Back to the Basics

Before discussing how families can be traced through genetic testing, first one must understand the basics of how genetics work. As you may remember from your high school biology courses, part of your genome is inherited from your mother and part from your father. The reality is a little more complicated than that.

To start, it all goes back to meiosis. Meiosis is the process by which gametes and zygotes are formed. These are the initial cells which will be fertilized to grow into new living beings.

Meiosis occurs in eight stages with Prophase I being the important stage for our discussion. During Prophase I, the chromosomes condense and are able to exchange genetic material. Meiosis then continues until Telophase II and cytokinesis. The end result of meiosis is is four daughter cells each with unique genetic material and half the number of chromosomes. When fertilization occurs, two of these daughter cells fuse to from the zygote which eventually becomes a fetus.

Assumptions versus Reality

So siblings should then share roughly 100% of their genetics with each other right? No.

Remember that exchange of genetic material in Prophase I of meiosis, that exchange happens differently each time that meiosis occurs. Due to that fact, full-blooded siblings share anywhere from 38-61% of their DNA with each other and 50% with the parent. That percentage decreases the further your family tree spreads.

Then how can genetics and DNA be used to trace your lineage through the centuries? The answer comes in the form of mitochondrial DNA.

What is mitochondrial DNA?

Mitochondrial DNA is DNA found in the mitochondria of cell. When the gametes are being formed through meiosis, the organelles (including the mitochondria) are also replicated. Unlike the chromosomes, however, the mitochondria is copied without that genetic exchange. This means that the mitochondria is inherited without change from the parent cell to the daughter cells minus potential mutations.

This mitochondrial DNA is then inherited directly from the mother to the child without change assuming no mutations arise during replication. Since this DNA is inherited directly from the mother to the child, your genetic lineage can then be traced through the centuries.

So while the DNA you inherit from your father is important for providing genetic variably and making you you, the DNA you inherited from your mother through her mitochondria allows you to trace your ancestry from your mother to her mother and so forth.

~~ Emily H. – MS Biochemistry (BS Cellular and Molecular Biology and Biochemistry) Return to home

The age of the Appalachian Mountain range varies due to different parts of the range forming at different times. The oldest part of the Appalachian Mountain range formed before the Cambrian roughly 1-1.2 billion years ago. While the youngest parts of the range finished forming during the Jurassic period with the opening of the Atlantic Ocean roughly 144 million years ago. It is those pre-Cambrian ranges we will be focusing on for this discussion.

Formation of Mountains and Supercontinents

Before discussing how the Appalachian Mountains formed, we need to discuss how mountain ranges form in general. As you may remember from geology classes, the continents are not just floating around the ocean. They are on layers of rocks called tectonic plates. These tectonic plates rest on top of a partially molten layer of rock and are able to move due to the heat from this molten layer. As these tectonic plates slide against each other, they can cause earthquakes; however, when these plates collide with each other, they can form mountain ranges. This occurs when two continental plates collide, and the land in between the two plates is pushed upwards creating mountains.

The first continental collisions which formed parts of the Appalachian Mountains occurred with the formation of the supercontinent, Rodinia. During part of the formation of this supercontinent roughly 1 billion years ago, the continents of Laurentia (containing land that would become North America) and another continent, potentially Amazonia (part of what would become South American) collided. This collision formed parts of the Appalachian Mountains through the Grenville orogeny [1]. The parts of the Appalachian Mountain range formed by this collision were as follows: “the northern Long Range of Newfoundland, The Green Mountains of Vermont, The Berkshire Highlands of Massachusetts, the Hudson Highlands of New York and their extension across New Jersey into the Reading Hills of Pennsylvania, the Mine Ridge-Honeybrook uplift of Pennsylvania, and the South Mountain-Blue Ridge uplift extending from Maryland across Virginia into North Carolina and Tennessee.” [2] The supercontinent of Rodinia would eventually break up through the continental rifting which separated the supercontinent into at least two continents: Laurentia and Gondwana [3] by the Cambrian period, although there is still debate about how exactly Rodinia broke up and what exactly happened next.

Older than Bones?

Why then claim that the formation of the earliest parts of the Appalachian Mountains are older than bones? That is because the earliest signs of multicellular animals paleoarchaeologists have found are from small sea creatures known as the Ediacaran biota. This period of time known as the Ediacaran period began 635 million years ago and lasted until the beginning of the next period of time 541 million years ago: the Cambrian period. The Cambrian period is most well-known for the Cambrian Explosion where life evolved and diversified into many different forms which had never been seen before. This is also the period in which calcium carbonate shells first evolved [4]. The advent of a calcium carbonate shell paved the way for animals to develop exoskeletons and eventually bones. This process all started around 541-500 million years ago well after the formation and breakup of Rodinia.

So are the Appalachian mountains older than bones? The parts of the mountain range that formed a billion years ago when Rodinia formed are certainly older than bones. The story of the formation of the Appalachian Mountain range does not end with the breakup of Rodinia. There would be a few more major collisions in her future.

First, Laurentia would collide with the continents of Avalonia and Baltica to form Laurussia during the Silurian Period [5]. The continents of Laurussia and Gondwana then slowly began their journey towards each other once again eventually forming Pangaea. This collision during the late Carboniferous period would cause the final formation of the Appalachian Mountains known as part of the Central Pangaean Mountains. Finally with the break-up of Pangaea during the Triassic period, the Appalachian Mountains stayed on the North American continent and over millions of years became the mountains we know today.

1. Faill, R.T. (1997) A geologic history of the north-central Appalachians; part 1, orogenesis from the Mesoproterozoic through the taconic orogeny: American Journal of Science, v. 297, no. 6, p. 551–619, doi: 10.2475/ajs.297.6.551.
2. Rodgers, J. (1967) Chronology of Tectonic Movements in the Appalachian Region of Eastern North America: American Journal of Science, v. 265, p. 408-427.
3. Z.X Li, S.V. Bogdanova, A.S. Collins, A. Davidson, B. De Waele, R.E. Ernst,I.C.W. Fitzsimons, R.A. Fuck, D.P Gladkochub, J. Jacobs, K.E. Karlstrom, S. Lu, L.M. Natapov, V. Pease, S.A. Pisarevsky, K. Thrane, V. Vernikovsky (2008) Assembly, configuration, and break-up history of Rodinia: A synthesis, Precambrian Research, v. 160, no. 1-2, pg. 179-210. doi: 10.1016/j.precamres.2007.04.021
4. Darja Obradovic Wanger & Per Aspenberg (2011) Where did bone come from?, Acta Orthopaedica, 82:4, 393-398, doi: 10.3109/17453674.2011.588861
5. W. S. McKerrow, C. Mac Niocaill, P. E. Ahlberg, G. Clayton, C.J Cleal, and R.M.C. Eagar (2000). The Late Palaeozoic relations between Gondwana and Laurussia, Geological Society, v. 179, p, 9-20. doi: 10.1144/GSL.SP.2000.179.01.03

~~ Emily H. – MS Biochemistry (BS Cellular and Molecular Biology and Biochemistry) Return to home