DNA IS The material inside the nucleus of cells that carries genetic information. The scientific name for DNA is deoxyribonucleic acid, the strands of life...
Right before the Ice Age there were three human-like species. One of the three was upright and bipedal but looked more like an ape. The second group resembled what we would refer to as cavemen. They had more apelike skulls and much smaller brains than we have today. The third is us. The Ice Age left a measly 2000 humans and wiped out the other two adaptations completely.
The ancestors of those who stayed-put in Africa are called the Vasikela Kung tribe. From Africa some people migrated to Asia (70,000 years ago). And the some 45,000 years ago some went towards Europe. Humans trekked from Asia across the Bering Straight and into Alaska about 25,000 years ago.
Scientists have taken DNA from the farthest reaches of humanity. They found that everyone shares some of their DNA with the Vasikela Kung. Even today you can see distinct features from all around the globe in the faces of the tribe. Their skin color is such that it can become light or dark depending on the environment.
DNA Facts:
Deoxyribonucleic Acid (DNA), genetic material of all cellular organisms and most viruses. DNA carries the information needed to direct protein synthesis and replication. Protein synthesis is the production of the proteins needed by the cell or virus for its activities and development. Replication is the process by which DNA copies itself for each descendant cell or virus, passing on the information needed for protein synthesis. In most cellular organisms, DNA is organized on chromosomes located in the nucleus of the cell.
A molecule of DNA consists of two chains, strands composed of a large number of chemical compounds, called nucleotides, linked together to form a chain. These chains are arranged like a ladder that has been twisted into the shape of a winding staircase, called a double helix. Each nucleotide consists of three units: a sugar molecule called deoxyribose, a phosphate group, and one of four different nitrogen-containing compounds called bases. The four bases are adenine (abbreviated A), guanine (G), thymine (T), and cytosine (C). The deoxyribose molecule occupies the center position in the nucleotide, flanked by a phosphate group on one side and a base on the other. The phosphate group of each nucleotide is also linked to the deoxyribose of the adjacent nucleotide in the chain. These linked deoxyribose-phosphate subunits form the parallel side rails of the ladder. The bases face inward toward each other, forming the rungs of the ladder.
The nucleotides in one DNA strand have a specific association with the corresponding nucleotides in the other DNA strand. Because of the chemical affinity of the bases, nucleotides containing adenine are always paired with nucleotides containing thymine, and nucleotides containing cytosine are always paired with nucleotides containing guanine. The complementary bases are joined to each other by weak chemical bonds called hydrogen bonds.
In 1953 American biochemist James D. Watson and British biophysicist Francis Crick published the first description of the structure of DNA. Their model proved to be so important for the understanding of protein synthesis, DNA replication, and mutation that they were awarded the 1962 Nobel Prize for physiology or medicine for their work.
• A simple list of the bases of the entire DNA in your genes—the As, Cs, Ts, and Gs—would fill about 200 New York City phone books. That’s about 3 billion letters.
• In 1985, when the Human Genome Project was first proposed, many critics thought it was absurd. At the time, the technology did not even exist to decode the sequence of a simple bacterium, much less a human being.
• While the number of base pairs—3.2 billion—on each unique person’s 23 chromosomes is quite impressive, the average human being has a mere 31,000 genes. That’s about a third fewer genes than anyone expected—and not even double the amount of genes a roundworm has. A variety of amoeba has nearly 200 times as many genes as humans do.
• Any two unrelated strangers anywhere on the planet share 99.9 percent of the same DNA. A miniscule fraction of the genome—about 3 million of its over 3 billion bases—accounts for the vast differences within the human race.
• Genomically speaking, all races are equal. In other words, you cannot tell simply by looking at someone’s DNA whether they are black or white.
• Human beings have roughly 99.1 percent of our genes in common with the chimpanzee, our closest relative on earth. The overlap between mice and humans is surprisingly close, too. We have nearly 75 percent of our genes in common.
