In foxes there are three different true-breeding breeds, all of which give rise
ID: 61163 • Letter: I
Question
In foxes there are three different true-breeding breeds, all of which give rise to silver fur color. The normal wilde fox color is tan. A silver breed called pale gives off tan offspring when crossed to another silver breed called shadow. A third silver breed called metal gives tan offspring when crossed to pale but all silver offspring when crossed to shadow.
a. Write the genotypes of all three silver breeds:
b. In a pale x shadow cross, the F2 generation is 9/16 tan and 7/16 silver. In a pale x metal cross, the F2 genereation is all ailver. From this info diagram the biochemical pathway for fur color in foxes.
Explanation / Answer
a) wild color is tan silver breed pale
TT T1T1
TT, TT1, TT1,T1T1 possible offsprings
here TT1=2 T1T1=1 TT=1 phenotypic ratio= 3 tan 1 silver
The offspring tan was crossed with another second silver breed called shadow
TT1 * T2T2
TT2 ,TT2, T1T2,T1T2
here 2 tan 2 silver off springs
the third silver breed is T1T2 is crossed withe pale
TT1*T3T3
TT3,TT3,T1T3,T1T3, all are silver offsprings
two pale and two silver
all silver offsprings crossed with shadow
T1T2*T2T2
T1T2,T1T2,T2T2,T2T2
all are silveroffsprings but genotypic ratio is 2:2
b) When gene products act sequentially, as in a biochemical pathway an allel expressed as a defective enzyme
early in the pathway the same genes that create fur variation might influence other things as well as fur colouring
pigments are produced by the same biochemical pathway as certain brain substances such as dopamine which a
great influence on behaviour. This type of gene interaction in which one gene can interfere with expression of
another is the basis of the phenomenon called epistasis.
In this dominant allels encode functional enzymes and the recessive allells encode nonfunctional
enzymes. In 16 genotypes 9 contain at least one domains allele. remainina 7 genotypes lack dominant alleles.