20 chromosomes.
A cell with 40 chromosomes going through meiosis will result in individual haploid cells with 20 chromosomes each.
After the first nuclear and cellular division in meiosis, each cell will already have 20 chromosomes each, since homologous chromosomes are separated at Anaphase I in Meiosis I. After the second nuclear and cellular division in meiosis, each cell will have 20 chromosomes as well, since the sister chromatids of each of the 20 chromosomes are separated during Anaphase II in Meiosis II.
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