both carry the recessive allele. Punnett squares are the usual tool for sorting these outcomes, because they show possible genotype combinations before you translate them into blood type. This topic also connects to blood bank compatibility. Your inherited antigens are not just labels, they affect whether plasma antibodies will attack donated red blood cells. If donor antigens do not match the recipient’s antibodies, the immune system can trigger agglutination and hemolysis. In A&P, that makes blood type inheritance a genetics topic with a very real body-level consequence. ## Why It Matters Blood type inheritance shows how genetics turns into a physiology problem. Once you know which antigens are on red blood cells, you can predict whether a transfusion is safe, whether a recipient already has antibodies against donor cells, and why certain blood types are more flexible donors than others. It also gives you a clean example of codominance and recessive inheritance in the same system. ABO is a classic codominance case, while Rh is a simpler dominant and recessive pattern. That mix shows up often in A&P quizzes because it tests whether you can move from genotype to phenotype without mixing up the two systems. This term also matters for pregnancy and newborn health. If an Rh negative mother carries an Rh positive fetus, her body can become sensitized and later make antibodies that attack fetal red blood cells. That is the pathway behind hemolytic disease of the newborn, and it is why Rh status gets checked so carefully in prenatal care. In lab or case questions, blood type inheritance is one of the easiest places to practice reading from genotype to phenotype to medical outcome. If you can trace the alleles, you can explain why a mismatch is dangerous and why blood banking has to be exact. ## Connections ### Alleles Blood type inheritance starts with alleles because each parent gives one version of the ABO gene and one version of the Rh gene. In A&P, the point is not just naming the alleles, but using them to predict which antigens end up on red blood cells. That is the bridge from genetics to blood typing. ### Codominance The ABO system is one of the clearest examples of codominance. If a person inherits A and B alleles, both antigens show up, so the phenotype is AB rather than one trait hiding the other. That makes ABO different from the simpler dominant recessive patterns you may see in other inheritance problems. ### [Rh blood group](/anatomy-physiology/key-terms/rh-blood-group) Blood type inheritance often includes the Rh blood group, which tells you whether the D antigen is present on red blood cells. This system matters because Rh positive and Rh negative status changes transfusion matching and pregnancy risk. It is usually taught right alongside ABO because you need both to describe a full blood type. ### [hemolytic disease of the newborn (HDN)](/anatomy-physiology/key-terms/hemolytic-disease-of-the-newborn-hdn) Rh inheritance helps explain hemolytic disease of the newborn. If an Rh negative mother is exposed to Rh positive fetal blood, she may make antibodies that cross the placenta in a later pregnancy. Those antibodies can destroy fetal red blood cells, which is why this condition shows up in A&P blood typing units. ## On the AP Exam A quiz question might give you the parents’ blood types and ask for possible child blood types, so you would use genotype logic, not just phenotype labels. If both parents are type A, for example, you check whether they could each carry an O allele before deciding whether a type O child is possible. For Rh questions, you track the D antigen separately and look for dominant Rh positive versus recessive Rh negative inheritance. You may also see blood typing in lab-based questions where you identify antigens from an agglutination pattern. In those cases, the job is to read which antibodies clump the sample and then connect that to the inherited antigen on the red blood cell membrane. If the question includes pregnancy or transfusion, blood type inheritance becomes a safety issue, not just a genetics one. ## Blood Type Inheritance vs blood typing Blood type inheritance is the genetic transmission of ABO and Rh alleles from parents to child. Blood typing is the lab process of identifying which antigens are already present on a person's red blood cells. In other words, inheritance explains how the blood type is passed down, while typing tells you the blood type you have. ## Key Takeaways - Blood type inheritance is the passing of ABO and Rh alleles that determine the antigens on red blood cells. - ABO shows codominance, so A and B can both be expressed in the same person, while O makes no A or B antigen. - Rh status usually depends on the D antigen, and having one dominant D allele makes a person Rh positive. - You can use Punnett squares to predict possible child blood types from the parents’ genotypes. - The big physiology payoff is compatibility, because mismatched blood can trigger agglutination and hemolysis. ## FAQs ### What is blood type inheritance in Anatomy and Physiology I? Blood type inheritance is the way ABO and Rh alleles from your parents determine the antigens on your red blood cells. In Anatomy and Physiology I, it shows up as a genetics-to-physiology topic because the inherited antigens control blood typing, transfusion matching, and Rh-related pregnancy