Genetics is the branch of biology that studies heredity and trait variation in organisms. It is concerned with how particular qualities or traits are transmitted from parents to offspring, and the molecular basis of those traits. Geneticists study genetic material (DNA) and mechanisms in attempt to determine how genes are related to variations of inherited characteristics among related or similar organisms. Geneticists also study the basis and possible treatment for genetic disorders such as Cystic fibrosis, Down syndrome, Hemophilia, or Sickle cell anemia.
The term genetics comes from the Greek word genno γεννώ which means give birth. The word genetics was first applied to describe the study of inheritance and the science of variation in 1905.
Almost since the beginnings of civilization, humans have been using selective breeding techniques to modify the genomes of plants and animals for their benefit. However, most of the credit for what we know as the principles of genetics is attributed to Gregor Mendel, who is often called the Father of Genetics. Mendel was a monk that lived from 1822-1884. He made multiple experiments with common pea plants. He wanted to know how certain traits/similarities were passed from the parent plant to the offspring. His experiments consisted of self-fertilization and cross-fertilization between the plants. He carefully studied seven different characteristics among the plants, the height (short or tall), the shape of the pods (inflated or constricted), smooth or wrinkled seed shape, and the color of the pea (yellow or green), to name a few. He developed pure breeds of the plants and then moved on to create 22 variations of pea plant with different combinations of the traits that the pure breeds had.
The Mendelian principles are what scientists have used to understand inheritance and the passing of traits in many organisms. [1] These principles are; The Principle of Dominance and Recessiveness, The Principle of Segregation and The Principle of Independent Assortment. Although not all plants are similar to the pea plants that Mendel used, his principles have formed the basis for selective breeding of several crops and plants. [2]
In 1866, Gregor Mendel studied the transmission of seven different pea traits by carefully test-crossing many distinct varieties of peas. Studying garden peas might seem trivial to those of us who live in a modern world of cloned sheep and gene transfer, but Mendel's simple approach led to fundamental insights into genetic inheritance, known today as Mendel's Laws. Mendel did not actually know or understand the cellular mechanisms that produced the results he observed. Nonetheless, he correctly surmised the behavior of traits and the mathematical predictions of their transmission, the independent segregation of alleles during gamete production, and the independent assortment of genes. Perhaps as amazing as Mendel's discoveries was the fact that his work was largely ignored by the scientific community for over 30 years![3]
Law of dominance:
Each trait is determined by two factors (alleles), inherited one from each parent. These factors each exhibit a characteristic dominant, co-dominant, or recessive expression, and those that are dominant will mask the expression of those that are recessive (See Genetic dominance).[3]
Law of segregation:
Each of the two inherited factors (alleles) possessed by the parent will segregate and pass during meiosis into separate gametes (eggs or sperm), which will each carry only one of the factors.[3]
Law of independent assortment:
In the gametes, alleles of one gene separate independently of those of another gene, and thus all possible combinations of alleles are equally probable.[3]
In sexually reproducing organisms, each gene in an individual is represented by two copies, called alleles—one on each chromosome pair. There may be more than two alleles, or variants, for a given gene in a population, but only two alleles can be found in an individual. Therefore, the probability that a particular allele will be inherited is 50:50, that is, alleles randomly and independently segregate into daughter cells, although there are some exceptions to this rule.[3]
The term diploid describes a state in which a cell has two sets of homologous chromosomes, or two chromosomes that are the same. The maturation of germ line stem cells into gametes requires that the diploid number of each chromosome be reduced by half. Hence, gametes are said to be haploid—having only a single set of homologous chromosomes. This reduction is accomplished through a process called meiosis, where one chromosome in a diploid pair is sent to each daughter gamete. Human gametes, therefore, contain 23 chromosomes, half the number in somatic cells—all the other cells of the body.[3]
Because the chromosome in one pair separates independently of all other chromosomes, each new gamete has the potential for a totally new combination of chromosomes. In humans, the independent segregation of the 23 chromosomes can lead to as many as 16 to 17 million different combinations in one individual's gametes. Only one of these gametes will combine with one of the nearly 17 million possible combinations from the other parent, generating a staggering potential for individual variation. But this is only the beginning. Even more variation is possible from the recombination between sections of chromosomes during meiosis as well as the random mutation that can occur during DNA replication. With such a range of possibilities, it is amazing that siblings look so much alike![3]
Epigenetics is the study of heritable changes in phenotype (appearance) or gene expression caused by mechanisms other than changes in the underlying DNA sequence, hence the name epi- (Greek: επί- over, above) -genetics. These changes may remain through cell divisions for the remainder of the cell's life and may also last for multiple generations. However, there is no change in the underlying DNA sequence of the organism; instead, non-genetic factors cause the organism's genes to behave (or "express themselves") differently.
