Causes Postzygotic mutation

post- zygotic changes genome can caused small mutations affect single base pair, or large mutations affect entire chromosomes , divided 2 classes, spontaneous mutations , induced mutations.

spontaneous mutations

depurination mutation results in 1 normal strand , 1 shortened strand after replication.

most spontaneous mutations result of naturally occurring lesions dna , errors during in dna replication without direct exposure agent. few common spontaneous mutations are:

depurination- loss of purine (a or g) base form apurinic site. apurinic site, known ap site, location in genetic sequence not contain purine base. during replication, affected double stranded dna produce 1 doubled-stranded daughter containing missing purine, resulting in unchanged sequence. other strand produce shorter strand, missing purine , complementary base.
deamination- amine group on base changed keto group. results in cytosine being changed uracil , adenine being changed hypoxanthine can result in incorrect dna replication , repair.
tautomerization- hydrogen atom on nucleotide base repositioned causing altered hydrogen bonding pattern , incorrect base pairing during replication. example, keto tautomer of thymine pairs adenine, enol tautomer of thymine can bind guanine. results in incorrect base pair match. there amino , imino tautomers of cytosine , adenine can cause incorrect base pairing other nucleotides.

induced mutations

induced mutations lesions in dna caused agent or mutagen. mutagens demonstrate mutational specificity, meaning cause predictable changes in dna sequence. few common mutagens induce mutations are:

ultraviolet light (uv)- causes pyrimidine (t or c) nucleotide bases on same strand covalent join forming pyrimidine dimer. thymine-thymine dimers common mutation caused uv light. since dimers cause disruptive kink in dna structure, polymerases have trouble reading region, slowing down dna replication.
base analogs- chemical compounds sufficiently similar in structure , chemistry nitrogenous bases of dna, such able incorporated in sequence. these analogs not have same pairing properties of normal bases, therefore can pair incorrectly nucleotides during replication. 5- bromouracil (5-bu) common analog thymine, enol form of 5-bu still able bind adenine. ionized form, on other hand, pairs guanine.
intercalating agents- chemical compounds place between stacked nitrogenous bases in dna, causing frameshift mutation. intercalating agents, duanorubicin, capable of blocking replication , transcription, making them incredibly toxic proliferating cells.
reactive oxygen species (ros)- highly reactive oxygen- containing molecules capable causing dna strand breaks , many damaging effects cellular components.
alkylating agents- compounds attach alkyl group 4 bases. when alkyl group added guanine, can lead incorrect pairing thymine , disrupt accuracy of replication.




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