It’s All in the genes

Why is genetics important? The modern science of genetics influences many aspects of daily life, from the food we eat to how we identify criminals or treat diseases. Understanding genetics is particularly relevant to many current issues such as: Cloning Stem cell and gene therapy Genetic testing for human diseases Recent privacy laws requiring personal medical information So……what is GENETICS?

Humans have always wondered how traits, such as eye and hair color are passed along from one generation to the next. The basic units of heredity are known as Genes. The study of the function and behavior of genes is called Genetics. In 1865, an Austrian monk named Gregor Mendel first studied inheritance patterns in a scientific way. He used the garden pea plants to determine that traits were inherited as separate units. His research formed the foundation for later scientific achievements in the field of genetics.

Jeans or genes? Every living organism, from the smallest bacteria to the largest animal carries a set of genes inside its cell. Genes are bits of biochemical information. DNA( deoxyribonucleic acid) is a coiled molecule that transmits the information . It usually exists in a double-stranded form that naturally winds together to form a double helix. The genes exist in segments along the length of the DNA molecule. Chromosomes are very long, continuous pieces of DNA which contains many genes . Although all humans share the same set of genes, individuals can inherit different forms of a given gene from their parents, making each person genetically unique…..except for identical twins. The inheritance process is Responsible for the variation in traits we see in nature like the color of a flower and human behavioral traits such as musical talent.

Mendel’s rules: a pattern of inheritance Mendel started his scientific study of on heritance by focusing on seven different traits in the pea plant. One he could readily identify was seed color. He found that : each trait had 2 forms: seeds were either green or yellow The colors didn’t blend, like if you mixed yellow and green paint That when he crossed a plant with green seeds with a plant with yellow seeds, the offspring all had yellow seeds and the green color disappeared. From this, he concluded that the gene for yellow seeds was dominant over its alternate gene for green seeds, which were recessive. This is known as an Allele: any one of a number of viable DNA codings of the same gene occupying a given position on a chromosome.

r Genotype= the combination of genes that code for a trait Phenotype= describes the physical manifestation of that trait In an organism like Mendel’s pea plant, 2 copies exist of each of its chromosomes so 2 alleles make up its genotype. Mendel’s plants had 2 alleles for the gene that controlled seed color. Yellow being dominant and green being recessive. When he crossed these offspring with each other, about 25% had green seeds,75% had yellow. Sex cells have only one set of chromosomes. When the egg and sperm fuse, the result is a baby with half of its chromosomes from one parent and half form the other.

Exception to the rule Since 1865, scientists have learned that sometimes genes do not easily conform to Mendel’s patterns of inheritance. Incomplete dominance: the inheritance of a dominant and recessive allele results in a blending of traits. For example, 4o’clock plants may have red, white or pink flowers. Quantitative inheritance: Mendel focused in traits determined by a single pair of genes resulting in a phenotype that was easy to distinguish. A tall plant is different from a short one, for example. But, some traits are not easy to distinguish like human skin color. This trait is determined by more than one pair of genes. At least 4 pairs of genes determine skin color.

Multiple alleles: Certain traits are controlled by multiple alleles that have complex rules of dominance. The gene for human blood type has 3 alleles. Gene linkage: Mendel studied traits in pea plants where one trait did not appear to influence another such as the plant’s height and texture. These 2 phenotypes occur randomly with respect to one another in a manner known as independent assortment. Today, scientists know that independent assortment occurs when genes affecting the phenotypes are found on different chromosomes. When genes appear near one another on the same chromosome, they are inherited as a single unit and are considered linked. Sex-linked traits: Most chromosome pairs consist of identical partners. There is one pair of chromosomes that are different, these are called the sex chromosomes because they determine the differences between male and female.

