Red Blood cells

A gene is a segment of DNA that is involved in producing a polypeptide chain; it can include regions preceding and following the coding DNA as well as introns between the exons; it is considered a unit of heredity.

Its function is to carry out protein synthesis. Protein synthesis is when amino acids are linked together in peptide chains which are dictated by the sequence of nucleotides  in DNA; this governing sequence is conveyed to the synthesizing apparatus in the ribosomes by mRNA, which is formed by base-pairing on the DNA template.

Here is a lengthy web definition in more detail: During the process of transcription, the information stored in a gene’s DNA is transferred to a similar molecule called RNA (ribonucleic acid) in the cell nucleus.

Translation, the second step in getting from a gene to a protein, takes place in the cytoplasm. The mRNA interacts with a specialized complex called a ribosome, which “reads” the sequence of mRNA bases. Each sequence of three bases, called a codon, usually codes for one particular amino acid. (Amino acids are the building blocks of proteins.) A type of RNA called transfer RNA (tRNA) assembles the protein, one amino acid at a time. Protein assembly continues until the ribosome encounters a “stop” codon (a sequence of three bases that does not code for an amino acid).

It is controlled by separate transcriptional controls on each gene. A transciptional control controls a gene expression by controlling the number of RNA transcripts of a region of DNA. This is a major regulatory mechanism for differential control of protein synthesis in both pro and eukaryotic cells. 

Red blood cells originally have a nucleus when they are formed in the bone marrow but their nucleus disintegrates so that the cell can hold more oxygen and because the nucleus consumes the most oxygen from all the cell organelles. A web definition of red blood cells: a mature blood cell that contains hemoglobin to carry oxygen to the bodily tissues; a biconcave disc that has no nucleus.