ions -DNA replication minimizes errors such as the DNA that is duplicated but changes in the DNA do occur, producing mutations. Although most mutations are either neutral or harmful they are also the raw material for evolution. Such mutations from alleles, alternate forms of a given gene that may produce differences in structure or function such as black, brown or blond hair in humans, or different mating calls in frogs.
Stages of Mitosis~
2)Chromosomes make identical copies of themselves.
3)They line up along the centre.
4)They move apart.
5)Two daughter cells form with identical chromosomes to the parent cell.
Homologous chromosomes have the same genes, but each homologue may have the same alleles of some genes and different alleles others.
The cell cycle is tightly controlled. Both during the embryonic development and during the maintenance and repair of the adult body, progressing through the cell cycle is regulated primarily by two interacting processes. (1)Production of, and responses to, growth factors that generally speed up the cell cycle; (2)Intracellular checkpoints that stop the cell cycle if problems such as mutations in the DNA or misalignment of the chromosomes have occurred. Most cancers develop because one of both of these processes goes awry.
Many different molecules control the cell cycle;
Porto-oncogenes:Any gene whose proteins tends to promote mitotic cell division if called a proton-oncogene. The genes for growth factors, grow factor receptors, and some cyclins and Cdks are proton-oncogenes. In most cases, progress through the cell cycle beings when a growth-stimulating protein such as epidermal growth factor (EGF) binds to a receptor on the surface of a cell. This stimulates the synthesis of cyclins which bind to Cdks and activate them. Thus, these proton-oncogenes are essential to the normal control of the cell cycle. Tumor suppressor genes:The protein products of tumor suppressor genes prevent...
Please join StudyMode to read the full document