Young Writers Society

I am having some difficulties with some punnet squares, and I'd like some help.

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1. A tall (Tt) red flower (RR) plant is crossed with a tall (Tt) white flower (rr) plant.

Genotype:

Phenotype:

I have to figure out what the genotype and phenotype of the offspring will be, using a punnet square. So, I have to set up a square:
___T____t___R____R
T [TT] [Tt] [TR] [TR]
t [Tt] [tt] [Rt] [Rt]
r [Tr] [tr] [Rr] [Rr]
r [Tr] [tr] [Rr] [Rr]

So, did I fill in that table correctly? I'm pretty sure I did it right.

So, if I did that right, the genotype and phenotype should be as the following:

Genotype: 1 TT; 2 Tt; 4 Tr; 1 tt; 2 TR; 2 Rt; 4 Rr

Phenotype: 9 tall; 3 short; ???

And now I'm confused. So, any help as to how to fill this out, or if I've made any mistakes, please tell me. This stuff is hard for me.

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2. A heterozygous round seed and a heterozygous green seed is crossed with a heterozygous round seed and a heterozygous green seed.

Parent Genotype:

Offspring Genotype:

Offspring Phenotype:

So, a heterozygous round seed (let's say Rr) and a heterozygous green seed (let's say Gg) is crossed with a heterozygous round seed (Rr) and a heterozygous green seed (Gg).

So, we are comparing more than 2 different things here, so how would I make the punnet square? I'm so confused.

Would the parent genotype be:

Parent Genotype: Rr x Gg x Rr x Gg

? Anymore help with these problems would be just fantastic. Thanks for your time!

-Jared

Hey, Jared! ^_^

1.

First of all, let's go back to the beginning. =] If you are going to cross a TtRR plant with a Ttrr plant, we're going to have to find out what kinds of eggs they can make {which would go across the top of the square} and what kinds of sperm they would make. You can actually use the old algebra tool, FOIL here.

The first kind of egg might be TR {first}, then TR {outside}, then tR {inside}, then tR{last}. So really, you only have two types of eggs that can be produced from that first flower.

The sperm would be Tr, Tr, tr, and tr. Again, only really two types.

Now, when you're going to combine these, you'll have to have a gene for both traits on the offspring, right? You can't just code for tall or just code for short, you have to code for height and color.

Then, the resulting punnett square from that would look like this:

_____TR____TR_____tR_____tR
Tr [TTRr]_[TTRr]_[TtRr]_[TtRr]
Tr [TTRr]_[TTRr]_[TtRr]_[TtRr]
tr [TtRr]__[TtRr]__[ttRr]_[ttRr]
tr [TtRr]__[TtRr]__[ttRr]_[ttRr]

I guess since there are only two types of genotypes though, it could also be like this:

_____TR____tR
Tr [TTRr]_[TtRr]
tr [TtRr]__[ttRr]

This would result in the following phenotypes:

Three quarters of the plants would be TALL and RED, because they have the dominant T's and R's, but one quarter of the plants would be SHORT and RED. {that last box}.

2.

Here, you're going to end up having two traits in one thing, just like before, which would result in something like AaBb {A being one trait with two alleles and B being another trait with two alleles}.

Allele = different form of the same gene. ^_^ Just in case.

Anyways, yeah. We'll use the letters you assigned to the traits! {R and G}

You got the genotypes right, but you'd just write it like 'RrGg x RrGg'.

Then you're going to find the eggs and sperm again, which would be like RG, Rg, rG, and rg. Because we have four traits this time, you'll need to use that larger punnett square, but instead of T and R, you'll have R and G and then fill in the correct cross traits.

I hope I helped. C: We just went over this in my bio class.
PM me if you have any questions! ^_^

-Hannah-

_____TR____TR_____tR_____tR
Tr [TTRr]_[TTRr]_[TtRr]_[TtRr]
Tr [TTRr]_[TTRr]_[TtRr]_[TtRr]
tr [TtRr]__[TtRr]__[ttRr]_[ttRr]
tr [TtRr]__[TtRr]__[ttRr]_[ttRr]

I don't get how you came up with this? The way my teacher taught this is to take each single letter from the letters... um... like shown in the diagram below. Can you explain how you came up with this more complicated chart?

-Jared

Well, the thing is that you can't separate the traits, because then you're coding for a tall plant that apparently has no colour, or a colourful plant that lacks height.

The fact that you've got types like I mentioned above means you missed something.

Now, you need to figure out what one flower could make on its own. We're going to start with flower A, TtRR.



'Kay. Now for Flower B, Ttrr.



So now you take the results from A and put them along the top, then the results of B and put those along the left side.



Ta-da! The first two graphs show you the type of genes these flowers could pass on, and in what combinations. When you cross them with the other flower, you get offspring. ^^

Hope I helped!

Teague
x

Thank you, Teague! That makes a lot more sense! I was confused because I didn't get how some tall plants lacked color and some colored plants lacked height. Thanks!

-Jared

Sorry I didn't explain it well enough. Thanks for helping clarify though, Teaguerz. ^_^