What is a Gene?
Let's Stay Simple
Under a heading of 'How did the DNA code originate', Creation Ministries International asks, 'The code is a sophisticated language system with letters and words where the meaning of the words is unrelated to the chemical properties of the letters - just as the information on this page is not a product of the chemical properties of the ink (or pixels on a screen). What other coding system has existed without intelligent design? How did the DNA coding system arise without it being created'?
A gene is the basic physical and functional unit of heredity. Genes are made up of DNA (deoxyribose nucleic acid) and act as instructions to determine the exact composition of each molecule of protein.
Proteins can be functional or structural components of the body. Examples of functional proteins are enzymes, protein hormones and immune proteins. Enzymes allow the numerous chemical reactions of the body to proceed; insulin and growth hormones are proteins that control development and immune protein molecules protect the body from infections and damage. Examples of structural proteins are muscles, ligaments, tissues and cell membrane components.
In other words, no living cell can exist without genes and without the very complex mechanisms that actually produce proteins from the instructions coded on those very same genes. The notion of arriving at a living cell that can reproduce itself from a mix of chemicals in a pool of water, no matter how complex, is total fantasy and a delusion of rebellious man who does not wish to believe in a Creator!
In humans, genes vary in size from a few hundred DNA bases (comprised of only a four letter genetic code of A, T, C and G) to more than 2 million bases. The Human Genome Project has estimated that humans have between 20,000 and 25,000 genes. Francis S. Collins who made fundamental discoveries at the cutting edge of the study of DNA himself, led the Human Genome Project and in 2006 published the New York Times best seller, 'The Language of God: A Scientist Presents Evidence for Belief'. No one can deny that DNA is the code of life. It not only harbours genes within itself but also in mysterious way has the ability to pass on the timing of developmental events hidden in its code. Predetermined developmental processes, circadian rhythms (biological clocks) and flowering seasons of plants are examples of that. Some flowering plants can tell the difference between short-days and long-days with an accuracy of 20 minutes or less as has been experimentally proven in environmentally controlled growth cabinets.
Thus mouse DNA limits their life span to about 1 year while turtles have a life span of 80-150 years. The same is true of plants. Wheat has a genetically determined life span of one season while the bristle-cone pine can live up to 6000 years. Some plants are genetically predetermined to die as soon as they flower and set seed. Every gardener would know the difference between annual plants, biannual plants and perennial plants. Who wrote these precise programs onto the DNA we may ask?
Every person has two copies of each gene, one inherited from each parent. Most genes are the same in all people, but a small number of genes (less than 1 percent of the total) are slightly different between people such as genes determining blood grouping. Alleles are forms of the same gene with small differences in their sequence of DNA bases. These small differences contribute to each person’s uniquely different physical features such as eye colour, fingerprints, etc.
Each gene exists as a small segment on long strings of DNA that contain many other genes much like the words of the prayer on the rosary chain of Catholics. All living cells, except for blood platelets, have their own complete set of genes. Depending on the cell's location in the human body each cell has to 'know' which set of genes to choose (to express) for making proteins and which selection of genes not to express. Thus cells that make heart tissue must not express genes for making an eyeball. So-called Master Genes in cells 'call the shots' just like military drill commanders do for a complex manoeuver on the parade ground.
Genes are packaged within chromosomes. Each chromosome is a very long string of supercoiled DNA containing many genes and is wrapped around protein complexes called nucleosomes, which consist of proteins called histones. Their bulky structures allow us to see them under the microscope, but only when cells are dividing. In other words, chromosomes are complex structures that allow the DNA to be multiplied into duplicate copies as cells divide.
This form of the DNA only becomes visible under the microscope just prior to cell division where each new cell receives its full complement of genes. Otherwise the DNA is invisible under the microscope except if specially prepared for the electron microscope at very high magnifications. In school biology classes thin onion peels are used to demonstrate chromosomes because they always have a number of cells undergoing division.
The next illustration below shows a stretch of DNA 23 bases or letters long (A, C, G or T). Two copies are shown because we inherit one copy of DNA from our father and one copy from our mother. They are virtually identical. Thus, we have two copies (each called an allele) of every gene in every one of our cells. That’s a lot of DNA to pack into every cell. This redundancy is also a safety measure in case one of the copies develops an error. That would lead to a genetic disorder. In other words, the letters may have become disordered.
