Glossary of Chromosome, Gene and DNA Terms and Terminology

  • Chromosome: A cell that contains protein and one DNA molecule and that is found in the nucleus of the cell
  • Nucleotides: The basic cells that serve as the building blocks of both RNA and DNA.
  • DNA: Deoxyribonucleic acid, a nucleic acid, long molecule and macromolecule
  • RNA: Ribonucleic acid, a nucleic acid, long molecule and macromolecule
  • Gene: The part of the DNA that encodes information
  • Autosome: A sex chromosome
  • Allosome: Also referred to as an allosomal chromosome or a body chromosome is a non sex chromosomes despite the fact that allosomes do play a role in sexual determination for males and females.
  • Prokaryotes: A types of cell that does not have organelles or a nucleus
  • Eukaryotes: The type of cell that has a nucleus containing genetic material and organelles

Chromosomes

Organization of DNA in a eukaryotic cell.

Simply defined, a chromosome is a cell that, has shown in the picture above, contains protein and one DNA molecule that is found in the nucleus of the cell.

Nucleotides are the basic cells that serve as the building blocks of both RNA and DNA. Nucleotides in DNA are referred to as A, C, G and T that are connected to each other in an array with hydrogen bonds; it is A, C, G and T are the nucleotides that contain our information.

DNA is deoxyribonucleic acid RNA is ribonucleic acid (RNA); and, both deoxyribonucleic acid and ribonucleic acid are nucleic acids, long molecules and macromolecules.

It is the DNA that contains genetic material and genetic information. It is the DNA that is used to determine paternity and to solve crimes when blood and other evidence are left at a crime scene because it is this DNA that contains a person's unique genetic identity.

Cells are classified as prokaryotes and eukaryotic cells. Prokaryotes, one of the two types of cells, do not have organelles or a nucleus; and eukaryotes, on the other hand are the type of cell which have a nucleus containing genetic material and organelles. Eukaryotic cells, therefore, have chromosomes in their nuclei and prokaryotes have no chromosomes because they lack the chromosome containing nuclei.

Chromosomes are made of DNA double helix strands that are wrapped around proteins; chromosomes contain and carry genetic and hereditary information.

The two types of chromosomes are the:

  • Autosomes or autosomal chromosomes
  • Allosomes or allosomal chromosomes

There are two copies of each autosome (chromosomes 1-22) in both females and males. The sex -*chromosomes are different: There are two copies of the X-chromosome in females, but males have a single X-chromosome and a Y-chromosome.

Autosomes

Autosomes are the sex chromosomes; and all the other chromosomes in the body, other than the sex chromosomes, are allosomes or allosomal chromosomes. Although allosomes are not sex chromosomes, allosomes do play a role in sexual determination for males and females. At times, autosomal chromosomes are referred to as body chromosomes and allosomal chromosomes are sometimes referred to as sex chromosomes.

Every species has a distinctive and specific number of chromosomes and also a specific pattern of chromosomes for all sets of its chromosomes. The specific pattern of chromosomes is referred to as a karyotype.

Human beings have 22 pairs of autosomal chromosomes and one pair of allosomal chromosomes. Under normal circumstances, human beings have a total of 23 pairs of chromosomes, totaling a complete set of 46 chromosomes. Autosomal chromosomes are identified and labeled with numbers from 1 to 22; and allosomal chromosomes are identified and labeled with the letters X and Y only.

The female gender has a diploid genome of XX and males have a diploid genome of XY. When there is any variation in this XX and XY characteristic, it is considered abnormal. For example, a third chromosome number 21 is called trisomy 21, which in the past was called Down syndrome.

Genes

A gene is a region of DNA that encodes function. A chromosome consists of a long strand of DNA containing many genes. A human chromosome can have up to 500 million base pairs of DNA with thousands of genes.

The different nucleotides of our DNA sequences among all human beings form genes. Genes are the basis of heredity. These sequences are called genotypes.

At times, the results of our genetic makeup are obvious and visible to the naked eye and, at other times, these genetic traits are not at all obvious and visible to the naked eye. For example, the color of our eyes is obvious and visible to the naked eye but our genetic risk factors for some diseases and disorders are not obvious and visible to the naked eye.

At times, genes can become abnormal in terms of their sequencing. These abnormalities are called genetic mutations.

DNA

The chemical structure of a four base pair fragment of a DNA double helix. The sugar-phosphate backbone chains run in opposite directions with the bases pointing inwards, base-pairing A to T and C to G with hydrogen bonds.

DNA, or deoxyribonucleic acid, Is the foundation and the molecular basis of inheritance. DNA is the macromolecule, as discussed above with other macromolecules, that encodes information in the body and it also provides the basis for instructions to body in terms of its protein production. DNA is a twin chain, or double helix chain, that is comprised of a sugar group which is called deoxyribose, a phosphate group and a base of guanine, cytosine, thymine or adenine. Each strand or chain of DNA in the double helix is referred to as a polynucleotide. Polynucleotides are made up from monomers called nucleotides.

As previously stated, the nucleotides in our DNA are referred to as A (adenine), C (cytosine), G (guanine) and T (thymine) that are connected to each other in an array and formation with hydrogen bonds; it is the A, C, G and T nucleotides that contain our information.

A (adenine) is paired with T (thymine) and held together with 2 hydrogen bonds; and, C (cytosine) is paired with G (guanine) and held together with 3 hydrogen bonds, as shown in the picture above. The relatively complex process of reading and deciphering DNA is done with a 3' to 5‘ reading. The 3' and 5' ends are the opposite ends of each DNA strand.

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