• Single gene errors account for more than 4,000 known hereditable diseases, and the list is growing rapidly. A person’s risk for diseases from cystic fibrosis to Huntington’s now can be determined by looking at the DNA.
• The largest human gene is on the X chromosome—the dystrophin gene. Dystrophin is one of the key proteins involved in building strong muscle tissue. Boys born with a mutation in this gene end up suffering from the disorder known as Duchenne muscular dystrophy. Girls who inherit the mutation only carry the disorder, but don’t suffer from it, since they inherit an extra, healthy X chromosome from their father.
• Scientists still don’t know what more than 50 percent of genes do. Also a lot of the DNA in our cells is "junk," that is, scientists don’t know exactly what the long stretches of repetitive DNA (usually long stretches of Gs and Cs) in our cells are for.
• On human chromosome 14, a gene called TEP1 codes for a protein that forms part of a chemical known as telomerase. Some cells turn immortal if you give them enough telomerase. That sounds good, but a cell line known as cancer also needs telomerase for its own immortality project.
• For centuries folklore had it that heredity passed through the blood. Think of the terms "bad blood," "mixed blood," "royal blood," "blue blood," or "bloodline." The irony is that there is no heredity coded in your red blood whatsoever. The red blood cells are the only kind of cells in your body that don’t have DNA?because they’re the only cells in your body that don’t have nuclei.
• Eight Mysteries Solved by DNA:
o Where is Columbus Buried?
o Was Albert DeSalvo the Boston Strangler?
o Did Sam Sheppard Kill His Wife?
o Did Thomas Jefferson Father Children with His Slave, Sally Hemings?
o Did Jesse James Die in 1882, or Did He Fake His Death?
o Could the Romanovs Have Survived the Russian Revolution?
o Was Anna Anderson Really Anastasia?
o Did the Last Dauphin Escape?
FACTS about DNA Testing
A paternity test is a way to determine the biological father of a child. It is a genetic test that compares many different genetic factors in the alleged father's sample with similar genetic factors in the samples of the child and mother.
Genetic tests have a 99 percent or greater accuracy rate in identifying the probable father. If the alleged father goes to court to say he isn't the father, but experts testify that his genetic tests show that 99 percent or more of his genetic factors match the child's genetic factors, the court will find that he is the father of the child until evidence to the contrary is presented to the court.
You do not need a doctor's order to have a Paternity Test.
Samples are taken from the donor in two basic ways- by drawing a blood sample or more commonly, by using a swab, (much like a Q-tip), to scrape off a few cells from inside the mouth.
The swab is a simple, painless way to collect cells from the cheeks inside the mouth. The DNA in the cells is then analyzed to see if the alleged father's DNA matches the child's DNA.
A person acquires all of his/her DNA at the time of conception. This DNA remains the same throughout lifetime. Therefore, the accuracy of the DNA parentage test is the same throughout lifetime. Highly accurate DNA test results may be obtained before birth
Testing can be performed if one of the parties resides in another city or state.
Results can be available in as little as 48 hours.
The samples do not have to be drawn at the same time.
. Affidavits, depositions and expert witness testimonies are always available with all paternity testing.
The Drug Testing USA - GENETICA DNA Test™ for paternity is the most extensive and accurate DNA test available, with typical power of exclusion of 99.999999%.
DNA Structure
DNA is composed of strands of nucleotides joined by phosphodiester bonds between the 5'-OH of one ribose and the 3'-OH of the next.
DNA forms a double helix with these strands, running in opposite orientations with respect to the 3' and 5' hydrozxy groups.
The double helix structure is stabilized by base pairing between the nucleotides, with adenine and thymine forming two hydrogen bonds, and cytosine and guanine forming three.
DNA is a flexible molecule, and can bend, twist, and kink.
Double helix DNA can be in three forms, A, B, and Z. The most common form is B-DNA, which has about 10 bases per turn of the helix.
