Punnet square question?

Okay - to take this on we need to understand the genotypes corresponding with the phenotypes you have presented.

For the black sheep the phenotype is easy - it can only be 'aa'. This is because the 'a' allele for black wool is recessive to white and thus, the only option is to be homozygous to have a black wool phenotype.

The ram you mention is white. Since you describe this trait as dominant the genotypes for a white ram can either be homozygous "AA" or heterozygous "Aa".

Thus - there are two possible genotype blends corresponding to the phenotypes you laid out:

Scenario 1:

Homozygous white ram 'AA' crosses with homozygyous black sheep 'aa'.

In this scenario ALL the offspring will be white. See the punnet square below:

A A

a aA aA

a Aa Aa

All the offspring are heterozygous for each allele (a dominant white allele from the ram and a recessive black allele from the sheep). But since 'a' or black wool is recessive all will be white.

Thus Genotype ratio in scenario #1 is 4 heterozygous Aa and 4 white offspring.

Now in scenario #2 the possibility exists that the white ram is in fact heterozygous "Aa" So the punnet square now has different ratios and outcomes. Remember, the black sheep is still by necessity homozygous. See below:

A a

a aA aa

a Aa aa

As you can see, there are two heterozygous white offspring and two homozygous black sheep.

Thus the genotype ratio is 2Aa:2aa.

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First of all, use A for the white wool allele and a for the black to keep with standard conventions. Keep in mind that your ram could be Aa or AA. You will therefore need to generate two Punnett squares. The square you linked to does not show the mating described above; rather, it shows the mating of two heterozygous white animals.

I'm not going to give you the answer - but hopefully you'll get it by thinking about what's wrong with what you have done so far.

Yes the Punnet square is correct, meaning the ratio is 3:1 will be white

That is a heterozygous cross and correct. 3:1

Now, can you do the homozygous cross?

i can't be cure because you don't say wether it is a homogunis white of heterozygous white. so it would be A? * aa which would be Aa a? Aa and a? so you can't tell

Your punett square is correct

r u there what was your question?