This document summarizes molecular mechanisms of mutation and DNA damage repair in cells. It discusses how mutagens can induce point mutations by substituting or damaging DNA bases, causing errors during DNA replication. It also describes genetic diseases like fragile X syndrome that result from expansions of trinucleotide repeats. The document outlines several DNA repair pathways in cells and how defects in these pathways can lead to increased mutation rates and cancer-prone genetic disorders.

1. MOLECULAR BASIS OF MUTATION KISHOR SAWAIKAR R A C WASHIM (MS) INDIA

10. Molecular Basis of Gene Mutation Mutations are changes in the DNA sequence of genes. Point mutations typically refer to alterations of single base pairs of DNA or of a small number of adjacent base pairs. Mutations in DNA caus e substitutions in protein

21. <> X-linked inheritance Asymptomatic, hemizygous fathers pass &quot; fragile X &quot; chromosome to daughters Heterozygous daughters transmit to 1/2 of sons, who show syndrome 1/2 of daughers are carriers Syndrome becomes more pronounced in successive generations expansioin of repeat occurs in female germline # CGG repeats Geno / Phenotype 6 ~ 54 standard ~ 55 ~ 200 carrier > 200 Fragile-X Syndrome