MECHANISMS OF GENETIC VARIATIONS

Allele

A DNA coding that occupies a specific place on a chromosome. Alleles hold genetic information such as the color of flower petals.

Genotype

The inheritable information carried in the cells of all living organisms. This stored information is used as a "blueprint" for building and maintaining the organism

Phenotype

The physical attributes of an organism. They are caused by both the organism’s genotype and its environment.

Latent

Present and capable of becoming active, but not yet visible or active.

Patent

Visible and active.

Morphology

What an organism looks like and what it is made of, also known as the form and structure of an organism.

Adaptive Radiation

The rapid diversification of a species to suit many different environments.

Physiology

The functions in living things, or the scientific study of those functions.

Preadaptation

When a creature uses a feature of their anatomy for a purpose seemingly unrelated to its original task.

Built-in Variation in the Gene Pool

For most character traits present in organisms, more than one allele exists. The different genes must have come about by chance alone, because we are dealing with genotype. The genotype of an organism includes both latent and patent genes. Only genes that have been activated are expressed in the phenotype. A new gene must first be expressed before natural selection comes into play.

As far as alleles are concerned, expression is governed by a complex system of dominance versus recessiveness. Furthermore, the frequency of genetic expression can also alter the phenotype. For example, the gene coding for growth hormone can influence the size of the organism. Variation in size does thus not necessarily require new genes, just differential expression of the same genes. An example of built-in variation in the gene pool can be seen in the differences between breeds of dogs. As to how the genes responsible for the variation came in to existence, chance or design are the only options given, since we are dealing with genotype.

By selecting from the built-in natural variation of the gene pool, various breeds of dogs and domestic cattle were produced. Great changes in physiology and morphology are involved, and evolution is here certainly excluded. Differences in dogs are greater than the differences in genera of the Canidae family.

Genetic expression is also influenced, so as to bring about differences in structural expression by the genes in terms of size. Differential hormonal modulation in response to environmental stimuli can alter the time and magnitude of response, effectively producing reproductively isolated communities which would be regarded as different species by evolutionists, but are in effect merely extremes of genetic expression within an existing gene pool. The vast numbers of latent genes would then be accounted for.

Evolutionists recognize that changes in genotype frequencies do occur to produce changes in gene distribution. They, however, explain most changes as resulting from chance mutations, and this is not tenable.

Even evolutionists admit that preadaptation must have played a major role in enabling organisms to survive environmental changes. Preadaptation, however, requires preexisting genes capable of responding to environmental stimuli—precisely what creationists claim. Where did these fully expressional genes come from? 

Homologous

Similarity in structure between parts of different organisms, such as the similarity between a human hand and a bat wing.

Genotype

The inheritable information carried in the cells of all living organisms. This stored information is used as a "blueprint" for building and maintaining the organism

Phenotype

The physical attributes of an organism. They are caused by both the organism’s genotype and its environment.

Genome

A full set of chromosomes. A regular cell contains two full genomes.

Ligase

An enzyme that joins two larger molecules together with a chemical bond.

DNA

Deoxyribonucleic acid (DNA) is a molecule that stores genetic make up, or code. All living things have DNA.

Chiasma

The point where two chromatids are interwoven in a cell.

Chromatid

One of the two identical halves of a replicated chromosome.

Nucleotide

Molecules that join together to make up the structure of DNA and RNA.

Reproductive Exchange

Through sexual reproduction, genetic material is exchanged. This induces genetic recombination. The significance of this is obvious: the exchange of material increases the variation. This holds particular advantages to populations and is considered by evolutionists to be an innovation that greatly enhances the evolutionary process.

We know what sexual reproduction achieves. It increases the variation. However, increased variation in the genotype is of no value until it is expressed in the phenotype. The new varieties must be expressed in the offspring before natural selection can feast on this increased variation. The process that brings about the variation (sexual reproduction) is not subject to selection, only the result thereof (the increased variation in the offspring) is subject to selection.

