Join TSR now and get all your revision questions answeredSign up now

I dont understand a question

    • Thread Starter
    Offline

    1
    ReputationRep:
    Name:  image.jpg
Views: 35
Size:  502.1 KBThe question says a homozygous red flowered plant was crossed with a homzygous white flowered plant. All the flowers of the offspring were purple. What was the gentoype of the red flowered parent? I put AB and then the next question asks whats the genotype of the white flowered parent? I put aa but I dont think their right is codominance involved.

    Then another question says: The purple flowered offspring were crossed. What phenotypic ratio would you expect in the next generation. Use a genetic diagram to explain your answer.
    I think codominance is involved so I tried to put that in the diagram but it doesnt look right so I'm not sure and someone help me please.
    Attached Images
        
    • Thread Starter
    Offline

    1
    ReputationRep:
    Oops sorry about the so many attachments it didnt show up before so I did it a bunch of times but it still didnt show up then I just typed up the question but now it shows up once I sent it.
    Offline

    3
    ReputationRep:
    So the key thing you've missed here is that it says the different genes are on different chromosomes, so the genotype for each plant is going to need 2 pairs of letters, so the red flower will have the genotype AA bb and the white flower will have aa BB (remember that the B allele only works on the red pigment, so the flower will still be colourless because there is no A allele). A purple flower will then need to have either a Aa Bb or AA BB genotype. So you need to draw a couple of punnet squares, the first one will be AA crossing with aa, which gives you 100% Aa genotype in the offspring, and the second cross will be bb crossing with BB, which gives you a 100% Bb genotype. So the purple flowers all have the genotype Aa Bb, if you cross them with eachother, you will cross Aa with Aa which gives 25% AA, 50% Aa and 25% aa, and then Bb with Bb will again give 25% BB, 50% Bb and 25% bb, so you would have thought that 75% of the offspring are purple and 25% are white.

    That's probably not right actually haha, maybe someone else can correct me if I'm wrong
    • Thread Starter
    Offline

    1
    ReputationRep:
    Thank you
 
 
 
Poll
Do you have exam superstitions?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Quick reply
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.