Teacher Version

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Mystery Trait - Scales and Plates Activity:  Discovering  the inheritance patterns of hidden genes through inductive reasoning.

GenScope File:  ScaledDragon.gs, PlatedDragon.gs

(These files were created using the species builder application. The gene does not show up on the chromosomes for either trait. The dragon, Shaiyda, is homozygous dominant for scales. It is an autosomal trait carried on the first chromosome. Carl has little plates, Pp.The trait, plates, is incompletely dominant and x-linked. Big plates, PP and no plates, pp are the other two possibilities.)

Open the Scaled Dragon file and you will see a dragon that you may not have ever seen before. It has scales all over its body! What's going on here??? Here are some questions for you to work on as you think about this problem.

1.       Is this new trait genetic? In other words, did the scaled dragon inherit scales from its parents? Circle one answer and then explain why you think so.

Yes      No
How can you tell? Explain why you think so.

The answer here is yes.

Since ony the female dragon is given, the student will have to create a male dragon, which will be normal, no scales. When mated both phenotypes are found among the offspring. If the trait wasnít inherited, then none of the dragon babies would have scales.

2.      If it is genetic, how are scales inherited? Is it a dominant condition (like horns), a recessive condition (like wings), and incompletely dominant condition (like legs) or something else? How can you tell?

The trait is a dominant condition, like horns.

When Shaiyda is mated with a male without scales, the resulting baby dragons are mixed-about 1/2 and 1/2 with and without scales. Shaiyda must be Ss and the scaleless male ss if having the trait is dominant. If Shaiyda were SS, then all of the kids would be scaled. If the trait were recessive, then mating two dragons with scales would result in all scaled babies. What actually results is a mixture of scaled and scaleless in an approximate ratio of 1 scaleless for every 3 scaled. If the trait were incompletely dominant, then three different traits would appear-possible scaled, unscaled and partially scaled. This does not occur.

3.       Is the gene for scales sex-linked?  Put a check mark next to one choice only. ___ Sex-linked (on the X or Y chromosome)?
___ Autosomal (on the number 1 or number 2 chromosome)?

How can you tell?

The gene is autosomal on chromosome number 1.

If the gene were x-linked, then all of the male offspring would be scaled and none of the females would have scales. The reason for this is, of course, that the females get their X chromosome from their father, who does not have scales. On the other hand, the males get one X chromosome from each of their parents, and since having scales is dominant, all of the males would have scales.

Open the file Plated Dragon and you will see another different kind of dragon. This one has plates on its neck. Now try to figure out information about this trait. Here are the same questions as before (but some of the answers are different!)

4.       Is this new trait genetic? In other words, did the plated dragon inherit plates from its parents?

Yes      No

How can you tell?

The trait is genetic because some of the offspring inherit the trait.

If the trait were not genetic, then none of the children would inherit the trait. More to the point, and harder for a student to recognize, females can never have small plates! Because small plates is Pp, with an allele on both X chromosomes, only males can have that trait. Only males have two X chromosomes in dragons. Females have one X chromosome and one Y chromosome (indicated by a "-" , which indicates that there arenít any alleles on it.) and so can only have one allele for plates, thus only a P or a p. Because of this females either have big plates or no plates.

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