The exchange of gametes requires a modified form of cell division which is the process of meiosis. During meiosis, the number of chromosomes is halved, resulting in the gametes having half the chromosomes. Sexual fusion of two gametes then restores the number of chromosomes. Variation in the genome is greatly increased by two processes occurring during meiosis: independent assortment and crossing over. Both these processes are extremely complex, but in themselves are not subject to selection. They rearrange the genetic material, resulting in new combinations of the material. As this reshuffling occurs at the level of the genotype, it is not subject to natural selection until the new combinations have been expressed in the phenotype. 

i) Independent Assortment

Independent assortment is achieved when chromosomes line up in homologous pairs and move independently to the one pole or the other. The process is governed by complex enzyme systems which in turn must also have come about by chance. The possible variation that can be achieved by independent assortment depends on the number of chromosomes present. In humans, there are 46 chromosomes, which would arrange themselves in 23 homologous pairs. There are thus 80 trillion possible variations.

ii) Crossing Over

Crossing Over is an awe-inspiring process. When homologous chromosomes are lined up during meiosis, they can, in a very precise way, exchange genetic material. There are five steps in achieving this:

a) Enzymes open the double helix of DNA in the aligned chromosomes to permit intermolecular base pairing.

b) One strand of each helix is cut at equivalent positions.

c) The enzyme ligase joins them to form a half-chromatid chiasma (because only one strand of each chromatid cross over), resulting in a cross-shaped molecule.

d) The cross-shaped molecule is cut in half by an enzyme, leaving a break in one strand of each recombinant.

e) The break is sealed by ligase.

The process has to be extremely precise. If even one nucleotide is transferred incorrectly, the genetic message becomes useless.

Somehow the genetic material from one parental chromosome and the genetic material from the other parental chromosome are cut up and pasted together during each meiosis, and this is done with complete reciprocity. In other words, neither chromosome gains or loses any genes in the process. In fact, it is probably correct to say that neither chromosome gains or loses even one nucleotide in the exchange.

Plasmid

A DNA molecule that is separate from the chromosomal DNA, and can replicate without the chromosomal DNA.

Genome

A full set of chromosomes. A regular cell contains two full genomes.

DNA

Deoxyribonucleic acid (DNA) is a molecule that stores genetic makeup, or code. All living things have DNA.

Nucleotide

Molecules that join together to make up the structure of DNA and RNA.

Transposons

Sequences of DNA that can move around to different positions within the genome of a single cell. In the process, they can cause mutations and change the amount of DNA in the genome.

Transposons

Chunks of DNA that can move around within a genome.

Transposable Elements

Transposable elements are sometimes called "jumping genes." They consist of segments of DNA that can move from one position on a chromosome to another. In 1951, Nobel prize-winning Dr. Barbara McClintock proposed that genes are not fixed on chromosomes, but that they can move around on the chromosome. At first her findings were discarded because they contradicted the genetic concept of the day. Today, her discovery of what she calls transposable elements has an established place in science.

Transposable elements allow antibiotic resistance and increased variation. The genes move because they are part of a small circular auxiliary genome called a plasmid, which enters and leaves the main genome at a specific place where there is a nucleotide sequence that is also present on the plasmid. Other genes move within small fragments of the genome called transposons. Together, transposons and plasmids produce genetic recombinations.

Integration at a new position also transfers the gene to that new position. The repositioning may be random, but occurs at sequence-specific insertion points which means that the process is orderly. The splicing and repositioning is carried out by enzyme systems and involves the transfer of complete information. 

Speciation

The evolutionary process by which new species arise.

Genome

A full set of chromosomes. A regular cell contains two full genomes.

Recombination of Chromosomes

Changes in chromosomal structure have been cited as important contributing factors in providing variation, and as a mechanism for speciation.

Changes in chromosomes can include changes in chromosome number or arm number, deletions, duplications, inversions, or even radical reorganizations of the genome.