The B-DNA form has two grooves, a major groove and a minor groove, with the major groove being wider and deeper.
Proteins and other molecules can interact with DNA, recognizing double-stranded DNA by the phosphoribose backbone, and forming specific interactions based on the DNA sequence through access to the major and minor grooves. Most interactions occur in the major groove due to easier acess because of its size, and because there is an additional potential hydrogen bond donor from A-T residues in the major groove.
Most circular DNA is supercoiled. This structure is more compact than the relaxed form.
Negatively supercoiled DNA is partially unwound, facilitating DNA replication, RNA synthesis, and interactions with other molecules, and is the preferred form of supercoiling for most organisms.
Enzymes which affect supercoiling are topoisomerases. Topoisomers are DNA molecules which differ only in their linking number. The linking number refers to the number of helical turns the molecule possesses.
Topoisomerases break one or both strands of the DNA, and allow the molecules to relax, removing supercoils before resealing the break. The enzyme maintains the energy of the phosphodiester bond by forming an intermediate linked through a tyrosine residue, and does not require an energy input.
Supercoils are added to DNA through the activity of DNA gyrase. This enzyme uses ATP to provide energy for the reaction, breaking both strands of DNA and passing a loop through the break to introduce negative supercoils.
DNA-Modifying Enzymes
Restriction endonucleases -
Cleave at specific DNA sequences, usually palindromes, cutting both strands at precise locations about the access of symmetry.
These enzymes evolved as a bacterial defense mechanism to eliminate foreign DNA.
DNA ligase -
Catalyzes the formation of a phosphodiester bond between DNA bases, sealing breaks in the strands.
Requires an input of energy, in the form of ATP or NAD+
Forms an adenylated intermediate with the enzyme; this AMP unit is transferred to and activates the 5'-phosphate group for attack by the 3'-OH of the adjacent BASE
DNA polymerase and replication
DNA polymerases catalyze the synthesis of DNA.
The reaction involves a nucleophilic attack by the 3'-hydroxyl group on the innermost phosphorous atom of the nucleotide triphosphate. Pyrophosphate is the leaving group.
The synthesis reaction occurs in the 5'->3' direction - new bases are added at the 3' end of the growing chain.
DNA polymerase I has three activities:
5'->3' DNA synthesis
3'->5' exonuclease - used as an error corrector to check the last base of the chain to ensure accuracy.
5'->3' nuclease - used to remove bases (especially the RNA primer) ahead of synthesis occurring in the same direction.
DNA synthesis occurs at replication forks. Synthesis begins at an origin of replication and proceeds in a bidirectional manner.
DNA polymerase III is the primary enzyme for DNA replication in E. coli.
Leading the synthesis is the helicase enzyme, which unwinds the DNA strands. This introduces positive supercoils into the DNA which must be relieved by DNA gyrase. The single stranded DNA is protected by binding to a single stranded binding protein.
A primase synthesizes a short strand of RNA (about 5 nucleotides), because DNA polymerase requires a primer annealed to the template strand.
The polymerase proceeds down the helix, directly synthesizing one strand in the 5'->3' direction - the leading strand. The other strand loops around and through the polymerase, and is synthesized in short, Okazaki fragments in the 5'->3' direction - the lagging strand.
DNA polymerase I removes the RNA primers from the Okazaki fragments, replacing them with DNA.
DNA ligase seals the breaks that are left after DNA polymerase I finishes.
DNA mutations and repair
Mutations in DNA can take several forms:
Substitutions - one base is replaced for another. Can lead to a different amino acid being incorporated into the protein, or to the generation of a stop codon. There are two classes of substitutions:
Transitions - a pyrimidine replaces another pyrimidine or a purine replaces a purine
Transversions - a pyrimidine replaces a purine or a purine replaces a pyrimidine
Deletions - one or more bases is lost. Can result in frame-shift mutations.
Insertions - one or more bases is added. Can result in frame-shift mutations.
