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punnet squares phenotype

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

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punnet squares phenotype

Postby Jwright » Fri Feb 17, 2006 1:22 am

ok i get the first part of the punnet squares where u put the letters of the hetero or homozygous or colors but i dont get te phenotype and phenotype ratio and i gotta take quizes over this stuff and im failling cause i dont know how to do it so if anyone of yall juniors seniors or anyone who knows how to do it help me plz :oops: :oops: :lol: :lol:
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Postby kiekyon » Fri Feb 17, 2006 1:52 am

the recessive phenotype=recessive homozygous
dominant phenotype=heterozygous+dominant homozygous
the ratio should be number of dominant:number of recessive
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Postby Lynn » Fri Feb 17, 2006 2:52 am

A phenotype is basically the physical appearance of something. The phenotypic ratio is number of dominant phenotype : number of recessive phenotype. For example, eye colour. If 75% of a couple's children have brown eyes, and 25% have blue eyes the ratio would be brown : blue, or 3:1.
You have to do a phenotypic ratio for every possible combination of phenotypes if you are doing more that one physical trait at a time.(For instance eye colour AND hair colour in a larger punnet square.)
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Postby Dr.Stein » Mon Feb 20, 2006 7:19 am

It will be much easier if someone explains her/him with figures ;)
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Postby Jwright » Wed Feb 22, 2006 3:16 am

yea lol cause were doin like round wrinkled dwarf all those different thing like
heterozygous Tall x heterozygous Tall



when i get done with all that i dont know how to get the phenotype of the problem
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Postby Enzyme » Sun Feb 26, 2006 9:17 pm

Jwright, here you have two examples of Punnet's square. I hope you'll understand finally. If you already have some doubts... Ask again ;).
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Postby baby_shark47 » Tue Mar 07, 2006 4:49 am

well first a phenotype is just the physical apperance like for example....1 red bull:3 white bulls:0 pink bulls....

Homozygous means the same like BB or bb....the big B's represent dominance....the little b's are recessive meaning that the Big B's take over the physical trait....

Heterozygous means pretty much two different types such as Bb or Rr.....

uhh....here's a problem that i have from school i hope it helps....


In humans, dark eyes are completely dominant over light eyes. Cross a father with light eyes(heterozygous) with a mother with light eyes....what is the phenotypic ratio? What is genotypic ratio? What is the chance of having a kid with light eyes?

1)figure out what kind of problem you have= complete dominance
2) pick the letters

B=Brown eyes
b=blue eyes

3)Figure out the parent's genotype
Dad=Bb= because he is heterozygous
Mom=bb=light eyes are recessive

4) do the punnett square= B b
b Bb bb
b Bb bb

5)answer questions

a)2 dark(heterozygous): 2 Light
B)2 Bb: 2 bb
C)1/2 or 50 % chance


i hope this helps you
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