How does mutation affect DNA replication?
Mutation means changes in genetic material that would be inherited. Mutation within a gene alters the recipe for protein. Mutation in chromosome may change the way genes are expressed.
In any case, error in DNA replication is there.
There could be point mutations which do not affect appearance of chromosome. There are changes in one base-pair of DNA, it could be addition or deletion of bases as well. Base substitution changes only one codon representing an amino acid in the protein that the gene codes for; but addition or deletion causes 'frame shift' mutation, i.e. sequence of amino acids change completely after mutated region.
Structural addition, deletion, duplication, inversion or translocation of chromosomal parts are also mutation.
The above types of mutations will definitely cause random errors in DNA replication in the progeny.
Mutation may be associated with change in chromosome number as happens in case of trisomy of chromosome number 21 . The child with Down syndrome receives three 21 chromosomes (hence 47 instead of 46 chromosomes), generally one extra through mom's egg.
Though we generally discuss mutations which cause diseases, mutations are not always bad. After all mutations provide new variations to a population.