1) Assume independent assortment and start with a plant that is dihybrid A/a ; B
ID: 12653 • Letter: 1
Question
1) Assume independent assortment and start with a plant that is dihybrid A/a ; B/b
a. What phenotypic ratio is produced from selfing it?
b. What genotypic ratio is produced from selfing it?
c. What phenotypic ratio is produced from testcrossing it?
d. What genotypic ratio is produced from testcrossing it?
2. 4) In dogs, dark coat color is dominant over albino and short hair is dominant over long hair. Assume that these effects are caused by two independently assorting genes, and write the genotypes of the parents in each of the crosses shown here:
Use the symbols C and c for the dark and albino coat-color alleles and the symbols S and s for the short-hair and long-hair alleles, respectively. Assume homozygosity unless there is evidence otherwise.
What are the most probable genotypes for the parents in each cross? Write your answers above each parental phenotype in the table above
3) From a presumed testcross A/a × a/a, in which A represents red and a represents white, use the 2 test to find out which of the following possible results would fit the expectations of the presumed testcross (critical value table for the 2 can be found in my lecture slides):
a) 120 red, 100 white
b) 5000 red, 5400white
c) 500 red, 540 white
d) 50 red, 54 white
Explanation / Answer
) Assume independent assortment and start with a plant that is dihybrid A/a ; B/b
a. What phenotypic ratio is produced from selfing it?
Aa Bb x Aa Bb
phenotypic ratio----9:3:3:1
b. What genotypic ratio is produced from selfing it?
genotypic ratio 1:2:2:1:4:2:1:2:!
c. What phenotypic ratio is produced from testcrossing it?
Aa Bb x aa bb
ABa b
Aba b
aBa b
aba b
phenotypic ratio ---------1:1:1:1
d. What genotypic ratio is produced from testcrossing it?
genotypic ratio-----------1:1:1:1
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