|
First, you'll need to find which gametes each parent can produce. Each gamete needs to contain a "b" and an "r", either in upper or lower case to make a "whole" oraganism - remember that each gamete has to have the "instructions" for everything in the offspring, so you can't have two of the same letter, and none of the other. This is where you use FOIL, using the First of each 'type" of letter, the Outside, the Inside, and the Last. So for your first parent (Bbrr) you'd have
F = Br
O = Br
I = br
L = br
and for the second (bbrr) you'd have
F = br
O = br
I = br
L = br
Since you have four potential gametes from each parent (even though some of the gametes may be exactly the same, as in this example), your Punnett square should be 4 blocks by 4 blocks like this:
....|BR|BR|br|br|
br|
br|
br|
br|
Now, just fill in the square by combining the letters from the top with those of the side into each of the 16 blocks inside the square (do this on a separate piece of paper, using the square as I've made it above). Each block should have 4 letters, 2 of each type. Keep like letters together (as in bbrr, not brbr). If either of a set of letters is uppercase, put that letter first (Bbrr, not bBrr). This will make it easier to find the genotypes and phenotypes later.
The genotypes you can get just by counting how many of each "type" you have. Start at the top left inside the square and go across the top row, then move down to the second row, then the third and fourth. Write down each new genotype as you come to it, then make a hatch mark ( "|" ) to record each block of the square that has that genotype. I'll tell you, there are only two, and they both have the same number for possible offspring with that genotype).
To figure out the phenotypes, refer to the list you made for genotypes and find the phenotype for each genotype you have listed. Remember that if you have either one or two uppercase letters for the same letter (BB or Bb) it is the dominant genotype which is expressed. The only way you can get a recessive phenotype is for both alleles (versions of a gene) to be in the recessive form (bb). You'll already have a count of how many there are in each genotype, so use those numbers for phenotypes. Sometimes, you'll have more than one genotype that results in the same phenotype (for example, BBRR, BbRR, BBRr, and BbRr would all be the same phenotypes for the traits in this problem - don't worry, you don't have all these!). If that happens, just add the numbers for those genotypes together.
To express your numbers as ratios, just put a colon ( ":" ) between the number.
Your genotypic ratio is ____Bbrr : ___bbrr
Your phenotypic ratio is _____ (name of traits) : _____ (name of traits)
|
Quick Reply