We inherit our DNA as a mix of genes from our forefathers going all the way back to Adam and Eve. However, we also have a few genes in our mitochondrial DNA ( a tiny organ or organelle in each of our cells responsible for energy production). Mitochondria have been maternally inherited from Eve. (See article under REPRODUCTION). That is why palaeontologists are so interested in finding old bones from which they might be able to isolate ancient mitochondrial DNA going faithfully in its identity all the way back to Eve.
DNA CODES FOR MORE THAN JUST PROTEINS
Since the same DNA is in every cell, with a few exceptions, it means that every cell carries the entire DNA manual for making an adult body. Included, somehow is the determined developmental sequence and timing of processes as we grow from a single cell to an adult. During normal cell division (mitosis) each new cell receives the same pairs of genes that were in the original cell. Genes come in pairs, so that every gene has a duplicate form.
All this genetic material has to be specially packaged so it can fit into the nucleus of living cells. In humans 2.1 metres of DNA is compressed by super-coiling into 46 bits or chromosomes and then stored in the nucleus of each human cell.
The illustrations below show chromosomes duplicated during division and the location of certain genes on one pair of allelic X-chromosomes - i.e. one from the mother and one from the father (technically known as homologous chromosomes). Humans have 23 pairs of chromosomes, one pair being the sex determining pair of X-Y chromosomes.
The images show details of an X-chromosome in the process of division containing one long piece of supercoiled DNA, which contains hundreds or thousands of genes. How would the cell find a particular gene it needs in all this mess? Yet the apparent confusion is not chaotic because signals and molecular tags direct the genetic machinery to locations where it is needed to untangle the DNA for RNA production and protein expression. The detailed study of genetics is fascinating.
Extensive controlled coiling of DNA is crucial to form chromosomes in their visible shape for cell division, but so will be uncoiling at various phases of the cell cycle.
During DNA duplication, while the cell is undergoing division, special proof-reading proteins (enzymes) edit the DNA correcting perceived mistakes! How amazing is that?
How other enzymes, specialised complex proteins, can find the appropriate gene on the DNA to decode the required genes at any particular time, in all that tangled mess of about 24,000 genes, is still to be discovered. I have no problem if the mechanisms are eventually discovered. It’s simply a matter of discovering what God had designed and so ordained.
Sex is determined at conception by the pair of X and Y sex chromosomes. Males have XY and females have an XX pair of chromosomes. Anyone who has a Y chromosome is male. Note that, because females are XX, all egg cells will be X. Males will carry two types of sperm, a mix of X and Y. If an X-containing sperm cell fertilizes the egg cell then the embryo becomes female (XX). Thus males determine the sex of the resulting embryo.
In appearance and size the Y sex chromosome is much smaller and has far fewer genes than an X sex chromosome and looks like a small ‘v’ with a tiny tail when dividing cells are stained with colour. However, its basic form is little different to X chromosomes.
The two halves of each chromosome, whether X or Y, will separate along their length from where they are joined. Thus in shape, an X will split into two I-shaped halves and each 'I' will end up in one of the two new cells. In normal cell division each cell will therefore end up with an identical DNA manual on how to proceed further.
Soon after cell division the chromosomes will be loosened from their compact configuration and disappear from view because they will become very thin and float freely within the cell nucleus. This figure shows the 22 pairs of homologous (complementary) human chromosomes stained, artificially lined up for photography into pairs and shown separately in a box, are the two sex-determining chromosomes, XY in this example. Thus, in all we have 46 chromosomes per normal body cell. They float around in the nucleus unpaired. By staining dividing cells technologists can work out which chromosome is which is which. Scientists have been able to locate the specific genes on each chromosome. The yellow stripes shown on chromosome 7 indicate regions of the chromosome where genes important to the researcher, who created this diagram, are located.
"…..the human Y chromosome, at the same time, plays a central role in human biology. The presence or absence of this chromosome determines gonadal sex. Thus, mammalian embryos with a Y chromosome develop testes, while those without it develop ovaries. What is responsible for the male phenotype is the testis-determining SRY gene …."
Lluís Quintana-Murci and Marc Fellous, Journal Biomedical Biotechnology. 2001; 1(1): 18–24. (SRY is an abbreviation used in literature for the testis-determining master gene).
