Each parent contributes 23 chromosomes to their offspring via the gametes they contribute egg or sperm. Humans have 46 chromosomes in all, comprised of two sets of twenty-three. The bulk of the DNA in cells is located in the cell's nucleus in the form of chromosomes. Some examples include doxorubicin, cyclophosphamide, carboplatin, cisplatin, topotecan and etoposide (VP-16). Since cancer cells are often rapidly dividing, this phase of the cell cycle is the target of many of the chemotherapy agents that will be described in the 'Cancer Treatments' section. The processes by which mutations are generated will be dealt with in the 'Causes of Mutation' section.Īll dividing cells must go through the process of DNA replication. There are several cancer types that are associated specifically with the breakdown of the repair processes that normally function during DNA replication. Accumulations of mutations can lead to the development of cancer. Mistakes that occur during DNA replication can lead to the generation of cells with mutated genes. Human cells have evolved several mechanisms to correct errors of this type but they are not perfect. If these changes occur within genes, they can alter the function of the cell. Remember that the X-shaped molecule is really composed of two copies of one chromosome.Įrrors may occur during replication that lead to changes in the nucleotide sequence of the chromosomes. The process is depicted in schematic form below. Since this is the form of chromosomes that is easiest to isolate and visualize, this is the structure with which most people are familiar. The replicated chromosomes contain two identical strands of DNA that remain attached until they become separated toward the end of mitosis (in anaphase).
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