Human Cloning

Human Cloning

What is Human Cloning?
Cloning an organism involves replicating the DNA of that organism in a new organism that, as a result, has the same exact features and characteristics. Human Cloning would mean recreating the person that is being cloned. With the successful cloning of Dolly The Sheep, Human Cloning, long the staple of science fiction, is on the verge of becoming a reality.

How would Human Cloning work?
Human Cloning, if it is ever done, will be carried out by the same method that brought forth Dolly, Reproductive Cloning.

In Reproductive Cloning, the nucleus is removed from a body cell of the organism to be cloned and this nucleus is inserted into an enucleated egg, that is, an egg whose nucleus has previously been removed.

The egg with the new nucleus is then treated to electric or chemical treatment to simulate cell division. The resulting embryo is transferred to a host uterus to develop properly and eventually be given birth to.

The new-born organism will be a replica of the original organism, but not the exact same actually, since it will have DNA derived from both the organism as well as the egg.

Why would Human Cloning be done?
Cloning animals, especially endangered species, is one way of preserving the species from dying out entirely. But why would anyone want to clone human beings? There are enough of us already on the planet without resources enough for the well-being of all of us. So why bother to clone?

Well, one reason is pure scientific research. We've already come a long way. After Dolly, scientists have managed to clone various animals. So cloning humans seems the next logical step and a very important one it would be too.

Cloning humans could also prove a major breakthrough as far as cloning for therapeutic purposes is concerned. Cloning could be used to produce new organs for organ transplants. Since the cloned organ, produced from a body cell of the person needing the transplant, would have the same genetic code, there would be less risk of the body rejecting the new, transplanted organ. Cloning could also be used to treat Cancer, Alzheimer's and Parkinson's Diseases, and host of other illnesses.

Cloning would allow infertile couples to have their own genetic offspring or otherwise normal couples to order designer babies. It could also be used to bring back to life your dead ancestors. So if you want to give birth to your great-great-grandmother, you can. Just as long you managed to preserve some samples of her body cells.

One American couple reportedly is willing to pay $500,000 to clone their dead infant daughter.

And then there are some who would like to clone themselves and thereby achieve eternal life.

Is it ethical to go ahead and clone humans?
Well, sometimes one of a kind is more than one can tolerate. But, on the serious side, many of the leading Scientists involved in cloning research, like Ian Wilmut and Richard Gardner, have expressed serious doubts and ethical dilemmas over the cloning of human beings.

Firstly, reproductive cloning is not yet a fool-proof method. It took 272 attempts before Dolly was produced. This means 272 embryos either failed to develop properly or were discarded as defective. In other cases, if the embryos weren't miscarried, a large percentage of the animals born showed a high degree of abnormality and died quickly or had to be euthanized. Those successfully cloned have showed many health problems and none have lived to a ripe old age so far.

Now, since human beings consider themselves a class apart, obviously many moral problems would arise with treating defective human embryos or new-born, handicapped babies in the very same manner.

There is also no way of predicting what the intelligence level and capabilities of a human clone would be. What would be the psychological and societal implications for it as an individual? What kind of a life or future would it have? Since we don't know, many people consider it unethical to go ahead and clone.

But that argument doesn't hold much water with others. After all, we have no way of knowing exactly what sort of a person a normally conceived embryo will turn out to be either.

Is Human Cloning legally allowed?
Reproductive Cloning of Humans is banned is many countries around the world, including the USA and the UK, and allowed in some. Therapeutic Cloning is allowed to some degree, but there is already a clamor against it from religious and pro-life organizations, many of whom are more acquainted with its theological implications than its theoretical possibilities.

What is Human Gene Therapy

What is Human Gene Therapy

Human gene therapy is a milestone in the field of medical science, applicable for treatment of chronic health conditions and genetic disorders. However, there are certain factors related to the effectiveness of gene therapy techniques such as autoimmune responses, vectors, multigene disorders...

A gene is a stretch of DNA (deoxyribonucleic acid) that contains nucleotide sequences. Based on the nucleotide sequences, specific proteins are synthesized, which in turn, are responsible for expression and function of body cells and tissues. If there is any alteration in the genetic sequence, the protein synthesis is disturbed. In such a condition, the cells and tissues are unable to perform their normal function, leading to genetic diseases.

