Which occurs during transcription? dna is copied to create a second dna strand. mrna codons and trna anticodons assemble amino acids. dna is unzipped with the aid of dna polymerase. mrna is synthesized from a strand of dna.

During transcription, mRNA is synthesized using DNA as a template. This process usually takes place in the cell nucleus and is carried out with the help of an enzyme called RNA polymerase.

mRNA  plays the role of a messenger hence the term messenger RNA or  mRNA in short. Information for synthesis of a specific protein is transcribed on mRNA in the nucleus of the cell. The mRNA then leaves the nucleus and enters the cytoplasm and attaches onto a  ribosome. Ribosomes are cell structures fondly called the "work bench " of the cell.

It is in the ribosomes that the information brought by mRNA is translated or decoded and used to synthesize the specific protein that was coded for.  

a tetrad is the foursome during meiosis made by two homologous chromosomes that have each already replicated into a pair of sister chromatids.

if the type of the food available changes, then the frequency of beak types will change, because birds with beaks more suited to the available food will be more successful over time.