Genes

Heredity and variation is the basis of genetics. Humans applied knowledge of genetics in prehistory with the domestication and breeding of plants and animals. In modern research, genetics provides important tools for studying the function of a particular gene, such as analysis of genetic interactions. In organisms, genetic information generally is carried in chromosomes, which are represented in the chemical structure of particular DNA (deoxyribonucleic acid) molecules.

Genes encode the information necessary for the synthesis of amino acid sequences in proteins, which play an important role in determining the final phenotype, or appearance of the body. In diploid organisms, a dominant allele on one chromosome masks the expression of a recessive gene on the other.

To code phrase is often used in the sense of a gene contains instructions on how to build a particular protein, which in the gene that codes for protein. The "one gene, one protein" concept is now known to be simple. For example, a single gene producing multiple products, depending on how it regulates transcription. Genes encoding the sequences of nucleotides in mRNA, tRNA and rRNA, required for protein synthesis.

Genetics determines the amount (but not all) of the appearance of organisms, including humans, and perhaps how they act. Environmental differences and random factors also play a role. Monozygotic (identical) twins, a clone resulting from the division of an embryo, have the same DNA, but with different personalities and fingerprints. genetically identical plants grown in colder climates incorporate shorter and less saturated fatty acids to avoid stiffness.

Human beings have cells with 46 chromosomes - 2 sex chromosomes and 22 pairs of autosomal (not sex) chromosomes. Males are "46, XY" and women "46, XX." These chromosomes consist of very long DNA molecules in combination with proteins.

Genes are defined by intervals along a molecule of DNA. The location of the gene is called locus. Most genes carry information for making a protein.

The pairs of autosomal chromosomes (one from mother and father) carry basically the same information. That all have the same genes, but there may be slight variations in these genes. These small differences occur in less than 1% of DNA sequence and produce variants of a particular gene are called alleles.

The information in the nucleotide sequence of a gene is transcribed to mRNA (messenger RNA) by enzymes in the cell nucleus and then translated into a protein in the cytoplasm. This protein may be a bit of tissue. Could be an enzyme that is involved in a chemical reaction, or maybe a hormone. There are many other possible functions of proteins.

If a gene is abnormal, may lead to an abnormal protein or an abnormal amount of normal protein. Since autosomal chromosomes are paired, there are two copies of each gene, one from each parent. If any of these defective genes, the other taking enough protein, so that no disease is seen. This is called a recessive disease, and the gene is said to have inherited a recessive model.

But if only one abnormal gene is needed to produce the disease, which is called a dominant hereditary disorder. In the case of a dominant disease, if one abnormal gene is inherited from the father or mother, the child will likely show the disease.

A person with an abnormal gene is called heterozygous for this gene. If a child receives an abnormal recessive disease gene from both parents, the child will see the disease and homozygous for that gene.

If both parents are heterozygous for each gene of a recessive disease, in particular, that every child has a probability of 25% homozygous for this gene, and therefore shows the disease. If one parent is homozygous and heterozygous others, so every child has a probability of 50% homozygous.

Today, many genome projects to add tens of thousands of public nucleotide databases every day, to explore gene function often begins with a sequence of DNA. Here the challenge is to translate the sequence into the function. One approach, referred to earlier in this chapter, is looking for database and characterized proteins that have similar amino acid sequences of proteins encoded by a gene, and from there to use some of the methods described in § previous study for another function of genes. But to directly address the problem of how a gene in a cell or organism, is the most effective approach to study mutants that lack either the gene or expression of a modified version of this. Determine cellular processes are disrupted or threatened such mutants, and often provides a window into the biological function of a gene.