A nucleus within an ascus undergoes meiosis, producing four haploid spores, which then undergo mitosis, producing eight haploid ascospores. These haploid ascospores contain a maximum of different genetic types.

Four.

Explanation:

Initially four haploid spores are produced by meiosis. We know that during meiosis pairing between homologous chromosomes occurs and this created genetic difference between the divided cells. Exchange of genetic material doesn't occur during mitosis so mitotically divided cells are similar. Thus when spores divide by mitosis and become eight in number, here will be no new genetic difference.

The complete sentence will be -

A nucleus within an ascus undergoes meiosis, producing four haploid spores, which then undergo mitosis, producing eight haploid ascospores. These haploid ascospores contain a maximum of four different genetic types.

answer:

convection currents in the magma drive plate tectonics. heat generated from the radioactive decay of elements deep in the interior of the earth creates magma (molten rock) in the aesthenosphere. the aesthenosphere (70 ~ 250 km) is part of the mantle, the middle sphere of the earth that extends to 2900 km.