Tomatoes obtained from hybridization of plants with pear-shaped and globular fruits had only globular fruits.

Tomatoes obtained from hybridization of plants with pear-shaped and globular fruits had only globular fruits. The second generation of tomatoes, grown from seeds extracted from globular fruits, had 1,780 plants with globular fruits and 603 with pear-shaped ones. How should hybridization be carried out so that the offspring have 50% globular fruits and 50% pear-shaped?

Since in F1 all tomatoes had spherical fruits, it should be concluded that the gene that determines this trait was dominant. Let’s designate it as G, then the gene for pear-shaped tomatoes will be g. The parent plants, given the lack of splitting in F1, are pure lines. Let us write globular tomatoes as GG, they will produce germ cells G. Tomatoes with a pear-shaped fruit will be gg, since homozygosity is a condition for the phenotypic realization of this trait. Such tomatoes produce germ cells g. All F1 tomatoes have spherical fruits and genotype Gg. They produce G and g germ cells.

In F2, the appearance of pear-shaped tomatoes (gg) – 25% and ball-shaped tomatoes (GG and Gg) – 75%.

It is necessary to obtain 50% of the pear-shaped tomatoes that have the gg genotype and 50% of the globular-fruit tomatoes. To do this, cross heterozygous globular fruit tomatoes (Gg, G and g gametes) with pear-bearing tomatoes (gg, g gametes). We get offspring: gg – 50%, pear-shaped tomatoes and Gg – 50%, globular tomatoes.

Answer: it is necessary to cross heterozygous globular tomatoes Gg (which are all F1 hybrids) and pear-shaped tomatoes gg.