The tautomerization of adenine can result in the transition of an A-T base pair to G-C.
DNA mutagens can exert their effects in several ways:
Base analogs can be incorporated into DNA, these may form tautomers more readily and lead to substitutions. Ex: 5-bromouracil and 2-aminopurine.
Agents can chemically modify the DNA bases, leading to substitutions during replication due to changes in base-pairing.
Agents can intercalate into DNA, causing deletions and insertions during replication.
UV light can generate pyrimidine dimers - pyrimidine bases which are covalently linked.
Most organisms have one or more repair mechanisms to remove pyrimidine dimers. A common method uses an excinuclease to remove a fragment containing the defect, filling the gap with DNA polymerase, and sealing the break with DNA ligase.
To facilitate repair of mistakes made during replication, parental DNA must be distinguished from the newly synthesized DNA. This can be accomplished by methylating adenine residues in GATC sequences.
One reason that uracil is not used in DNA may be because uracil is the product of a deamination of cytosine. This would result in a substitution every time this reaction occurred. To prevent this, uracil in DNA is removed by uracil-DNA glycosidase and the gap is filled.
Defects in DNA repair can lead to the development of cancers such as Xeroderma pigmentosum and hereditary nonpolyposis colorectal cancer. The former can be caused by a defect in the removal of pyrimidine dimers, while the latter is a defect in mismatch repair.
Some DNA mutagens can be identified on the basis of their ability to cause revertants of His- Salmonella mutants. When plated on medium lacking histidine, these revertants will be able to grow
FOR EXAMPLE the evolution of the dog, showing its decedents over millions of years. Darwin suggested that wolves, coyotes, and jackals, may all have played a role, producing a complex dog ancestry that would be impossible to unravel.
Based on anatomy, most biologists have put their money on the wolf, but until recently there was little hard evidence, just lots of opinions.
The issue was finally settled in 1997 by an international team of scientists to sort out the evolutionary the family dog, they used techniques of molecular biology to compare the genes of dogs with those of wolves, coyotes and jackals.
Blood, tissue, hair from 140 dogs, 67 breeds, 162 wolves from North America, Europe, Asia, and Arabia. From each sample they extracted DNA from tiny organelles within cells called mitochondria.
While the chromosome DNA of an animal cell derives from both parents, the mitochondrial DNA comes entirely from the mother. Mitochondrial DNA will show a line of descent, female to female to female. As changes called mutations occur due to copying mistakes or DNA damage, the mitochondrial DNA of two diverging lines becomes more and more different.
Ancestors can be clearly identified when you are studying mitochondrial DNA, because clusters of mutations are not shuffled into new combinations like the genes on chromosomes are. They remain together as a particular sequence, a signature of that line of descent.
When they looked at canine mitochondrial DNA samples, they found that wolves and coyotes differ by about 6% in their mitochondrial DNA, while wolves and dogs differ by only 1%. Already it looked like the wolf was the ancestor of our pet dogs.
They then focused their attention on one small portion of the mitochondrial DNA called the control region, because it was known to vary a lot among mammals. Among the 67 breeds of dogs, they tested, they found a total of 26 different sequences in the control region, each differing from the others at one or a few sites.
No one breed had a characteristic sequence, the breeds of dogs share a common pool of genetic diversity. Wolves had 27 different sequences in the control region, none of them exactly the same as any dog sequence, but all very similar to the dog sequences, differing from them at most at 12 sites along the DNA, and usually fewer.
Coyote and jackal were a lot more different from dogs than wolves were. Every coyote and jackal sequence differed from any dog sequence by at least 20 sites, and many by far more.
Using statistical methods to compare the relative similarity of the sequences, they found that all the dog sequences fell into four distinct groups. The largest, containing 19 of the 26 sequences and representing 3/4 of modern dogs, resulted from a single female wolf lineage.
Conclusion
The domesticated dog descended from the wolf :)
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