A parent cell goes through two divisions to produce sperm or ova.
Explanation:
In the sex cells process of meiosis occurs and form four haploid cells which are egg in female and sperm in male. These are called gametes.
Gametes have one chromosome each, on which genes are there.
The genes on the homologous chromosome from parents will cross over, the resulting trait will be on allele expressed.
Sometimes the error can happen in meiosis of germ or sex cells and two chromosomes can be in one cell, and hence the resulting gamete can have three chromosomes which can cause abnormality in the foetus.
The haploid cells of the organism when fuses in fertilization the zygote is formed. The zygote undergoes several divisions to form embryo and then an organism.
