Genetics? Dealing with phenotype/genotype?

Question

In pigs, assume white coat color (W) is dominant to black (w). If two white pigs are mated & produce 12 white & 5 black offspring, what proportion of the white offspring are probably homozygous for this color? Thanks, 10 pts to best answer

Answer 1

First you should note that since there are black offspring both white parents must be heterozygotes (otherwise all of the offspring would be white).  Now with this knowledge in hand you can solve the problem using a Punnett square (minus the square since I can't get it to look right on here :).

____W____w

W__WW      Ww

w __Ww       ww

Note: Parent 1 is across the top & parent 2 is along the left side.

From the square you learn that 1/4 of the offspring will have the genotype WW (white phenotype), 1/2 will have the genotype Ww (white phenotype) and 1/4 will have the genotype ww (black phenotype). So given that there are 17 offspring we can calculate the probable number of homozygous white pigs by multiplying.

17 * 1/4 = 4.25

Therefore the answer is approximately 4.

Answer 2

Well first you should make a punnent square

W*W * w - sorry, bad square, hopefully you know how to make

*

w



so 1/4 of the pigs are probably homozygous dominant, so 17/4 = about 4

Answer 3

the punnet square has to be with two pigs that are Ww, so it would look like this:

     W * w

W

*

w

you will then get that 75% of the F1 will be white. so out of the white offsprings you have 33% (or 1/3) that they are homozygous and 66% (or 2/3) that they are heterozygous. 33% (or 1/3) out of 12 is 4.