DNA or deoxyribonucleic acid is the hereditary molecule in all living cells. It is the blueprint for life that is made up of two strands attached together as a double helix. It consists of four nucleotides made up of a base, sugar and phosphate; the bases are adenine (A), cytosine (C), guanine (G), and thymine (T), shortened to ACGT.
Cells are the smallest structural units of living matter and consist of a nucleus and organelles that perform essential tasks that keep the cells alive. Plants and trees, fish, animals, and of course humans consist of an enormous number of cells coordinating with one another. We also know of the existence of single cell organisms such as yeast or bateria. A well studied unicellular organism is the microbe amoeba.
Genes are made of DNA and contain enough DNA to code for one protein. Specific genes launch instructions to make molecules known as proteins. We also possess genes that do no perform this function.
Proteins are large, complex molecules , the “workers” that do most of the work in cells and are required for the structure, function, and regulation of the body’s tissues and organs. They consist of hundreds or thousands of smaller units called amino acids, which are attached to one another in long chains. There are 20 different types of amino acids that can be combined to make a protein. The sequence of amino acids determines each protein’s unique 3-dimensional structure and its specific function.
The DNA contains the code of instructions on how and which proteins have to be made but it does not leave the cell. DNA delegates this task to the ribonucleic acid RNA.
The process of the making of a protein is complex and involves two major steps: transcription and translation that together are called gene expression. During transcription, the double strand or double helix of the gene’s DNA unzips itself and passes the information that is stored in each of the strands to RNA in the cell nucleus; this information is a copy of the strands of the DNA of a gene. The RNA that now contains the information for making the protein is called messenger RNA or mRNA because it carries the message from the DNA out of the nucleus to the cytoplasm of the cell; cytoplasm is a thick solution that fills each cell and is enclosed by the cell membrane. The second step occurs in the cytoplasm. It is here that the mRNA interacts with the ribosome that reads the sequence or genetic code of the mRNA nucleotide. Ribosomes are particles consisting of RNA and associated proteins that function to synthesize proteins and are therefore called protein factories. A sequence of three nucleotides, called a codon, usually codes for one particular amino acid. 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 nucleotides that does not code for an amino acid).
The flow of information from DNA to RNA to proteins is one of the fundamental principles of molecular biology. It is so important that it is sometimes called the “central dogma.”
There are three main differences between DNA and RNA. The DNA is double stranded whereas the RNA is single stranded. A second major difference is that the DNA’s thymine is replaced by uracil in RNA. Thymine makes the DNA more stable whereas uracil requires less energy to maintain than thymine. The third difference is that DNA contains the sugar deoxyribose, while RNA has the sugar ribose.
The sum total of an organism's DNA is called a genome.
Genetics studies how individual genes or groups of genes are involved in health and disease.
In Genetic Genealogy, we combine a genetic analysis with genealogical research such as a traditional family tree, to study and understand family history. It is used in forensics to identify the DNA of an individual and link that person to a family, a missing person, or even a criminal.
The ultimate source of all genetic variation is mutation.
Mutation is important as the first step of evolution because it creates a new DNA sequence for a particular gene, creating a new allele. Recombination also can create a new DNA sequence (a new allele) for a specific gene through intragenic recombination. Mutations are irreversible which is why they can be passed on to the next generation.
The four classes of mutations are (1) spontaneous mutations (molecular decay), (2) mutations due to an error in replication (3) errors introduced during DNA repair, and (4) induced mutations caused by mutagens i.e. agents that cause a mutation.
Migration is determined by tracking the movement of specific alleles. This is what the National Geographic’s Genographic project set out to do on a global scale and has now expanded to numerous other projects by different companies. Migration can also be estimated indirectly by assessing the extent of genetic differentiation among subpopulations.
A haplotype is a group of alleles that are inherited together from a single parent whereas a haplogroup is a group of similar haplotypes that share a common ancestor. In other words, a haplogroup is a combination of alleles at different chromosomal regions that are closely linked and that tend to be inherited together. As a haplogroup consists of similar haplotypes, it is usually possible to predict a haplogroup from haplotypes.
In human genetics, the haplogroups most commonly studied are Y-chromosome (Y-DNA) representing the patrilinieal line and mitochondrial DNA (mtDNA) representing the matrilineal line.
DNA is located in the nucleus of cells in chromosomes and in smaller amounts in mitochondria. Humans possess about 25 thousand genes that as we have seen earlier are together called a genome i.e. the total sum of an organism’s DNA. A genome is thus the instruction manual that contains genetic information in about 3 billion bases. It is this instruction manual that ensures that humans can only produce human babies and elephants can only produce baby elephants.
A chromosome is made up of a single DNA strand or helix on which the genes are located. Humans have 23 pairs of chromosomes, one strand from each parent with a total of 46.
22 of the chromosomes are similar and are known as autosomal whereas the 23rd pair of chromosomes differs between men and women. In women, these chromosomes are similar and shaped like an X, the chromosomal pair is an XX. The two chromosomes in men are shaped as an X and a Y, the chromosomal pair is an XY. In addition to to Y-DNA and mtDNA analyses, autosomal DNA i.e. an analysis of the 22 analogous chromosomes can also be routinely carried out.
To summarise: DNA that contain the code for a specific protein are located in our genes and the genes are located in our chromosomes.
