Dr. Israa ayoub alwan Lec – 1-))   AL-Ma’moon University College Medical Laberatory techniques Department Molecular biology/ Second stage Dr. Israa ayoub alwan Lec – 1-))

Genetics is the study of inherited traits and their variation Genetics is the study of inherited traits and their variation. Sometimes people confuse genetics with genealogy, which considers relationships but not traits. With the advent of tests that can predict genetic illness, genetics has even been compared to fortunetelling! But genetics is neither genealogy nor fortunetelling—it is a life science. Inherited traits range from obvious physical characteristics, such as the freckles and red hair of the girl, to many aspects of health, including disease. Talents, quirks, behaviors, and other difficult-to-define characteristics might appear to be inherited if they affect several family members, but may reflect a combination of genetic and environmental influences.

Until the 1990s, genetics was more an academic than a clinical science, except for rare diseases inherited in clear patterns in families. As the century drew to a close, researchers completed the global Human Genome Project, which deciphered the complete set of our genetic instructions. The next step—surveying our genetic variability—was already underway. Today, genetics has emerged as an informational as well as a life science that is having a huge societal impact. Genetic information is accessible to anyone, and the contribution of genes to the most common traits and disorders is increasingly appreciated. Like all sciences, genetics has its own vocabulary. Many terms may be familiar, but actually have precise technical definitions.

Genes are the units of heredity, which is the transmission of inherited traits. Genes are biochemical instructions that tell cells, the basic units of life, how to manufacture certain proteins. These proteins, in turn, impart or control the characteristics that create much of our individuality. A gene is the long molecule deoxyribonucleic acid (DNA). It is the DNA that transmits information, in its sequence of four types of building blocks. The complete set of genetic instructions characteristic of an organism, including protein-encoding genes and other DNA sequences, constitutes a genome.

Nearly all of our cells contain two copies of the genome Nearly all of our cells contain two copies of the genome. Researchers are still analyzing what all of our genes do, and how genes interact and respond to environmental stimuli. Only a tiny fraction of the 3.2 billion building blocks of our genetic instructions determines the most interesting parts of ourselves—our differences. Comparing and analyzing genomes, which constitute the field of genomics, reveals how closely related we are to each other and to other species. Genetics directly affects our lives, as well as those of our relatives, including our descendants. Principles of genetics also touch history, politics, economics, sociology, art, and psychology.

Describe the Genetic Material “A genetic material must carry out two jobs: duplicate itself and control the development of the rest of the cell in a specific way,” wrote Francis Crick, codiscoverer with James Watson of the three- dimensional structure of DNA in 1953. Only DNA can do this. DNA was first described in the mid-eighteenth century, when Swiss physician and biochemist Friedrich Miescher isolated nuclei from white blood cells in pus on soiled bandages. In the nuclei, he discovered an unusual acidic substance containing nitrogen and phosphorus.

DNA Is the Hereditary Molecule:- In 1928, English microbiologist Frederick Griffith took the first step in identifying DNA as the genetic material. Griffith noticed that mice with a certain form of pneumonia harbored one of two types of Diplococcus pneumoniae bacteria. Type R bacteria were rough in texture. Type S bacteria were smooth because they are enclosed in a polysaccharide (a type of carbohydrate) capsule. Mice injected with type R bacteria did not develop pneumonia, but mice injected with type S did. The polysaccharide coat shielded the bacteria from the mouse immune system, enabling them to cause severe (virulent) infection. When type S bacteria were heated—which killed them but left their DNA intact—they no longer could cause pneumonia in mice. However, when Griffith injected mice with a mixture of type R bacteria plus heat-killed type S bacteria— neither of which, alone, was deadly to the mice—the mice died of pneumonia. Their bodies contained live type S bacteria, encased in polysaccharide. Griffith termed the apparent conversion of one bacterial type into another “transformation.”

How did it happen? What component of the dead, smooth bacteria transformed type R to type S? U.S. physicians Oswald Avery, Colin MacLeod, and Maclyn McCarty hypothesized that a nucleic acid might be the “transforming principle.” They observed that treating broken- open type S bacteria with a protease—an enzyme that dismantles protein—did not prevent the transformation of a nonvirulent to a virulent strain, but treating it with deoxyribonuclease (or DNase), an enzyme that dismantles DNA only, did disrupt transformation. In 1944, they confirmed that DNA transformed the bacteria. They isolated DNA from heat-killed type S bacteria and injected it with type R bacteria into mice. The mice died, and their bodies contained active type S bacteria. The conclusion: DNA passed from type S bacteria into type R, enabling the type R to manufacture the smooth coat necessary for infection.

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