Genetics Courses Open University
The 21st century began with the completion of the first draft of the complete sequence of the human genome. Coupled with new techniques for intervening in genetic disorders such as mass genetic screening, gene therapy and genetic manipulation these are among the most fraught areas of debate in modern biology and medical science. Such revolutionary techniques bring with them profound social and ethical dilemmas as they open up the possibility of redirecting our future evolution.
The science of genetics
The study of genes began in 1900 when it was shown that genes govern inheritance in many different creatures. In 1907 it was shown that the same patterns of inheritance could account for the transmission of eye colour in humans. However, not until 1953 was the structure of DNA deduced by Watson and Crick. By the end of the 20th century, many thousands of genes had been discovered and their sequences determined, including many that have roles in disease. These genes are scattered throughout the genome.
Our genetic structure
Every cell of a human being has two sets of twenty-three chromosomes and every cell of a given individual has exactly the same DNA in it, with the exception of the gamete cells, that is to say the sperm cells and the egg cells. Now these specialised kinds of cells have only one set of chromosomes. So when an egg is fertilised by a sperm, one copy of chromosomes comes from the father and one copy of chromosomes comes from the mother.
Together they form a nucleus with two sets of chromosomes. So the fertilised egg cell, the zygote, has two sets of chromosomes. At each cell division which leads up to the formation of a fetus, and then a baby, and then an adult human being, these chromosomes are replicated and equally partitioned between each cell, so that each cell of the adult individual has the same set of chromosomes, the same set of genes - two sets of chromosomes, two copies of each gene.
Along the length of DNA in each chromosome are these units called genes, which is why DNA is referred to as the genetic material. Our characters - the structure and appearance of an individual, such as blue or brown eye colour - depend on the functions of genes. Genes also contribute to a person's behaviour and health, including susceptibility to certain diseases, such as heart disease.
Human genome sequence
When genetics is explained in the news there's usually a graphic of a whole string of lettering. This is the human genome sequence. What you see on the news is an alphabetic representation of the molecular structure of DNA.
The information is stored in the DNA as a series of letters: A, C, G, and T - that's the end product of the experiment. Each letter represents a different chemical (adenine, cytosine, guanine and thymine).
Life Sciences CourseMate Online Study Tools (with eBook) to Accompany Yashon/Cummings' Human Genetics and Society, 2nd Edition, [Web Access], 1 term (6 months)
Digital Software (Cengage Learning-158940-158940)