issues. ### How does ABO blood type inheritance work? ABO inheritance uses three main alleles, A, B, and O. A and B are codominant, so together they produce AB blood, while O is recessive and only appears when a person inherits two O alleles. That is why genotype matters more than just the visible blood type label. ### How is Rh inheritance different from ABO inheritance? Rh inheritance usually focuses on the D antigen. One dominant D allele makes a person Rh positive, while two recessive alleles make them Rh negative. Unlike ABO, there are not two codominant antigens here, so the pattern is simpler but still medically important. ### Can two type A parents have a type O child? Yes, if both parents are heterozygous and carry an O allele. A phenotype of type A does not tell you whether the genotype is AA or AO, so two type A parents can sometimes pass O alleles to the same child. That is a common Punnett square question in A&P. ## Related Study Guides - [18.6 Blood Typing ](/anatomy-physiology/unit-18/6-blood-typing/study-guide/vso6m0jhFxV8mBRb) ## About This Document Canonical Fiveable pages are available as Markdown at the same path plus `.md`. - [llms.txt](https://fiveable.me/llms.txt): index of Fiveable's sections and URL patterns - [llms-full.txt](https://fiveable.me/llms-full.txt): complete subject and unit listing - [MCP server](https://fiveable.me/mcp): call Fiveable as tools instead of fetching pages (`https://fiveable.me/api/mcp`) - [MCP server for AP teachers](https://fiveable.me/mcp/teachers): a teacher's classes, assignments and AP-rubric grading (`https://fiveable.me/api/mcp/teacher`) ## Structured Data ```json {"@context":"https://schema.org","@graph":[{"@type":"LearningResource","@id":"https://fiveable.me/anatomy-physiology/key-terms/blood-type-inheritance#resource","name":"Blood Type Inheritance | Anatomy and Physiology I","url":"https://fiveable.me/anatomy-physiology/key-terms/blood-type-inheritance","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/anatomy-physiology/key-terms/blood-type-inheritance#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-07-03T02:20:36.800Z","isPartOf":{"@type":"Collection","name":"Anatomy and Physiology I Key Terms","url":"https://fiveable.me/anatomy-physiology/key-terms"},"author":{"@type":"Organization","@id":"https://fiveable.me/editorial#content-team","name":"Fiveable Content Team","url":"https://fiveable.me/editorial","parentOrganization":{"@id":"https://fiveable.me/#organization"},"member":[{"@type":"Person","name":"Amanda DoAmaral","sameAs":["https://www.linkedin.com/in/adoamaral"]},{"@type":"Person","name":"Becky Bahr","sameAs":["https://www.linkedin.com/in/becky-bahr-b52743132"]}]},"publisher":{"@type":"Organization","name":"Fiveable","url":"https://fiveable.me"}},{"@type":"DefinedTerm","@id":"https://fiveable.me/anatomy-physiology/key-terms/blood-type-inheritance#term","name":"Blood Type Inheritance","description":"Blood type inheritance is the way ABO and Rh alleles from your parents determine the antigens on your red blood cells. In Anatomy and Physiology I, it shows how genotype predicts blood type and transfusion compatibility.","url":"https://fiveable.me/anatomy-physiology/key-terms/blood-type-inheritance","inDefinedTermSet":{"@type":"DefinedTermSet","name":"Anatomy and Physiology I Key Terms","url":"https://fiveable.me/anatomy-physiology/key-terms"}},{"@type":"FAQPage","mainEntity":[{"@type":"Question","name":"What is blood type inheritance in Anatomy and Physiology I?","acceptedAnswer":{"@type":"Answer","text":"Blood type inheritance is the way ABO and Rh alleles from your parents determine the antigens on your red blood cells. In Anatomy and Physiology I, it shows up as a genetics-to-physiology topic because the inherited antigens control blood typing, transfusion matching, and Rh-related pregnancy issues."}},{"@type":"Question","name":"How does ABO blood type inheritance work?","acceptedAnswer":{"@type":"Answer","text":"ABO inheritance uses three main alleles, A, B, and O. A and B are codominant, so together they produce AB blood, while O is recessive and only appears when a person inherits two O alleles. That is why genotype matters more than just the visible blood type label."}},{"@type":"Question","name":"How is Rh inheritance different from ABO inheritance?","acceptedAnswer":{"@type":"Answer","text":"Rh inheritance usually focuses on the D antigen. One dominant D allele makes a person Rh positive, while two recessive alleles make them Rh negative. Unlike ABO, there are not two codominant antigens here, so the pattern is simpler but still medically important."}},{"@type":"Question","name":"Can two type A parents have a type O child?","acceptedAnswer":{"@type":"Answer","text":"Yes, if both parents are heterozygous and carry an O allele. A phenotype of type A does not tell you whether the genotype is AA or AO, so two type A parents can sometimes pass O alleles to the same child. That is a common Punnett square question in A&P."}}]},{"@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Anatomy and Physiology I","item":"https://fiveable.me/anatomy-physiology"},{"@type":"ListItem","position":2,"name":"Key Terms","item":"https://fiveable.me/anatomy-physiology/key-terms"},{"@type":"ListItem","position":3,"name":"Unit 18","item":"https://fiveable.me/anatomy-physiology/unit-18"},{"@type":"ListItem","position":4,"name":"Blood Type Inheritance"}]}]} ```