What is Human Gene Therapy

Human gene therapy is a scientific technique, by which a segment of nucleotide sequence or gene is inserted into an individual's cell for the purpose of treating diseases. The main principle behind gene therapy is to restore the normal functioning of cells and tissues by replacing abnormal or mutated genes. In simple terms, it is a method of correcting defective genes. There are several ways of implementing gene therapy; inserting a normal gene in the genome to replace a defective gene and changing the regulation for expression of a specific gene. Another method of gene therapy is to apply selective reverse mutation so that the defective gene returns to its original form.

In majority of human gene therapy cases, a normal therapeutic gene is inserted by using a vector or a carrier molecule. As the name suggests, the vector serves the purpose of delivering the normal gene to the target cell. As the vector incorporates the therapeutic gene in the target cell (for example liver cells), the therapeutic gene starts producing functional proteins, thus restoring the normal function of the target cell. While speaking about the vector or carrier molecule, various types of viruses such as retrovirus and adenovirus are used for the purpose. Before using any of these viruses as vectors, the genomic content is changed by removing disease-causing gene and replacing it with therapeutic gene.

Pros and Cons of Human Gene Therapy

There are many potential side effects of using viruses as vectors, some of which include target-related problems, inflammatory response of the immune system and at times, toxicity. A more recent technique of human gene therapy is to introduce the normal gene directly to the target cell without using vectors. Though this method sounds comparatively easy, it is not applicable to all types of target cells. Another disadvantage of this method is that it requires large amount of DNA.

A major drawback of gene therapy is the short-term effectiveness of the therapeutic gene after introducing into the target cell. It is the dividing cells present in the body that prevents the expression of therapeutic genes. After inserting the foreign therapeutic gene into the target cell, it is necessary to regulate the autoimmune responses of the body. Human gene therapy is less effective for multigene problems (presence of many defective genes).

Though the technology of human gene therapy is not so advanced in the present scenario, it has already widened the scope of medical science. As all genetic disorders and most of the chronic diseases involve malfunctioning of the genes, gene therapy is a promising technique for treatment of such severe health conditions. Genetic researches based on human gene therapy are ongoing to discover treatment options for chronic medical conditions such as heart disease, cancer, cystic fibrosis and AIDS. Nowadays, private grants as well as government grants are provided so as to encourage studies on human gene therapy.

Polygenic Traits

Polygenic Traits

Polygenic traits are different physical characteristics of individuals, due to specific inheritance patterns. It is responsible for difference in phenotypic makeup of individuals. Physical appearance of individuals is determined by genotypic ratio and chromosomal inheritance. This phenomenon was put forth by Mendel, popularly known as 'Mendel's Laws of Inheritance'. In case of polygenic traits, the characteristic features of individual result from interaction of different genes. In layman's language, we can exemplify with an individual having high blood pressure. High blood pressure does not result due to activity of single gene. This particular phenotype is the net result of interaction of cholesterol genes, obesity genes, transporter genes and addictive genes. The combined effect of these multiple genes or polygenes, is the reason behind high blood pressure. That was an elementary approach of polygenic traits. You might also like to read more on interesting aspects of human genetics.

Genetic Phenomenon of Polygenic Traits

Polygenic traits is not only observed in human beings but are also present in animals, birds, insects, flies etc. In terms of human genetics, polygenic traits is defined as, inherited characteristics when two or more genes are involved in determining the phenotype of individuals. Thus, the cumulative effects of genes are responsible for determining many traits like, weight, height, shape, color and metabolic rate of individuals. They characteristics of polygenic traits are:

    Polygenic traits do not follow Mendel's patterns of inheritance.
    They are recognized by their expressions that result from gradation of continuous variation.
    Additive effects of two or more separate pair of genes control continuous variation.
    The traits are quantified by measuring the variation, rather than counting.
    The phenotypic expression vary in wider range as a result of contributing pairs of genes.

Polygenic traits are also known as quantitative traits or multifactorial traits. To understand these synonyms, you need to understand the mechanism of genetic inheritance. Polygenic traits are controlled by two or more genes at different loci on different chromosomes or it is the trait that is controlled by non-allelic genes. They are known as quantitative traits as their phenotypic expression is dependent on multiple alleles located on different chromosomes. You might also like to read about genetic drift.

