Summarize factors that may lead to different types of mutations

• factors include chemical (e.g. PCB), biological (e.g. virus), and physical (e.g. radiation)


Mutations are inheritable changes in the genetic material (DNA) of an organism. Mutations may take place in any cell. Cosmic rays, X rays, ultraviolet radiation, and chemicals that alter the DNA are called mutagenic agents (or mutagens). By changing the arrangement of the nucleotides (C,G,A and T) in the double helix, the mutagen changes the genetic code. The shift in a single nucleotide can lead to the production of a new protein from the instructions. The new protein has a different chemical structure and, in most cases, is incapable of carrying out the function of the required protein. Without the required protein, cell function is impaired, if not completely destroyed. Although some mutations can, by chance, improve the functioning of the cell, the vast majority of mutations produce adverse effects.


A mutation can be as simple as a single base change in DNA or a mutation can affect an entire chromosome or section of a chromosome.


Chemical Mutagens – Chemicals such as PCBs can interfere with correct DNA replication by inserting themselves into the DNA and distorting the double helix. Other chemicals can cause changes in the chemical structure of the bases and change their pairing properties.


Biological mutagens – A virus can insert its DNA into a gene that controls normal cell division, causing the cell to become cancerous.


Physical mutagens – Radiation can cause direct or indirect DNA damage. Direct damage is caused when the radiation strikes the DNA molecule itself. Ex. Occasionally, X rays will break the backbone of the DNA molecule. Special enzymes will repair the break but the spliced segment may not get placed in the proper position. The misplaced segment may alter the entire library of genetic information. Indirect damage occurs when other molecules, such as water, are struck then cause disruption to the DNA.


Society is now both more aware and concerned about the presence of mutagens in the environment. Mutagens are ubiquitous; some are naturally present in plants, many are produced by combustion of organic materials (including cooking), and others are products of industry. Given daily exposures to mutagens it is natural to ask which agents are responsible for birth defects and what reproductive risks may arise from specific exposures.


Experimental data indicate that most dominant mutations induced in germ cells at high levels of exposure are lethal. Conceptions carrying dominant lethal genes are likely to abort early or even fail to implant. Thus the perceived effect is, again, infertility. Recessive mutations induced by mutagens will not be detected until they become homozygous in future generations and many changes in sequence in non-coding regions of the genome will simply remain silent.


Distinguish among positive, neutral, and negative effects of various mutations


Positive effects – Some mutations improve cell function or the ability of an organism to survive in its environment. Ex. A bacterium could acquire resistance to an antibiotic.


Negative effects – Some mutations result in reduced cell function or decreased survival of the organism in its environment. Ex. Hemophilia


Neutral effects – Mutations with no harm benefit to the cell or organism. Ex. Mutations occurring in non-coding regions of the DNA (“silent mutations”).


The distinction between deleterious, neutral, and adaptive mutations is a fundamental problem in the study of molecular evolution. Two significant quantities are the fraction of DNA variation in natural populations that is deleterious and destined to be eliminated and the fraction of fixed differences between species driven by positive Darwinian selection.


WHILE the fixation of adaptive mutations may be viewed as the crux of Darwinian evolution, it has long been argued that the majority of DNA changes that accumulate over time are not adaptive but neutral, fixed by stochastic fluctuations in a finite population (KIMURA 1983 Down). Indeed, except for a few proteins with extremely high rates of evolution, evidence for adaptive evolution at the molecular level has been elusive (NEI 1987 Down). Much more is known about deleterious mutations and H. J. Muller argued in an influential address that the reduction in mean population fitness due to these mutations may constitute a considerable human health concern (MULLER 1950 Down).



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Analyse implications of current and emerging biomedical, genetic, and reproductive technologies


Biomedical technology involves the application of engineering and technology principles to the domain of living or biological systems. Usually biomedical denotes a greater stress on problems related to human health and diseases. Biomedical engineering combined with Biotechnology is often called Biomedical Technology or Bioengineering. Biological engineers are similar to biologists in that they study living organisms. They are engineers because they have a practical design aim in mind - they use research to create usable tangible products. In general, biological engineers attempt to 1) mimic biological systems in order to create products or 2) modify and control biological systems so that they can replace, augment, or sustain chemical and mechanical processes.


Genetic technologies involve changing the genes in a living cell. There are two types of genetic modification: non-inheritable genetic modification (somatic) and inheritable genetic modification (germline). Non-inheritable genetic modification changes the genes in cells other than egg or sperm cells. Diseases caused by defective genes could be treated by modifying the genes in affected cells. These changes are not passed to future children. Applications of this sort (such as gene therapy) are being pursued in clinical trials, and are generally considered to be socially acceptable.


Reproductive technology is a term for all current and anticipated uses of technology in human and animal reproduction, including:

    * artificial insemination

    * artificial wombs

    * cloning (see human cloning for the special case of human beings)

    * cryopreservation of sperm, oocytes, embryos

    * embryo testing

    * embryo transfer

    * genetic engineering

    * hormone treatment to increase fertility

    * in vitro fertilization

          o intracytoplasmic sperm injection

    * in vitro parthenogenesis

    * preimplantation genetic diagnosis (PGD)

    * reprogenetics

    * sperm selection

    * Testicular sperm extraction (TESE)


Assisted reproduction or assisted reproductive technology (ART) is sometimes used as a term for fertility treatment using reproductive technology.

Contraception may also be viewed as a form of reproductive technology, as it enables people to control their fertility.

Many issues of reproductive technology have led to ethical issues being raised, since it often alters the assumptions that lie behind existing systems of sexual and reproductive morality.


There are risks and benefits associated with biotechnology. For example, the removal of hemophilia or other serious disorders from the gene pool is a benefit because people would no longer suffer from a chronic condition. An example of a risk is going too far in selecting the genetic makeup of future children.


Possible risks:

- Relying on eugenics, or selecting the genetic makeup of future children. This practice may give people the power to control some personal traits, such as having blond hair or being tall. Taken to an extreme, this could eliminate some traits.

- Using biotechnology before exploring other options, particularly in reproductive medicine. For example, technology enables scientists to implant an egg from one woman into the uterus of another. But it may not be a good idea to use this technique before trying less extreme techniques first.


Possible benefits:

- Eliminating genetic diseases. For example, geneticists think it may be possible to eliminate genetic diseases such as Tay-Sachs through careful and methodical screening programs.

- Screening unborn babies. This refers to screening for genetic disorders either before a pregnancy takes place or in the early months of a pregnancy. More information would give prospective parents more options in dealing with their infants' problems.

- Treating diseases. For example, scientists are working on ways to insert cells from embryos into cancerous cells as a way to stop the growth of cancer.


Biotechnology is a powerful tool and scientists have had to consider many ethical issues surrounding it. As a result, the new field of bioethics has emerged. Bioethics is the study of the ethical implications of biological research and applications, especially in medicine; it involves examination of the benefits and the risks of biotechnology.