dihybrid crosses

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

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dihybrid crosses

Post by tiny » Thu Nov 10, 2005 9:41 pm

i am so stuck, my bio exam is next week and i have no idea how to do a dihybrid cross!

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Inland Taipan
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Post by mith » Thu Nov 10, 2005 10:47 pm

think of it as a multiplication table
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Post by Leesa » Tue Nov 15, 2005 7:53 am

Even I struggled with these, so i'll try to explain.
You start off with your key, and work out what each thing stands foR. Then you work out the multiplication ie ..homozygous brown rabbit x heterozygous black rabbit.

From the figures you get, you work out the gametes ie ..something like FFgG fGFg
You can only give the offspring, half of the genetic material
So you match the first 4 up, ..Fg Gg FG FF
(something like that) remember you can only give 1/2. Then you work out the next set .. Gg Ff FG fG
You put the first gametes up the top of the Punnet Square

FG Gg Fg FF (the first ones) <<
these are meant to be spaced, matching the bottom ones, but it wouldn't let me do it.

Gg GFGg GgGg GFgg GgFF

Ff FFGf FGfg FFfg FFFf

Fg FFGg FGgg FFgg FFFg

fG FfGG fGGg FfGg FfFG

Then you match them up. << As shown above
It's much easier to comprehend if you match the dominant over the reccesive. So if you have a fFgG, in the first bit, to make it easier you can match it like this FfGg ..makes it easier to comprehend.

After doing all that, you work out the genotypes -the numbers occuring written in a fraction, and then ..the phenotypes, the characteristics of it ie Tall and green.

Hope that helps.

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Post by siya » Tue Nov 15, 2005 8:06 am

dihybrid cross involves 2 traits.it is very similar to monohybrid cross.u just have to keep in mind mendel's principle of independent assortment.using checkers square can make it simpler.e.g.suppose u have to cross TTRr and TtRR.thenTTRr will give gametes TR,Tr andTtRR will give TR and tR.the will cross to give TTRR,TtRR,TTRr and TtRr.

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