Chromosome Mechanics

Abstract

Abstract Chromosome mechanics describes the processes of chromosome replication and interactions during somatic cell division and gametogenesis. Mitosis can be divided into two phases consisting of nuclear and cytoplasmic division ultimately producing identical diploid somatic cells. Segregation during mitosis is largely dependent on chromosomal attachment to the mitotic spindle with a fully developed kinetochore structure. This is in contrast to meiosis where cells undergo two rounds of nuclear division to produce haploid germ cells. During this process, homologous chromosomes pair at the cellular midline allowing for exchange of deoxyribonucleic acid (DNA) between parental alleles and stabilisation of the chromosome structures during separation. Aberrations occurring in either mitosis or meiosis can result in numerical abnormalities (from nondisjunction events) which often result in nonviable offspring. However, there are some aneuploidies that are viable with trisomy 21 being the most common example of this. Similarly, unrepaired DNA damage resulting in chromosomal breakage and structural rearrangements. These large‐scale genetic changes reduce the genetic efficacy of a cell ultimately leading to cancer or cell death. In summary, mitosis and meiosis are integral parts of the cellular life cycle and both processes are essential at maintaining genomic stability within an organism. Key Concepts The cell cycle comprises two main phases: mitosis, where cell division occurs, and interphase, which includes DNA replication and the expression of many essential proteins. Interphase can be further divided into G1, S and G2. Cyclin‐dependent kinases regulate progression through the cell cycle at three major checkpoints: G1, G2 and a spindle checkpoint during mitosis. Mitosis is the process of cell division resulting in two identical diploid cells and can be divided into prophase, metaphase, anaphase and telophase. Meiosis is the process of cell division that results in germline cells where following one round to DNA replication, the cell undergoes two cell divisions. Meiosis in males results in four identical haploid cells, while meiosis in females produces a single mature ovum and three polar bodies. Aberrations in either mitosis or meiosis can result in nondisjunction resulting in aneuploidy. Defects in DNA repair mechanisms can also result in chromosome damage or breaking which will negatively impact the process of cell division.