In the diagram shown below the Y sex chromosome is illustrated banana shaped. Y chromosomes were not named necessarily after shape but because Y followed X in the alphabet, X originally was so named for ‘unknown’. The illustration shows how chromosomes from parents are allotted to their children. In the sex cells (sperm or egg), which are different from normal body cells because they don't contain chromosome pairs, the sperm cells contain either an X or a Y of the sex chromosome plus the other 22 chromosomes. In egg cells, because women have no Y chromosomes, the sex chromosome is an X together with the other 22 chromosomes (known as autosomal or body chromosomes). Thus males contribute either an X or a Y, but women can only contribute an X sex chromosome.
Most of the genes in chromosomes are for functions such as body housekeeping and maintaining metabolism. That is why the DNA profiles of apes are close to humans. It’s the differences that count not the similarities. So, let’s not be fooled that we are descended from apes just because the DNA sequences have high similarities between humans and apes. God wanted us to enjoy and appreciate monkeys and apes, and laugh at their antics which remind us of ourselves. God has humour.
Consider the DNA sequence similarity of 96 to 98.8 % between humans and chimpanzees, depending on how sequence similarity is reckoned. That makes us very close indeed you would say. Yet our sequence similarity with a cat is 90%. We don’t look anything like a cat and we certainly don’t look like bananas that have a 50% sequence similarity with us. My point is that it’s the difference in a small number of genes that make us so different. Sequence similarity has little to say about ancestry by Darwinian descent.
This information was taken from a rather neat blog by an evolutionist: Human DNA similarities to chimps and bananas, what does it mean? Check it out by clicking on the site:
A genetic disorder arises when a piece of DNA in a gene is damaged. In case of genetic disorders it depends on which particular chromosome the DNA of a gene is damaged. In the illustration above follow the red star to see how a mutation is carried through the generations. The green star indicates a genetic error on the Y chromosome of a male. Since this can only be inherited by boys the green star represents a sex-linked genetic disorder. In other words only males will be carriers and exhibit the disease. The red star mutation is evidently not sex linked.
For specific examples on cystic fibrosis and haemophilia see the article on GENETIC MUTATIONS. It’s almost that simple, but not quite. Genetic disorders arise from a faulty gene where the protein produced may not do its specific task in the body, or it may have lost its ability to be regulated because of structural and amino acid changes within itself.
Congenital genetic disorders arise when a mutation occurs during pregnancy, such as being exposed to radiation or mothers having taken the drug thalidomide for pain relief, when children were born with deformed limbs. Measles during pregnancy can cause serious congenital problems in the foetus because the virus interferes with developmental processes within the embryo. The chromosomes of the foetus may or may not be rearranged according to the severity of the individual case. It is primarily the expression of the genes in the DNA that is being affected.
The beauty of creation is that all of us become unique individuals because of recombination and rearrangement of some parts of our chromosomes during sexual recombination (this is beyond our scope here). Our uniqueness can most frequently be picked up by our DNA profiles following analysis of our genome or by simple methods, such as fingerprinting, which is determined by the unique DNA code each of us carry. Thus, mankind is not the product of cloning and therefore we are not a bunch of obedient robots. However, even courts must have more associated evidence because there is a possibility that some have near identical finger prints and DNA profiles.
Plants, on the other hand, can either be cloned or sexually reproduced. In sexual reproduction by cross-pollination, each subsequent seed becomes a unique individual. Large acreage crops such as wheat have had their inherent variability bred out over the centuries. Imagine if every single wheat plant had a different height and matured under different conditions. How would one ever harvest a crop on a large scale?
However, many plants reproduce their cells entirely by non-sexual cell reproduction (Mitosis). This occurs through budding or by tissue culture from individual cells, or, more generally, by taking cuttings and grafting onto a root cutting. The newly growing plant will be identical to the parent plant from which the cutting (scion) was taken. Hence the practice of taking a branch from a vine, whose grapes are desirable, and grafting it onto a hardy, disease-resistant root system (the stock). Highly desirable seedless grapes also have to be cloned, if identically the same is desired, because there are no seeds to plant. Seedless oranges were ‘invented’ when an abnormal branch on a tree was found to bear oranges without seed (its reproductive system went wrong). Seedless orange trees were perpetuated by cloning individual cuttings of the branch through grafting onto many root stocks and producing many trees.