Breaking it down DNA carries all the information our cells need to function and carries hereditary information in a from that can be copied and passed from generation to generation. The genetic code is the biochemical instruction that is found within the gene and specifies the chemical structure of a particular protein. Proteins are composed of long chains of amino acids and the specific sequence of these amino acids dictates the function of each protein. DNA molecules form chains of building blocks called nucleotides. They consist of a sugar molecule called deoxyribose; a phosphate group and one of four bases: adenine (A), cytosine (C), guanine (G), and thymine (T). These are the elements that make up the DNA chain. In the cells of most organisms, 2 long strands of DNA join in a single molecule resembling a spiral ladder, commonly called a double helix. The bases of one strand join bases from another to form the rungs of the ladder, the pairing of bases.

The pairing of bases in the DNA double helix is highly specific—adenine always joins with thymine, guanine always links to cytosine. These base combinations play a fundamental role in the DNA’s function by aiding in the replication and storage of genetic information. Genes line up in a row along the length of a DNA molecule. A single gene can vary in length from 100 to more that 1,000,000 bases. Genes make up less than 2% of the length of a DNA molecule. The rest is made up of long, highly repetitive nucleotide sequences. Scientists now believe these nucleotide sequences may play a role in the survival of cells, and identifying these function is a thriving field of genetics research.

Reading the code New DNA is produced during mitosis=one nonsex cell splits into two; there are only two possible base pairings- A with T and G with C. This process is called DNA replication. During replication, the DNA strand unwinds and the chemical bonds joining the base pairs break, separating the DNA molecule into tow separate strands. Each strand directs the synthesis of another complimentary strand. Transcription is the process the DNA goes through to produce the proteins involved in every activity of the cell thereby producing an intermediary molecule called ribonucleic acid (RNA). Transcription involves the production of a special kind of RNA known as messenger RNA (mRNA). The mRNA consists of linked exons that together make up the genetic code for a protein.

Translation is the process that translates the information coded in the four bases found in mRNA into instructions encoded by the 20 amino acids used in the formation of proteins. Translation takes place in cellular organelles called ribosomes. They act like a clamp on workbench, holding the mRNA strand and coordinating the activity of enzymes and other molecules essential to translation. Transfer RNA (tRNA) is responsible for reading the genetic code and carrying the correct amino acid that the code specifies. This process continues repeatedly, with the new tRNA receiving the growing chain of amino acids, known as the polypeptide chain, from a resident tRNA. The process ends when the entire sequence of mRNA has been translated. The polypeptide chain falls away from the ribosomes as a newly formed protein, ready to go to work in in the cell.

Beyond mendel ------molecular genetics Genetic engineering-----the alteration of genes in an organism . These tools are used in industry to develop commercial products such as hardier crops, microbes the can break down oil slicks, decompose garbage an improve medicine. Recombinant DNA—DNA molecules are universal, all forms have the same DNA structure and the same four bases. Scientists have made use of these similarities in a technology called recombinant DNA. With this, scientists can create changes in the genetic makeup of an organism that would be unlikely to occur through natural processes.

The future of genetics Gene therapy: the insertion of one or more genes into an individual to treat disease, especially inherited(genetic) diseases. In experiments using gene therapy, researchers have replaced defective genes with normal alleles. A gene must be delivered to the cell using a carrier or “vector”. The vectors most commonly used in gene therapy are viruses. In some gene therapy clinical trials, cell fro the patients blood or bone marrow are removed and grown in a lab. This type of gene therapy is called ex vivo. The earliest success in human gene therapy involved treatment if infants who cannot produce an enzyme important to normal function of the immune system. These children have a devastating disease called severe immunodeficiency disorder(SCID), dubbed the bubble boy disease.

Genes and Society If scientists have developed genetic tests that shed light on a person’s personality , what dilemma’s could that present? Eugenics is the study of hereditary improvement of the human race by controlled selective breeding. Few areas of science hold as much promise or controversy as the area focused on what happens in our bodies at the molecular level. In the coming years we can expect much public debate about issues such as stem cell research and cloning. DNA fingerprinting and the right of privacy, prenatal genetic testing and the ethics of pregnancy termination and much more. Understanding basic genetics will provide you with the tools you need to make informed decisions about these important issues.