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 many F2 plants with globular fruits out of 1780 were heterozygous?

Since the first generation of tomatoes had exclusively spherical fruits, it should be concluded that this form is the result of the expression of a dominant gene. Let’s designate it as G, then the pear-shaped form will be due to the g gene, which is homozygous gg.

The parental tomato plants, which had a globular shape, were GG, since there was no splitting in F1 for this trait. These tomatoes produced G.

The gg pear-shaped tomatoes produced g. Thus, all F1 tomatoes were Gg and were globular. They produced G and g germ cells.

In F2, obtained by crossing such tomatoes with each other, the following options were obtained:

tomatoes with spherical fruits (GG – 25% and Gg – 50%) – 75%;

pear-shaped tomatoes (gg) – 25%.

Heterozygous Gg tomatoes accounted for 50% of the resulting plants, or 1780 * 0.5 = 890 plants.

Answer: 890.