The quantitative aspect (e.g how tall or how short) or phenotype of the individual is represented as trait value. When frequency of individuals with polygenic traits is plotted against trait value, the graph is bell shaped. Polygenic traits are result of additive effects of contribution of each genes in loci and therefore they do not follow typical dominance and recessive patterns. The second aspect of polygenic genes are, the traits are determined by environmental variations. It means that an individual can be genetically same, but can differ in their physical appearance, while rest are congenial disorders. Polygenic traits can be determined by knowing the number of quantitative trait loci, that plays an important role in determining the genetic architecture of an individual. Read more on genetic disorders in humans.

Examples of Polygenic Traits in Humans

Examples of polygenic traits, governed by environmental factors are:

    Weight
    Height
    Eye color
    Intelligence
    Behavior
    Skin color

Polygenic traits examples with disorders in genetic components are:

    Cleft palate
    Cancer
    Diabetes
    Autism
    Congenital heart disease
    Congenital dislocation of hip
    Talipes
    Pyloric stenosis
    Neural tube defects
    Schizophrenia
    Diabetes Mellitus
    Glaucoma
    Hypertension
    Manic depression
    Ischaemic heart disease
    Maniac depression
    Eczema
    Dermatitis
    Spina bifida
    Anencephaly

Read more on:

    Understanding Genes
    Facts about Human Chromosomes

Polygenic traits is an important genetic phenomenon, governing different variations and characteristic in individuals. Polygenic traits in humans are interesting to study and observe.

NOTE
Glossary of Terms

    Genes: Unit of heredity in a living organism.
    Chromosomes: Organized structure of DNA and protein that embeds genes.
    Alleles: Different forms of genes in a single genetic locus.
    Genetic Locus: Specific location of gene or DNA sequence in chromosome.
    Phenotype: Observable characteristics, morphology, physiological properties of an organism
    Genotype: Information in genes that determines the phenotypic traits.
    Quantitative Trait Locus (QTL): Region of DNA, found in different chromosomes, associated with a particular phenotypic trait.
 

Facts about Human Chromosomes

Facts about Human Chromosomes

Human chromosomes are strands of DNA carrying all the important information about the human being. To look at some interesting facts about the human chromosomes,

A chromosome, by definition, is a threadlike strand of DNA in a cell nucleus that carries genes, the units of heredity in a linear order. Human beings have 22 chromosome pairs and a pair of sex chromosomes. Apart from genes, the chromosomes also contain regulatory elements and nucleotide sequences. They house the DNA-bound proteins, which control the functions of the DNA. Interestingly, the word chromosome originated from the Greek word, 'chrome' meaning color. Chromosomes got their name owing to their property of being stained by dyes. The structure and nature of chromosomes varies across different kinds of organisms. Human chromosomes have always been a subject of interest for the researchers working in genetics. The wide range of factors that human chromosomes determine, the abnormalities they are responsible for and their complex nature have always invited interest of many. Let us look at some interesting facts about the human chromosomes.

Facts about Human Chromosomes
Human cells have 23 pairs of nuclear chromosomes. A chromosome is made up of a DNA molecule that contains genes. A chromosomal DNA molecule contains three nucleotide sequences, which are required for replication. On staining the chromosomes, the banded structure of the mitotic chromosomes becomes apparent. Each band contains numerous DNA nucleotide pairs.

Human beings are sexually reproducing species and have diploid somatic cells having two sets of chromosomes. One set is inherited from the mother while the other one from the father. As against the body cells, the reproductive cells have a single set of chromosomes. The crossover between chromosomes results in the creation of new chromosomes. The newly created chromosomes are not inherited from any single parent. This brings about the fact that not all of us exhibit traits that are directly derived from one of our parents!

There are 24 distinct human chromosomes out of which 22 are autosomal chromosomes and the remaining two are sex-determining chromosomes. The autosomal human chromosomes are numbered from 1 to 22 in the decreasing order of their size. Every individual has two sets of the 22 chromosomes, X chromosome from the mother and an X or a Y chromosome from the father.

An abnormality in the content of the chromosomes of a cell can cause certain genetic disorders in human beings. Chromosomal abnormalities in human beings are often responsible for the appearance of the genetic disorder in their children. Those with chromosomal abnormalities are often only the carriers of the disorder while their children actually exhibit the disorders.

Chromosomal aberrations are caused by a variety of factors namely, deletion or duplication of a part of a chromosome, the inversion, which is the reversal of direction of a chromosome or a translocation wherein a part of a chromosome breaks off to attach to some other chromosome.

An extra copy of chromosome 21 is responsible for the very well-known genetic disorder that is known as the Down's syndrome. The trisomy of chromosome 18 results in the Edwards syndrome that may cause death in infancy.

