Theseerrorsarecalled mutations

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Unformatted text preview: ughter cell has the identical sequence of DNA found in the parent cell. However, every time replication takes place (review slides 5­7), the possibility of error is introduced. These errors are called mutations. See the Mutation PP presentation to review the types of mutations that can occur. BUT WHAT IF THERE ARE MUTATIONS DURING MITOTIC DIVISIONS? Errors in mitosis: Errors in mitosis: • Result: every cell in the daughter lineage will carry the mutation. • Effects: • 1.) If the error occurs in an “exon”, it may affect protein production. This may have: – No effect (because of redundancy of codons that produce each amino acid). – An effect on the protein product or cell building block produced by all daughter cells. This may lead to ineffective or deformed cells. • 2.) If the error occurs in an “intron”, the effect could be – No effect. For example, if a “junk” gene has no function, natural selection has no effect on variants of that gene. More about this later. – An error in a regulatory gene, homeobox gene, etc., which may lead to cell death, cancer or other major malformations. A mutation here A functional unit of DNA A G G C A T T A C G G chromatid A C a gene T T will ultimately affect C etc. etc. this chromosome Mutations in embryonic somatic Mutations in embryonic somatic cells (stem cells): • The earlier in the process of embryo formation the error occurs, the greater the percentage of cells that will be affected. mutation later 1 of 32 cells has the mutation. Serious, but maybe not fatal. earlier 25% of all cells carry the mutation: possibly disastrous. Summary Summary • Mitosis produces new cells for – – – growth repair replacement • Theoretically, new (daughter) lineages should be genetically identical to the parent cell • Mutation can happen when DNA is replicated. • Results may be anywhere from negligible to catastrophic....
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