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Intro genetics problems

Genetics as it applies to evolution, molecular biology, and medical aspects.

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Intro genetics problems

Postby LinuxPoser » Wed Feb 03, 2010 6:07 pm

Snapdragons (Antirrhinum) posses the pigment anthocyanin, which renders petals purple. Two pure anthocyanin-less Antirrhinum lines were developed, one in California and one in Holland. They looked identical in having no pigment at all, manifested as white flowers. However, when petals from the two lines were ground up together in buffer in the same test tube, the solution, which appeared colorless at first, gradually turned purple.
a) What could account for the production of the purple color in the test tube?
b) According to your explanation for part (a), what would be the genotypes for the two lines?
c) If the two white lines were crossed, what would you predict would be the phenotypes of the Fl and F2?


I'm having trouble figuring out how to make this work. I assume there must be an inhibiting enzyme preventing color from being expressed in one line, or else the cross of pure lines would just result in white white. I assume one is a pure line iipp, and the other is IIPP, however it makes the rest of the problem quite complicated. Any input?
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Postby JackBean » Wed Feb 03, 2010 7:44 pm

Hi,
probably, they were mutated in different genes, so when mixed, in the solution were enzymes from both flowers leading to complete pathway.
Try to think about that and what to do with the rest ;)
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Postby jwalin » Thu Feb 04, 2010 2:27 am

there could be 2 things one what jackbean said and another is as follows:
the allele for white is dominant. lets take it to be C and for purple is c. te 2 flowers tat were crushed could be Cc and when mixed you get cc also and then you can get purple color. you will also get the colorless color but that won't be seen

Cc * Cc=.....
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Postby jwalin » Thu Feb 04, 2010 2:33 am

@jackbean i am not very sure of your mechanism now

due to mutation you get a recessive allele. and you would the mutation to take place on both the chromosomes and at the same location, which is nearly impossible, to get the white color. and if they do happen at both places then you never get the purple color.
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Postby jwalin » Thu Feb 04, 2010 2:34 am

and now if you say that the mutated allele is dominant. although i don't know its fisibility but let's take it to be true. but then you would want both the flowers with same genotype and that means you want mutations at the locci on both the plants. very less chance you know. and another thing the conditions will be very different in both the places. and one more thing its like outbreeding and in which you try to avoid the expression of mutated genes.
its just near impossible.

i stress on the "near"

sorry i forgot to put it on one post. habits die hard ;) you know
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Postby JackBean » Thu Feb 04, 2010 7:51 am

1) do not post so many times, first think, than write. Or edit your posts!

2) that's impossible to be the white allele dominant :roll: how could you achieve that?
And even if so (:roll:), that doesn't matter in the tube, there are important only the enzymes, unless you're doing tra-tra in vitro and even if so, you would get CCcc, don't forget!

3) my suggestion: you have some pathway: A -> B -> C -> anthocyanin with respective reactions catalyzed by enzems Z, X and Y
So, in one lab, they got e.g. xx, while the other enzymes were working, in the other lab, they got e.g. yy, while the other enzymes were functional.
So, when you mix it, you get complete functional pathway (you get Z from both plants, X fromthe second plant and Y from the first plant).

This is usuall way, how to recognize, whether is some phenotype done by mutation on one or two loci.
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Postby jwalin » Thu Feb 04, 2010 12:15 pm

@jackbean
i didn't understand the 3
and i think i won't be able to due to my being in the 12th.

and as for the 2.
why can't a white allele be dominant?
you remember the rabbit example. if a few rabbits growing in a region where it snows heavily and snows stay all round the year then the allele for white furcoat will be more dominant than that for the brown furcoat?
i think yes
but it could also be because of the selection pressure but then yet again don't the selection pressure change the allele frequencies and then later also affects the dominance of the allele
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Postby JackBean » Thu Feb 04, 2010 2:31 pm

Do not confuse frequency and dominance of an allele! These has nothing in common (although the dominance is relative).
The allele for white color is probably caused by defective gene resulting in defective protein, which is not able to catalyze its reaction, thus the pathway is blocked and no pigment is produced.
The pathways producing pigments include several steps, for anthocyanins look to wiki or KEGG. Anyway, any of these enzymes can be broken and thus the complete pathway goes to hell, if so, you don't get pigment, you have white whatever, but if you have one corrupted and one functional gene, what will you get? White or color?
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