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phenotype and genotype ratio

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

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phenotype and genotype ratio

Postby Erised » Sun Dec 11, 2005 1:30 am

Hey everyone. I need help from you again :D

I'm confused about phenotype and genotype ratio after you do a monohybrid cross.

for example, after the cross, I have RR Rr Rr rr, the genotype is 1:2:1 and the phenotype is 3:1, right?

but what if I have Rr Rr rr rr? Is the phenotype 2:2 and genotype 1:1?

what about Rr Rr Rr Rr?

My book doens't explain it very well, please help me guys!
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Postby GreenDog » Sun Dec 11, 2005 8:01 am

2:2 is the same as 1:1, just divide in two.
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Postby MrMistery » Sun Dec 11, 2005 6:49 pm

Geotype means what genes are present: Rr is different from RR, which is different from rr. There are 3 cases. So in a case of Rr Rr rr rr the ratio would be 2:2=1:1. In a case of RR Rr Rr rr the ratio will be 1:2:1, because there are 3 present genotypes.
Phenotype means what genes are expressed. As you know, dominant alleles express over recessive ones, so you will only have 2 possibilities: dominant(RR or Rr) and recessive(rr). In a situation like Rr Rr rr rr the ratio is 1 dominant for every one recessive(1:1). The phenotypical ratio is the same for, let's say RR Rr rr rr(1:1) since in Rr the dominant allele expresses

However, remember, in a monohibridation cross you get 1:2:1 genotype and 3:1 phenotype., according to Mendel. The other ones are made up...
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Postby faliureinbiology » Sun Jan 08, 2006 7:40 pm

Ok,

I am not so good at biology and the teacher and I dont get along so great, so that doesn't help. I have a 7 page homework assignment that I'm deffintly not going to finish..Here's an example of a question... In mice, long ears is dominant to short ears. What are the genotypic and phenotypic ratios id you cross a homozygous long eared mouse with a short eared mouse? so yeah..can anyone help me?! pleaaaase... if so like send me a pm or something and I'll hopefully get this done!
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Postby bearhug » Sun Jan 08, 2006 8:42 pm

AA x aa gives you Aa Aa Aa Aa. All are heterzygous and all are long eared.
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RATIOS?

Postby GENOWHAT » Fri Nov 16, 2007 1:06 am

i dont understand what the ratio is if its Rr Rr Rr Rr

or Rr Rr rr rr PLEASE HELLPPP
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Re: RATIOS?

Postby Ultrashogun » Mon Nov 26, 2007 9:04 pm

GENOWHAT wrote:i dont understand what the ratio is if its Rr Rr Rr Rr

or Rr Rr rr rr PLEASE HELLPPP


Theres no ratio. The situation which you describe is sometimes called Mendels law of uniformity because all the progeny show the phenotype of the dominant allele, so it can be a tool to find out which allele is dominant.

A progeny with Rr Rr rr rr can only be obtained by crossing Rr with rr. A so called "test cross" with the F1 generation. It means crossing with the homozigos recessive to clearly see which kind of gamets it produces.

We have two genotypes with ratio 1:1 and we have two phenotypes with ratio 1:1.
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Re: phenotype and genotype ratio

Postby niasdream90 » Wed Oct 01, 2008 7:53 pm

what is the genotype and phenotype ratio for Ll Ll Ll Ll or Ll Ll ll ll
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Postby canalon » Wed Oct 01, 2008 8:10 pm

read above. Replace R by L and r by l.
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Postby ih8bio » Wed Dec 01, 2010 4:50 am

Im new and i really need help with this Question.
In squash, the allele for white fruits (W) is dominant over the allele for yellow(w). If a white fruited plant is crossed with a yellow fruited plant and all the offspring are yellow, what are the possible genotypes of the parent and the offspring?

a).parents:
b).offspring:
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Postby canalon » Wed Dec 01, 2010 5:01 am

Punnet squares are your friend
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Re: phenotype and genotype ratio

Postby Trevorwin » Thu Sep 15, 2011 7:45 am

The allele for white fruit is W and that of yellow is w. If the cross between white fruit and yellow fruit results in only yellow offsprings, then a test cross must be performed.
Let us cross a homozygous white (WW) with a homozygous yellow (ww). We obtain the following genotypes - Ww and Ww. Since white is dominant over yellow, Ww will result in white fruited plant.
Again, if we cross a heterozygous white (Ww) with a homozygous yellow (ww), we get the following genotypes - Ww and ww, i.e., white and yellow fruited in equal ratios.
Therefore, on crossing a white fruited squash with a yellow fruited squash where white is dominant over yellow, the offsprings produced are either all white or a mixture of white and yellow in equal ratios.
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