Explain why gene expression may be decreased when histones are deacetylated/dna is methylated.

DNA acetylation and methylation are important for the proper gene expression. These modification works as epigenetics modification in the genome of the organism.

The histone deacetylation means the removal of acetyl group at particular amino acid residues. The deactylation of histones maintains the positive charge on the histone and bind them tightly with neighboring nucleosome result in decrease in gene expression. The methylation of DNA is the addition of methyl group at particular site on DNA molecule. The methylation results in the lack of gene expression and decreases the gene expression.

meteorologists would compare a new weather map with one 24 h old to see how fast a front is moving.

a- all cells come from pre-existing cells