Mitosis

• When replicated, sister chromatids are joined at the centromere
• Homologous pairs are the maternal and paternal versions of each chromosome
• asexual reproduction prevents cancer and offspring are suited to favourable conditions, it is very fast
• asexual reproduction doesnt provide a large gene pool so offspring as susceptible to disease, offspring are less able to adapt to change
• During G1, the cytoplasm grows and organelles are replicated
• During the S phase, DNA is replicated
• During G2, proteins for mitosis are synthesised
• In prophase, the centrioles move to the cells poles, the nuclear envelope begins to degrade and chromosomes condense
• In metaphase, chromosomes line up at the centre of the cell and spindle fibres begin to extend
• In anaphase, the spindle fibres connect to the centromeres of the chromosomes and begin to drag them to the poles of the cell
• In telophase, the nuclear envelope reforms at each pole around the chromosomes, the cell begins to cleave
• In cytokinesis, the cell divides into two daughter cells with identical sets of DNA
• When splitting, animal cells cleave, plant cells form a cell plate and bacteria form septums
• The mitotic index is the number of cells undergoing mitosis in a sample
• Both benign and malignant tumours can cause damage to the body in the form of blockages, putting pressure on organs and metastasis in malignant tumours
• Malignant tumours have coarse chromatin, more and larger nuclei, and irregularly shaped cytoplasm
• Protooncogene promotes cell division
• Protooncogene can mutate into oncogene, causing uncontrolled cell division promotion
• Tumour suppressor gene prevents cell division when an error is detected
• Tumour suppressor gene can mutate where it will no longer prevent cell division, causing uncontrolled cell division
• Cancer can be treated with surgery, chemotherapy and radiotherapy
• Radiotherapy is where radiations are used to damage cancer cells causing cell death
• Chemotherapy is where chemicals are used to interrupt replication in the S phase preventing DNA replication and in anaphase preventing the splitting of sister chromatids
• Cancer drugs are not given more frequently to allow healthy cells to recover between doses
• In the root tip squash, onion roots are placed in hydrochloric acid to break down the cell walls, allowing dyes to access the chromosomes, they are then crushed to 1 cell thick for viewing