5. 2 brown mice were mated and 12 offspring resulted. 9 of the offspring were brown yet 3 of them were white. How can this be explained? (show all work).
i think i am better understanding this stuff but im not really sure how to set this problem up. please help me!
i think i am better understanding this stuff but im not really sure how to set this problem up. please help me!
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You have brown mice, but they had white offspring? That means that the parents had to have the gene for white, but that it was "hidden" by the brown. The only way to "hide" a gene like that (well, at your level of biology so far!) is to have it be recessive.
That means that the two parent mice had to have a recessive white gene. It wasn't visible for them, because they also had the dominant Brown gene. So make Brown "B" and white "b", and the parents would be Bb and Bb. That means they are brown, because they have a dominant brown gene, but are also carrying a copy for white. They are Heterozygous.
When they have offspring, a baby mouse could get a B from both parents, and be BB. It could get a B from mom and a little b from dad, and be Bb. Or, it could get the little b from mom, and a big B from dad, and be bB. If it got both little b's...it would be bb.
The four combinations would be BB, Bb, bB, and bb. 3 of those four have a B, so they'd be brown. One of those four is bb, so it would be white. So, out of offpspring, an average of 1/4 would be white, and 3/4 would be brown :)
That means that the two parent mice had to have a recessive white gene. It wasn't visible for them, because they also had the dominant Brown gene. So make Brown "B" and white "b", and the parents would be Bb and Bb. That means they are brown, because they have a dominant brown gene, but are also carrying a copy for white. They are Heterozygous.
When they have offspring, a baby mouse could get a B from both parents, and be BB. It could get a B from mom and a little b from dad, and be Bb. Or, it could get the little b from mom, and a big B from dad, and be bB. If it got both little b's...it would be bb.
The four combinations would be BB, Bb, bB, and bb. 3 of those four have a B, so they'd be brown. One of those four is bb, so it would be white. So, out of offpspring, an average of 1/4 would be white, and 3/4 would be brown :)
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The brown mice both had the genotype Bb; that is, they were heterozygous for the Brown gene. So, the Punnett square looks like:
_____B____b___
B___BB___Bb__
b___Bb____bb__←1/4 of the mice were bb = white
_____B____b___
B___BB___Bb__
b___Bb____bb__←1/4 of the mice were bb = white