You perform a testcross on a tall pea plant. Half the offspring are short. What conclusion can you draw from this outcome?
1 Answer
Tall pea plant in question is heterozygous tall (Tt)
Explanation:
A test cross is performed on a tall pea plant to determine its genotype. There are two possibilities, i.e. it can be either homozygous tall (TT) or heterozygous tall (Tt).
In a test cross, tall pea plant of unknown genotype is crossed with dwarf pea plant. Dwarf plant is always homozygous (tt) as tallness is dominant allele and the dwarfness is recessive allele in pea. It produces gametes with 't' allele only.
All the gametes produced by tall plant will be only of one type carrying 'T' allele if it is homozygous tall (TT). and thus all the offsprings will be tall (Tt).
The gametes containing allele 'T' and 't' will be in the ratio of 1;1 if the given tall plant is heterozygous. Half the offsprings will be heterozygous tall (tt) and half will be dwarf or short (tt) as both tpes of gametes produced will have equal chance to fuse with gametes produced by dwarf plant containing 't'allele.
It is thus concluded from the test cross in question that given pea plant is heterozygous tall as half the offsprings are dwarf (short)
