Question 29

[zeina_ghou6141]

For question #29, if the change would make trait B recessive, why would all of the offspring have trait B? Wouldn't that be the case if B was dominant? Thanks for your help!

[admin]

Not exactly.

If trait B was dominant, then yes, it would be true that BB x BB would give you all offspring that our BB and thus have the disease. However, if you had Bb x Bb, both parents would still have the disease but there would be a 25% probability of having offspring without the disease.

But if Trait b is recessive, the only way the parents could each have the disease is if they are both bb. And thus bb x bb only makes offspring that are bb: thus all have the disease.

[yfangl097543]

I don't see how the change makes trait B recessive...

[admin]

13 expresses trait B (according to Figure 1). However, the parents of 13 (8 and 9) do NOT express trait B (8 is now a solid line organism and 9 always expressed trait A). So here becomes the question: how is it that 1/3 offspring from parents 8 and 9 express trait B but neither 8 nor 9 express trait B? Well, trait B must have been recessive and 8, 9 were carriers of the recessive gene.

[admin]

bump

[hua8986059]

damn this passage was SOOOO time consuming i mean I could figure everything out but it feels like my brain is going 18000000 mph while solving these lol...