Second purpose of DNA create new Second purpose of DNA create new Mitosis Mitosis cells cells forfor 1 growth 1 growth 2 repair 2 repair 3 replacement 3 replacement Mitotic divisions enable Mitotic divisions enable somatic cells to increase in somatic cells to increase in number or to be replaced number or to be replaced Only somatic cells undergo mitosis Only somatic cells undergo mitosis Somatic cells as opposed to sex cells Somatic cells as opposed to sex cells have 46 chromatids have 46 chromatids There are 2 types of cells in your body There are 2 types of cells in your body that are not somatic cells that are not somatic cells red blood cells which have no nuclei and do red blood cells which have no nuclei and do not undergo mitosis and not undergo mitosis and sex cells gametes which only 1 chromatid sex cells gametes which only 1 chromatid per chromosome per chromosome Each chromosome is Each chromosome is composed of 2 chromatids composed of 2 chromatids Chromatids exist in pairs called Chromatids exist in pairs called chromosomes chromosomes The two chromatids in a chromosome The two chromatids in a chromosome each have the same set of genes each each have the same set of genes each specifying the same function specifying the same function One chromatid in each chromosome One chromatid in each chromosome comes from each of your biological comes from each of your biological parents parents DNA is found DNA is found in the in the nucleus nucleus DNA double helix unwound S U G A R A T S U G A R S U G A R S U G A R S U G A R S U G A R S U G A R T G C A S U G A R C G S U G A R S U G A R S U G A R S U G A R Nuclear Nuclear membrane membrane dissolves dissolves S U G A R S U G A R S U G A R A T G C T A S U G A R C G S U G A R S U G A R S U G A R S U G A R S U G A R S U Humans have 46 chromatids sorted G into 23 pairs chromosomes A R S U G A R S U G A R Each chromosome separates into 2 individual chromatids Within these the DNA double helix separates into 2 individual DNA strands A T S U G A R S U G A R S U G A R Free nucleotides S U G A R S U Each strand of DNA attracts G complementary nucleotides A R T G C S U G A R S U G A R S U G A R S U G A R S U G A R A S U G A R C G Two strands of DNA have now become four 46 chromatids have now become 92 A T G C S U G A R S U G A R S U G A R S U G A R S U G A R S U G A R S U G A R S U G A R T A S U G A R S U G RC A S U S G U A G A R R G S U G A R S U G A R S U G A R S U G A R A T G C T A C S U G A R S U G A R S U G A R S U G A R S U G A R S U G A RG 46 chromatids have become 92 They separate into 2 sets of 23 chromatid pairs chromosomes Each set of 23 chromosomes moves to opposite poles New cell membranes form A new cell membrane has formed around each of two new cells A nuclear membrane forms around each set of 23 chromosomes The original cell has now become 2 cells MUTATIO N Theoretically each new daughter cell has the identical sequence of DNA found in the parent cell However every time replication takes place review slides 5 7 the possibility of error is introduced These errors are called mutations mutations See the protein production 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 Result every cell in the daughter lineage will carry the mutation lineage will carry the mutation Effects Effects 1 If the error occurs in an exon it may affect protein 1 If the error occurs in an exon it may affect protein production This may have production This may have No effect because of redundancy of codons that produce No effect because of redundancy of codons that produce each amino acid each amino acid An effect on the protein product or cell building block An effect on the protein product or cell building block produced by all daughter cells produced by or deformed cells or deformed cells all daughter cells This may lead to ineffective This may lead to ineffective 2 If the error occurs in an intron the effect could be 2 If the error occurs in an intron the effect could be No effect For example if a junk gene has no function No effect For example if a junk gene has no function natural selection has no effect on variants of that gene More natural selection has no effect on variants of that gene More about this later about this later An error in a regulatory gene homeobox gene etc which An error in a regulatory gene homeobox gene etc which may lead to cell death cancer or other major malformations may lead to cell death cancer or other major malformations A mutation A mutation herehere A functional unit of DNA will ultimately affect this a gene chromatid chromosome A T T A C G G C A T T A C G G C etc etc Mutations in embryonic Mutations in embryonic somatic cells stem cells somatic cells stem cells The earlier in the process of embryo The earlier in the process of embryo formation the error occurs the formation the error occurs the greater the percentage of cells that greater the percentage of cells that will be affected mutation will be affected later earli er 25 of all cells carry the mutation possibly disastrous 1 of 32 cells has the mutation Serious but maybe not fatal Summary Summary Mitosis produces new cells for Mitosis produces new cells for growth growth repair repair replacement replacement Theoretically new daughter lineages Theoretically new daughter lineages should be genetically identical to the parent should be genetically identical to the parent cellcell Mutation can happen when DNA is Mutation can happen when DNA is replicated replicated Results may be anywhere from negligible to Results may be anywhere from negligible to catastrophic catastrophic