Sweet yellow tomatoes with a pear shape bring a high price per basket to growers. Pear shape, yellow color, and terminal flower
position are recessive traits produced by alleles, f, r, and t, respectively. The dominant phenotypes for each trait – full shape, red color, and axial flower position – are the product of dominant alleles F, R, and T. A farmer has two pure-breeding tomato lines. One is full, yellow, terminal and the other is pear, red, axial. Design a breeding experiment (crosses) that will produce a line with tomato that is pure-breeding for pear shape, yellow color, and axial flower position.
Answer and Explanation: The farmer has a pure-breeding line of tomato means the farmer has a tomato with genotype FFrrtt while the other line of tomato has genotype ffRRTT.
The cross between these lines gives a F1 generation of heterozygous full, red and axial or FfRrTt.
With an individual of F1 crosses with another individual of F1, the Punnet Square will be:
FfRrTt x FfRrTt
1) Dividing each characteristics, for simplicity:
F f
F FF Ff
f Ff ff
R r
R RR Rr
r Rr rr
T t
T TT Tt
t Tt tt
Analysing Punnett squares, we notice the line wanted (ffrrTT) will be produced, when an individual of F1 generation cross with another individual with the same generation.
