Explain how in vitro mutagenesis and rna interference to discover the functions of some genes

In vitro mutagenesis:

Another way of applying cloned DNA is in vitro mutagenesis. Here, a mutation is caused in a fraction of cloned DNA which is then transferred to the cell or organism, in order to determine the results of the mutation.

Disable cloned gene, when it's inserted back in the organism, it can be used to study phenotype.

rna interference:

RNA interference (RNAi) uses RNA molecules to prevent gene expression or translation causing in

inactivation of the targeted mRNA molecules.

It gives Double-stranded RNA homologous to remote gene which will cause a disintegration of mRNAs out of the gene.

any abiotic or biotic factor in an ecosystem that causes a population's size to slow or decrease is a limiting factor.

what is this saying?