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Punnet square question?

Hi,
I am a biology student and have a question about my punnet square.
Is my punnet square correct for this 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.

Great question. KEEP STUDYING SCIENCE!!!!
Science is the only hope for the future of America. America has dramatically lost it's scientific talent in recent decades with a precipitous decline since the administration of George W. Bush. We are, perhaps, a 'once great' nation, and because of our increasing scientific illiteracy we lack the imagination to come up with new ideas. We must stop electing 'anti-science' politicians to high office, such as George W. Bush - the worst president in modern American history and a monumental failure.

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