In recent years, it has become increasingly clear that cellular inheritance is not limited to simple Mendelian genetics. The term epigenetics has been used to describe these types of inheritance that are not due to changes in the DNA nucleotide sequence, yet result in a new trait being passed from parent to offspring. Fixed DNA sequences wrapped around Histone proteins gives shape to the physical structure of the genome by coiling tightly inactive genes making them unreadable or inaccessible, while uncoiling active genes making them freely accessible. Maintenance of structure of the genome and strategic points of chemical locations upon DNA sequences are controlled by the epigenome and enable the genome to produce phenotype expression. Epigenetic chemical tags react to natural environmental stimuli and manifest through diet or stress for example.[4]
Epigenetics is an incredible field of study that encompasses a whole array of cellular processes. Some epigenetic mechanisms include: DNA methylation, histone modifications of DNA, genomic imprinting, noncoding RNAs, and X-chromosome inactivation. These result in changes in organisms or cell types, including cellular differentiation. Basically, epigenetics is a blanket term used to describe any type of cell memory passed on to offspring that does not involve direct manipulation of the DNA sequence.
The discovery of this process has serious implications for creation biology, given the fact that major phenotypic changes can occur without the Darwinian process of genetic mutation and natural selection.[5]
The scientific community generally assumes that cells formed without intelligent design. Therefore, existing genetic theories have been developed by those who are not looking for mechanisms that intentionally modify genetic information. Secular scientist believes that evolution is largely the result of biochemical accidents. Although geneticists and breeders have thoroughly established that genetic recombination is responsible for the variations of plant and animal breeds, we are still taught that random mutations produced the natural varieties of species such as the finches on the Galapagos islands. This contrast between fact and teachings is the result of atheistic theoretic necessity, which must propose that random reactions unreliant upon living systems are responsible for evolution.[6]
There are two sources of genetic variability: genetic recombination and mutation. Mutations are random, unintentional nucleotide alterations that can occur in many ways, such as by errors during replication, or by exposure to chemical mutagens. Genetic recombination, on the other hand, is performed intentionally by cellular machinery and its products remains largely uncharacterized. Both mutation and genetic recombination can modify genes, but we are being incorrectly taught that mutation is the primary source of variability driving evolution.[6]
Little is known about recombination, except that reactions occur between chromosomes, which alter the genome of each daughter cell so that no two offspring are ever identical. Given our level of understanding, we can not yet place a limitation on their ability to manipulate DNA. It is clear the genetic constitution of organisms is not static, and the cell's molecular machinery is altering genes and creating new alleles with each passing generation. The purpose of these reactions is clear. They occur so that organisms would be able to adapt physically and biochemically, and thereby occupy earth's broad range of habitats.[6]
It has been recognized for decades that the differences found among offspring from the same parents were the result of recombination events during meiosis. Domestic breeds, for example, are recombinants, not mutants. These rearrangements are being performed by design to provide evolutionary potential to all organisms. Contrary to popular beliefs, evolution through recombination is not random, but is instead highly systematic. In comparison, mutations are random destructive changes that destroy information. Mutations are most typically deleterious, disruptive to genome function, and corrected by the cell when detected. Evolution truly occurs through a history of genetic recombination and natural selection, but the way it is taught, you would never know anything but mutation was involved.[6]
Contrary to what the evolutionists teach, adaptation is the result of systematic and intentional cellular reactions. However, in contrast to typical creationist perceptions, this change is not limited to the variability originally possessed by the organism. God created a cellular machinery that is performing a level of self genetic engineering. This process is creating new information and able to modify organisms so dramatically we can frequently not recognize them as related. The physical manifestations of these reactions is hard to predict, and it is also quite possible that genetic editions are being made in direct response to environmental demands.[6]
Gene Duplication is the central tenet of Neo-Darwinism. However, there has never been any evidence that genetic novelty can occur from this process. In fact, very recently research was conducted by Joseph Esfandiar Hannon Bozorgmehr (Complexity 22 Dec. 2010) and he could find no example of gene duplication that could be applicable to the theory. He went on to say:
| “ | Gene duplication and subsequent evolutionary divergence certainly adds to the size of the genome and in large measure to its diversity and versatility. However, in all of the examples given above, known evolutionary mechanisms were markedly constrained in their ability to innovate and to create any novel information. This natural limit to biological change can be attributed mostly to the power of purifying selection, which, despite being relaxed in duplicates, is nonetheless ever-present... ...the various postduplication mechanisms entailing random mutations and recombinations considered were observed to tweak, tinker, copy, cut, divide, and shuffle existing genetic information around, but fell short of generating genuinely distinct and entirely novel functionality... ...Gradual natural selection is no doubt important in biological adaptation and for ensuring the robustness of the genome in the face of constantly changing environmental pressures. However, its potential for innovation is greatly inadequate as far as explaining the origination of the distinct exonic sequences that contribute to the complexity of the organism and diversity of life. Any alternative/revision to Neo-Darwinism has to consider the holistic nature and organization of information encoded in genes, which specify the interdependent and complex biochemical motifs that allow protein molecules to fold properly and function effectively. [7] |
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Creation geneticists interpret the cellular mechanisms behind genetics (heredity) based on the assumption that the Biblical creation described in the book of Genesis was a real and historical event, and seek primarily to show that the transmission and inheritance of traits are best interpreted within this worldview. The following are geneticists who hold to the creation view.
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