Around 1595, the compound microscope (utilizing more than one lens) was invented. In 1665, Robert Hooke an English natural philosopher, architect, scientist and polymath was the first to identify cells with a microscope. In 1673, Anton van Leeuwenhoek was the first person to observe and describe single celled organisms, which he originally referred to as animalcules (which we now refer to as microorganisms). He was also the first to record and observe muscle fibers, bacteria, spermatozoa and blood flow in capillaries (small blood vessels). In 1953, James Watson and Francis Crick discovered of the double helix, the twisted-ladder structure of deoxyribonucleic acid (DNA), which marked a milestone in the history of science and gave rise to modern molecular biology, which is largely concerned with understanding how genes control the chemical processes within cells. Their discovery yielded ground-breaking insights into the genetic code and protein synthesis. DNA is the carrier of our genetic information, and it is passed down from generation to generation. All of the cells in our bodies, except red blood cells, contain a copy of our DNA.
At conception, a person receives DNA from both the father and mother. We each have 23 pairs of chromosomes. These 23 pairs of chromosomes are known as nuclear DNA because they reside in the nucleus of almost every cell in our body. Most human DNA is packaged in chromosomes within the nucleus, however mitochondria also have a small amount of their own DNA. This genetic material is known as mitochondrial DNA or mtDNA. Mitochondria are structures within cells that convert the energy from food into a form that cells can use. Each cell contains hundreds to thousands of mitochondria, which are located in the fluid that surrounds the nucleus called the cytoplasm.
Mitochondria produce energy through a process called oxidative phosphorylation. This process uses oxygen and simple sugars to create adenosine triphosphate (ATP), the cell’s main energy source. A set of enzyme complexes, designated as complexes I-V, carry out oxidative phosphorylation within mitochondria. In school all students learn that “Mitochondria is the Powerhouse of the Cell”, because they act like a digestive system which takes in nutrients, breaks them down, and creates energy rich molecules for the cell. The biochemical processes of the cell are known as cellular respiration. Many of the reactions involved in cellular respiration happen in the mitochondria. Mitochondria are the working organelles (tiny cellular structure that performs specific functions) that keep the cell full of energy.
Human genetic variation is the genetic differences in and among populations. There may be multiple variants of any given gene in the human population (alleles or one of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome), a situation called polymorphism. Everyone’s genome (organism’s complete set of DNA, including all of its genes) contains millions of genetic variations, or variants, that make each person unique. Some contribute to the differences between a certain human’s eye color or blood type. A small number of variants have been linked with disease. Most variants have unknown effects. No two humans are genetically identical.
Innovations in sequencing technologies have allowed biologists to make incredible advances in understanding biological systems. As experience grows, researchers increasingly recognize that analyzing the wealth of data provided by these new sequencing platforms requires careful attention to detail for robust results. Next-generation sequencing (NGS) data, relies crucially on the accurate calling of SNPs (single nucleotide polymorphisms) and genotypes. Variant calling (identification of positions where the sequenced sample is different from the reference sequence) is a multistep process in a complex field that was significantly propelled by advances in DNA sequencing. Variant calling is essential for comparative genomics, as it yields insights into nucleotide level organismal (individual form of life) differences.