reproduction sexual asexual chromosomes histones nonhistones deoxyribonucleic helix supercoil eukaryote nucleus nucleotides autosomes homologous centromere diploid haploid karyotype fission prokaryote mitosis meiosis interphase metaphase prophase anaphase telophase cytokinesis centriole spindle cleavage wall gamete synapsis tetrad assortment oogenesis spermatogenesis spermatids ootids