What are the differences between DNA, Gene, Allele, Genome, and Chromosome?
DNA
Deoxyribonucleic Acid or as known as DNA is the chemical compound that contains the instructions needed to develop and direct the activities of nearly all living organisms. DNA consists of two long strands of polynucleotides that twist around each other clockwise in a double helix. Nucleic acid bases attached to the sugar groups of each strand face each other within the helix, perpendicular to its axis. Only four bases exist: the purines, include adenine and guanine (A and G); and the pyrimidines, include cytosine and thymine (C and T). During assembly of the double helix, stable pairings of nucleotides from either strand are made between A and T or between G and C. Each base pair is joined together by hydrogen bonds. The beginning of each strand DNA called 5’ (five prime); and the end of strand called 3’ (three prime). Each other of the two strands run in the opposite direction (antiparallel) so that one runs 5’ to 3’ and one runs 3’ to 5’, called the sense strand and the antisense strand, respectively. The strands are separated during DNA replication (We'll discuss it later ^^). Each base pair (bp) forms one of the billions of rungs in the long, unbroken ladder of DNA that forms a chromosome.
Gene and Allele
A gene is a length of DNA within the genome that code for a specific proteins. It is containing the instructions for our individual characteristics, like eye and hair colour. It is just like a sentence in one paragraph that is responsible for a given feature or protein.
Genes establish in different forms, called alleles (some alleles come in pairs, and predisposed to our characteristics). Alleles can be dominant or recessive. It is dominant if:
(1) the characteristics are fully expressed in an organism's phenotype (trait);
(2) genotype (symbol representation) represented by any capital letter (ex: if brown eyes is dominan, code by B or F, T).
It is recessive if:
(1) the characteristics may not be fully expressed in an organism's phenotype.
(2) genotype represented by any lower case letter (ex: b, f, t).
Genome
An organism's complete set of DNA is called its genome. If we picture genes like sentences (or any sequence of characters that mean something) then we can picture the genome as a whole book.
Chromosome
Chromosomes contains a long strand of DNA, tightly package around proteins called "histones". Humans have 23 pairs of chromosomes. The other 22 pairs are autosomes (non-sex chromosomes) and look the same for both males and females. The DNA making up each of our chromosomes contains thousands of genes. At the ends of each of our chromosomes are sections of DNA called telomeres. Telomeres protect the ends of the chromosomes during DNA replication by forming a cap, much like the plastic tip on a shoelace.
References
Niederhuber, J.E., Armitage, J.O., Doroshow, J.H., Kastan, M.B., and Tepper, J.E., Abeloff's Clinical Oncology 5th Edition, Philadelphia, Elsevier.