#5 The Evolving Science of Evolution
Posted on February 23, 2019 by Diana Roberts
Mitochondrial Eve (“mt-MRCA”) is the matrilineal most recent common ancestor of all currently living humans. Estimate on this maternal tracking is about 150,000 years ago, consistent with a date later than the speciation of Homo sapiens but earlier than the recent Out-of-Africa dispersal. The name “Mitochondrial Eve” alludes to biblical “Eve.” This has led to repeated misrepresentations or misconceptions in journalistic accounts on the topic. Mt-MRCA is neither fixed in time, nor does it refer to “first woman,” nor to the only female of her time, nor the first member of a “new species.”
Mitochondrial DNA: Mitochondria are the 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 (the cytoplasm). Although most DNA is packaged in chromosomes within the nucleus, mitochondria also have a small amount of their own DNA. The genetic material is known as mitochondrial DNA or mtDNA. In humans, mitochondrial DNA spans about 16,500 DNA building blocks (base pairs), representing a small fraction of the total DNA in cells.
Mitochondrial data contains 37 genes, all of which are essential for normal mitochondrial function. Thirteen of these genes provide instructions for making enzymes involved in oxidative phosphorylation. Oxidative phosphorylation is a process that uses oxygen and simple sugars to create adenosine triphosphate (ATP), the cell’s main source. The remaining genes provide instructions for making molecules called transfer RNA and ribosomal RNA, which are chemical cousins of DNA. These types of RNA help assemble protein building blocks (amino acids) into functioning proteins.
Chromosomes: In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes. Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure. Chromosomes are not visible in the cell’s nucleus – not even under a microscope – when the cell is not dividing. However, the DNA that makes up chromosomes become more tightly packed during cell division and is then visible under a microscope. Each chromosome has a constriction point called the centromere, which divides the chromosome into two sections, or “arms.” The short arm of the chromosome is labeled the “p arm.” The long arm of the chromosome is labeled the “q arm.” The location of the centromere on each chromosome gives the chromosome its characteristic shape, and can be used to describe specific genes.
Genome: A genome is an organism’s complete set of DNA, including all of its genes. Each genome contains all of the information needed to build and maintain that organism. In humans, a copy of the entire genome – more than 3 billion DNA base pairs – is contained in all cells that have a nucleus.
Geneticist, David Reich, has just come out with an astounding book Ancient DNA and the New Science of the Human Past, who we are and how we got here (Amazon). In Twogaa’s next posting, we shall share some of his findings and the progression of evolution study. The beauty of science is that it does not stand still. Once it reaches a conclusion through the scientific method it is then searching for the next question that conclusion brought forth.