Week7a+Key+to+selected+questions

Here most if not everyone defined the disorder by the mutation, as if every mutation leads to a disorder and every disorder is caused by a mutation. Both of them are inaccurate. A disorder can occur from new combinations of alleles that already exist. But we didn't talk about that yet. But we did mention that not every mutation leads to a worse situation. And what if the mutation was beneficial? Would its outcome phenotype still considered a disorder?
 * 1. a. When is a certain phenotype called a "disorder"?**
 * b. If we have two alleles for a certain gene, what determines which allele we call "mutant" and which "normal"?**
 * Hint: Tricky question.**

per2MelissaS wrote: "...when a mutation in the DNA happens. or when a gene mutates from one gene to another."

//This correct, if used for the answer of 1b. Mutations are errors that lead to changes in the DNA. They may or may not affect the order of amino acids. Many students wrote that a mutation is defined by the amino acid change, which is incorrect.// So lets put both question together. If mutation can lead to neutral and even beneficial results, how do we decide which allele is normal? ANswer: By what came first, as far as we can tell. In other words, if we have evidence that one allele is more ancient than the other, then 'the other' would be considered the mutant. 'Normal' would be the allele that came first. As for what defines a disorder, it would be the allele that damages us most. And then of course not every trait has a particular value, not everything is 'good' or 'bad'. So a disorder is a condition that is clearly 'bad' to have. But can the 'bad' be the 'normal' one? I say YES. Per6RosaR Wrote: " If a trait "skipped a generation" then the trait is carried by a recessive allele because the parents might have been heterozygote for that trait that means that they were carriers but they did not show it."
 * 2. From the test review guide,**
 * a. Question 21: If a trait ‘__skipped a generation’__ – is the trait carried by the recessive or dominant allele? Explain. **

Rosa correctly begins with the identification of the parents as heterozygotes, which leads her to define them as carriers, who not show the symptoms but pass on the disorder. By definition, this points to the recessive nature of the disorder.