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A trait is a characteristic shown by an organism.

For example a Tt plant would show the 'tallness' trait.

It seems to me that, by analogy, sickle cell anaemia (SCA) carriers should show the 'normal' trait, but I have found on various sites that SCA carriers are described as having the sickle cell trait because as carriers they can pass the mutated gene to their children.

This doesn't make sense to me, as showing a trait and passing it to the next generation are two different things. We do not say a Tt plant has the dwarfness trait just because it can pass it to the next generation.

So what is the exact definition of the term 'trait'?

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  • $\begingroup$ Trait is used to mean alleles multiple times, no? $\endgroup$
    – Aurelius
    Oct 14, 2023 at 18:28
  • $\begingroup$ I think you are interested in the difference between phenotype and genotype. $\endgroup$ Oct 18, 2023 at 22:09
  • $\begingroup$ @David is there any official book for biological definitions just like we have IUPAC goldbook for definitions of chemistry? $\endgroup$ Dec 26, 2023 at 10:21
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    $\begingroup$ @HarjotDhillon — In a word, no. Biochemists and Molecular Biologists have a joint Nomenclature Commission with IUPAC, which is available on a 20th century website the design of which is unbelievably awful. There are various specialist bodies for taxonomical nomenclature in various fields, but you won't find terms like 'trait' defined anywhere but textbooks. At least not to my knowledge. It's a bit of a moving target anyway, and convention emerges from the usage of the 'leaders' in the fields, without anyone trying to codify it. $\endgroup$
    – David
    Dec 27, 2023 at 11:04

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I think the confusion stems from the word "trait" being used differently on the website you link, from how we use it in genetics. From the website:

A trait is something unique about you, like your hair or eye color. Traits are passed down (inherited) from your parents. Genes carry information that makes a trait. People with sickle cell trait (SCT) have 1 sickle cell gene and 1 normal gene. Having sickle cell trait is not the same as having sickle cell disease (SCD). Sickle cell trait means you could pass sickle cell trait or disease to your children.

Thus, we see SCT, Sickle Cell Trait, is a specific condition someone can have, just like they could have SCD, sickle cell disease, or nothing at all.

I don't think the use of the word "trait" has much to do with how we use it in biology. You are right that in biology, we usually use the word "trait" interchangeably with the word "phenotype" whereas in the website you link, it explains "Sickle Cell Trait" is the name of a heterozygous genotype for sickle cell.

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