The Common Ancestry Thread

by cantleave 271 Replies latest members adult

• 

  cantleave

  Jgnat the Genographic project uses mitochobdrial DNA which is passed only through the egg. Thus, it is not a combination of male and female genes. It is a haploid gene - meaning that it has only one dose of chromosomes. The haploid mitochondrial DNA shows only the female lineage of a person. Diploid genes are two sets of combined chromosomes, the female set coming from the egg, the male chromosomes from the sperm.

  Mitochondrial DNA is categorized into several types and groups termed haplotypes and haplogroups. That is, there are variations in the genetic code of mitochondria that fit into clusters. These clusters can trace lineage far back into time.There are 39 different and distinct mitochondrial DNA groups into which all humans fit and there are variations on these types.

  While mito chondrial DNA analysis is not only easier than other forms of genetic testing, it has a further advantage. All DNA mutates over time. But mitichodrial DNA has a fairly steady rate of mutation that permits a reasonably accurate estimate of exactly when a particular group of people migrated from their primary group.

  Thus, two important factors can be determined through analysis of mitochondrial DNA. First, a living person (or the mitochondrial DNA from the remains of a deceased person) can be tested to determine the specific racial group from which the Individual came.Secondly, the approximate time when that Individual's ancestors migrated from their primary racial group can be determined.

  One way to view mitochondrial DNA testing is that it may be able to provide a racial family tree extending back to the beginning of humanity. The current idea in mitochondrial DNA analysis is that ancestry on the female side can eventually be traced back to a common ancestor (sometimes referred to the "Genetic Eve"). The 39 types of mitochondrial DNA were presumably derived from this ancestor.So you can imagine the implications of that!
• 

  cofty

  Another piece of genetic evidence for the evolution of humans is the amount of junk in our genome.

  Here is how our DNA breaks down...

  1.5% codes for proteins

  4% is regulatory DNA

  10% is structural DNA - centromeres and telomers which compensate for a substandard copying mechanism

  21% are LINEs Long Interspersed Nuclear Elements (parasitic)

  13% are SINEs Short Interspersed Nuclear Elements (parasitic)

  8% are ERVs Endogenous RetroViruses (parasitic)

  3% are DNA Transposons (jumping genes, also parasitic)

  That gives us 45% of our genome that we know for certain is parasitic - it is JUNK. The remaining 40% is currently unknown.

  There is no mechanism to remove junk DNA from our genome although one species of fish, the Fugu sesm to have learned how. It has the leanest meanest genome we know of, just 390 mb (mega bases) compared to our 3300 mb. It appears to have learned the trick of removing junk DNA from its genome.

  By contrast t he onion Alium altyncolicum has double the DNA we do and a very similar species of onion Alium ursinum has TEN times as much.

  Ther is even a species of rice that has a bigger genome than humans - of course it hasn't sequenced its genome yet.
• 

  cantleave

  Cofty, thank you for posting that clarification. The term "junk" DNA musn't get confused with all non-coding DNA since some sequences s of non-coding DNA do have important biological functions, including the transcriptional and translational regulation of protein-coding sequences.
• 

  cantleave

  Where are our evolutionary skeptics??????
• 

  PSacramento

  Where are our evolutionary skeptics??????

  Do you really want the drama?

  I think that IF you want a viable discussion that, maybe debating what is the prime mover of evolution may be interesting.

  Or not.

  Personally I find environmental factors are probably THE main influence in evolution ( discounting the theistic option of course).
• 

  cofty

  When genes no longer function they are not removed from the genome but remain as ancient relics telling the story of our family tree.
  
  An excellent illustration I read recently compared the journey through our genome to walking through a neighbourhood. Some homes are still occupied and well cared for; others have long since been abandoned and are in various states of disrepair. So it is with obsolete genes, depending on how long ago they ceased to function they display various levels of mutation.
  
  What then of our more distant ancestors, is there still evidence in our, “how to build a human” book for our much more ancient reptilian heritage? One of the definitive differences between mammals and reptiles is the way we nurture our offspring. While reptiles lay eggs, mammals, with a couple of remarkable exceptions, gestate their young internally via the placenta.
  
  I was astonished to discover that we still have the instructions in our genes for making eggs, in fact the very same genes that are still active in fish, amphibians, reptiles, insects and birds to this day!
  
  The nutritious content of eggs is a protein called vitellogenin. Amazingly all mammals including humans carry the three genes that produce this main ingredient in egg yoke.
  
  All three genes (VIT1,2 and 3) are long since disabled by mutations but there they are, in every cell in your body, a paragraph in your instruction manual that has not been read for millions of years until 3 geneticists at the University of Lausanne in Switzerland identified them just a few years ago.
  
  Let me say that again, it makes my head spin, the instructions for making egg yoke is contained in every mammal on the planet including you and me! These ancient pseudogenes testify to a common origin with all our egg-laying cousins.

  All three genes have been disabled by mutations in the distant past. Now they resemble an old broken typewriter collecting dust in the storeroom of a modern office; physical evidence of previous times.
  
  Even though the ability to make vitallogenin has long been lost, the human embryo still prepares for the nutrition that never comes. In the early weeks of pregnancy a large egg sack develops, attached to the abdomen. It is completely useless and filled with fluid. By the end of the second month it detaches.
  
  In case you have any doubts here is a pic; not taken from baby's best angle - the embryonic head is at the top of the picture, the empty yoke sac is the main balloon shape in the centre.

  
• 

  cantleave

  Psac,

  That is an interesting question. I agree with you entirely. Natural selection is very much moulded by environmental factors, and where we have observed evolution in progress, it has been where populations have become isolated and had to deal with different envorimental factors.

  TBH I don't want an adversarial thread but it would be great if one of the critics read this and commented on evidence they keep telling us doesn't exist.
• 

  cofty

  There is one exception to the rule that all mammals have lost useful copies of the genes for making vitallogenin. The amazing duck-billed platypus, like us humans, has copies of the same 3 genes. But unlike us one copy of the gene still works and almost uniquely to the world of mammals it's an egg layer.
  
  One other interesting thing about the platypus; it has no stomach, just a slight swelling of the esophagus. It lacks the glands for producing digestive enzymes, perhaps it's insect diet no longer needs the usual digestive machinery. What it does have is two genes for making those enzymes, both disabled by mutations.
  
  There is almost no end to the evidence from pseudo-genes that testify to the previous forms of living things.
• 

  cofty

  double post
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  cantleave

  Cofty, that is a good point. In fact embryoligy provides a great deal of evidence about our evolutionary history.