The deletion of a part of the fifth chromosome leads to a genetic disorder known as 'cri du chat', meaning 'cry of a cat'. The human beings affected by this disorder show a cat-like crying in childhood and are often mentally retarded.

The disorders caused by sex chromosomes include the Turner syndrome wherein female sexual characteristics are present but underdeveloped, the Triple-X syndrome in girls and the XXY syndrome in boys, both causing dyslexia in the affected individuals.

Chromosomes were first discovered in plants. Van Beneden's monograph on the fertilized eggs of a roundworm, led the research further. Later in time, August Weismann proclaimed that the germ line was different from the soma and he discovered that the cell nucleus housed the hereditary material. He also proposed that fertilization results in a new combination of chromosomes.

These discoveries were cornerstones in the field of genetics. Researchers have achieved a sufficient amount of knowledge of human chromosomes and genes but there is still a lot to be discovered.

Interesting Aspects of Human Genetics

Interesting Aspects of Human Genetics

Human genetics revolves around the influence of genes on human nature and behavior patterns. It is associated with certain personality traits as well as disorders in human beings. Let us look at the interesting aspects of human genetics.

The fact that human genetics can answer questions related to diseases in human beings, their treatment, the genetic disorders and more importantly the human nature, makes this field interesting. It includes different fields such as classical and clinical genetics and genomics. Human genetics deals with the study of the inheritance pattern in the human beings. The potential uses of human genetics in the study of human nature and its prospective applications in medicine have made it a subject of interest for one and all.

Interesting Aspects of Human Genetics

Gregor Mendel studied the inheritance of the traits in living beings. He concluded that inheritance depends upon discrete units known as genes and he came up with a model of inheritance. He deduced that the inheritance of traits follows certain laws. For his significant work in genetics, Mendel is known as the father of genetics.

Inheritance traits in human beings are either autosomal or X or Y linked. Autosomes are the non-sex chromosomes whereas the X-linked and the Y-linked genes are found on the sex chromosomes. Let us look at each of them.

    In case of autosomal recessive inheritance, a trait or a disorder is passed on through families. For a recessive trait to show in humans, two copies of that trait are required. Since two copies of the disorder or the trait are needed for its display, it can remain hidden for generations together. Many human beings can be unaware of the fact that they are acting as carriers of the trait or disorder.
    Autosomal dominant inheritance is a pattern wherein a single copy of a trait is sufficient for it to appear in a human being. If one of the parents has this trait, it can be displayed in their children.
    Traits inherited from the sex chromosomes include the X-linked and the Y-linked inheritance. X-linked genes can be autosomal or recessive. Recessive X-linked disorders are common among males. As a father passes his Y chromosome to his son, X-linked traits or disorders are inherited from the maternal side. The expression of X-linked traits in the females depends on their zygosity for the trait. When a female is homozygous for a particular trait or disorder, it means that she carries two identical copies of the gene affecting that trait. In case she is heterozygous for a particular disorder, it means that she has two different alleles for that disorder. Homozygous females display X-linked disorders while the heterozygous females become carriers for the disorder. Y-linked disorders are carried on the Y chromosome. As it is present only in males, a Y-linked trait is transferred from a father to his son.

Apart from the nuclear DNA, human beings possess mitochondrial DNA. It is believed that the mitochondria are descended from a proteobacterium, which merged with eukaryotic cells, around two billion years ago. Mitochondrial DNA is about 16 KB long. A human being inherits mitochondria from his/her mother. This makes it evident that DNA can be used to track a person's maternal lines. Interestingly, in some species like the mussels or insects like the honeybees, paternally inherited mitochondria are observed. A single case of paternal inheritance of mitochondria was reported in humans. But it was associated with infertility.

Genes play a vital role in personality characteristics and human behavior. Facial features are linked to genetic constitution of an individual. A human being inherits the characteristics like facial dimples, color of the iris, the structure of the earlobe and other such traits through the genes. Attributes such as the overall stature and susceptibility to certain diseases are also inherited genetically.

Human genetics has evolved to a level where we have been able to manipulate the genetic constitution of an embryo to a certain extent through genetic engineering. The knowledge of human genetics has led us to be able to enhance the positive traits in humans while removing the negative ones. The various interesting aspects of human genetics have unfolded the mysteries of the physical and psychological characteristics of humans and opened doors to the betterment of human life.