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Mendelian traits in humans

Mendelian traits in humans is a biology topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Mendelian traits in humans rather than just read about it. In short: Mendelian traits in humans are human traits that are substantially influenced by Mendelian inheritance. Most – if not all – Mendelian traits are also influenced by other genes, the environment, immune responses, and chance.

Mendelian traits in humans — main illustration
Mendelian traits in humans — illustration

Key takeaways

  • Mendelian traits in humans belongs to biology; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Mendelian traits in humans to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Mendelian traits in humans from memory before moving on to harder problems.

Reference excerpt

Mendelian traits in humans are human traits that are substantially influenced by Mendelian inheritance. Most – if not all – Mendelian traits are also influenced by other genes, the environment, immune responses, and chance. Therefore no trait is purely Mendelian, but many traits are almost entirely Mendelian, including canonical examples, such as those listed below. Purely Mendelian traits are a minority of all traits, since most phenotypic traits exhibit incomplete dominance, codominance, and contributions from many genes. If a trait is genetically influenced, but not well characterized by Mendelian inheritance, it is non-Mendelian.

Examples Albinism (recessive) Achondroplasia Alkaptonuria Ataxia telangiectasia Brachydactyly (shortness of fingers and toes) Cataracts Colour blindness (monochromatism, dichromatism, anomalous trichromatism, tritanopia, deuteranopia, protanopia) Duchenne muscular dystrophy Ectrodactyly Ehlers–Danlos syndrome Fabry disease Galactosemia Gaucher's disease Haemophilia Hereditary breast–ovarian cancer syndrome Hereditary nonpolyposis colorectal cancer HFE hereditary haemochromatosis Huntington's disease Hypercholesterolemia Krabbe disease Lactase persistence (dominant) Leber's hereditary optic neuropathy Lesch–Nyhan syndrome Marfan syndrome Niemann–Pick disease Phenylketonuria Porphyria Retinoblastoma Sickle-cell disease Sanfilippo syndrome Tay–Sachs disease Wet (dominant) or dry (recessive) earwax

Non-Mendelian traits Most traits (including all complex traits) are non-Mendelian. Some traits commonly thought of as Mendelian are not, including:

Eye Color Psychiatric diseases Hair color Height Tongue rolling

References

Further reading

External links OMIM Online Mendelian Inheritance in Man Myths of Human Genetics

Illustrations

Mendelian traits in humans: Autosomal dominant
Autosomal dominant
Mendelian traits in humans: A 50/50 chance of inheritance.
A 50/50 chance of inheritance.
Mendelian traits in humans: Sickle-cell disease is inherited in the autosomal recessive pattern. When both parents have sickle-cell trait (carrier), a child has a 25% chance of sickle-cell disease (red icon), 25% do not carry any sickle-cell alleles (blue icon), and 50% have the heterozygous (carrier) condition.[1]
Sickle-cell disease is inherited in the autosomal recessive pattern. When both parents have sickle-cell trait (carrier), a child has a 25% chance of sickle-cell disease (red icon), 25% do not carry any sickle-cell alleles (blue icon), and 50% have the heterozygous (carrier) condition.[1]
Mendelian traits in humans: If one parent has sickle-cell anaemia and the other has sickle-cell trait, then the child has a 50% chance of having sickle-cell disease and a 50% chance of having sickle-cell trait.[1]
If one parent has sickle-cell anaemia and the other has sickle-cell trait, then the child has a 50% chance of having sickle-cell disease and a 50% chance of having sickle-cell trait.[1]
Mendelian traits in humans: An example of the codominant inheritance of some of the four blood groups.
An example of the codominant inheritance of some of the four blood groups.

Worked examples

Example 1 — a first encounter with Mendelian traits in humans

Start with the simplest possible case. Write down what Mendelian traits in humans claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In biology, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Mendelian traits in humans before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Mendelian traits in humans ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Mendelian traits in humans

In research
Mendelian traits in humans appears in biology research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Mendelian traits in humans in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Mendelian traits in humans is common in secondary-school and first-year university syllabi. It links to neighbouring topics Human genetics, so understanding it makes those chapters shorter.
In everyday life
Look for Mendelian traits in humans outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.
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How to study Mendelian traits in humans in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Mendelian traits in humans means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Mendelian traits in humans out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Mendelian traits in humans in simple terms?

Mendelian traits in humans are human traits that are substantially influenced by Mendelian inheritance. Most – if not all – Mendelian traits are also influenced by other genes, the environment, immune responses, and chance.

Why does Mendelian traits in humans matter?

Because it connects several biology ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Mendelian traits in humans?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Mendelian traits in humans.

Tags

  • Human genetics

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