A gene, the basic unit of heredity, is a segment of DNA that contains all the information necessary to synthesize a polypeptide (protein). Protein synthesis, “folding”, as well as tertiary and quaternary structures finally determine a large proportion of the body’s structure and function. Construction people have about 23,000 genes. Genes are contained in the chromosomes in the nucleus and in mitochondria. Normally located in the somatic (Nichtkeim-) nuclei of the human chromosome 46 in 23 pairs. Each pair consists of one maternal and one paternal chromosome. 22 chromosome pairs (autosomes) are usually homologous (matching size and shape as well as position and number of genes). The 23rd pair, the sex chromosomes (X and Y) determine the sex of the people and contain other functional genes. While women in each somatic cell nucleus have two (homologous) X chromosomes, they are in men an X and a Y chromosome (heterologous chromosomes). The genes on the X chromosome are responsible for many hereditary traits. The Y-chromosome is small and contributes, among other genes, genes which present a male sexual differentiation. Because the X chromosome has many more genes than the Y chromosome, many X-chromosome genes are not paired in men. In order to maintain the balance of genetic material between men and women, one of the X chromosomes is inactivated at random in women. The complete set of chromosomes in the cells of a human being is called karyotype. The germ cells (sperm and egg) undergo meiosis (meiotic division or reduction), in which the number of chromosomes to 23, d. H. half the chromosomes of the somatic cells is reduced. In meiosis recombination inherited from mother and father genetic information by crossing-over takes place (exchange of homologous chromosomes). When an egg is fertilized by a sperm, there is again the normal set of chromosomes (46). The genes are linearly along the DNA (or DNA Desosyribonukleinsäure) disposed of the chromosomes. Each gene has a specific location (locus), which is the same as a rule 2 for each of the homologous chromosomes. Genes parts (originating d. E. Of mother and father) on both of a pair of chromosomes occupy the same locus, the alleles can be mentioned. Each gene consists of a specific DNA sequence, and 2 alleles may have a slightly different or the same DNA sequence. Homozygosity means a pair of identical alleles and heterozygosity a pair of non-identical alleles for a given gene Some genes are present in multiple copies that can be side by side or at different positions in the same or different chromosomes. Meaning the genes genes are composed of DNA. The length of the gene determines the length of the protein for which the gene encodes. The DNA is a double helix in which nucleotides (bases) are paired. Adenine (A) with thymine (T) and guanine (G) with cytosine (C) combined. The DNA is transcribed during protein synthesis, in which one strand of the DNA as a template for messenger RNA (mRNA) is used. RNA has replaced the same base pairs such as DNA, except uracil (U), thymine (T). Parts of the mRNA migrate from the nucleus to the cytoplasm and then into the ribosome where protein synthesis takes place. The transfer RNA (tRNA) brings back each amino acid to the ribosome, where the growing polypeptide chain amino acid) is added. The sequence is determined by the mRNA. Once a chain is composed of amino acids, it folds under the influence of nearby chaperone molecules, so that a complex three-dimensional structure. The code in the DNA consists of triplets of 3 of 4 possible nucleotides. Certain amino acids are coded by specific triplets. Since there are 4 nucleotides, the number of possible triplets 43 (64). Since there are only 20 amino acids, there are redundant (additional) triplet combinations. Some triplets encode the same amino acids as other triplets. Other triplets can be used for items such. B. instructions for starting or stopping protein synthesis coding, and the order in which amino acids are combined or assembled. Genes consisting of exons and introns. Exons encoding amino acid components of the final protein. Introns contain additional information that affect the control and the rate of protein production. Exons and introns are transcribed together into mRNA, but the segments of introns are spliced ??later. Many factors regulate transcription, including antisense RNA which is synthesized from the DNA strand that is not transcribed into mRNA. In addition to DNA made chromosomes from histones and other proteins that affect gene expression, for example. B. which and how many proteins are synthesized from a particular gene. The genotype relates to a specific genetic composition and sequence; it determines which proteins are coded for production. In contrast, genome refers to the entire set of haploid chromosomes, including genes that contain them. The phenotype refers to the entire physical, biochemical and physiological appearance of a person, d. H. how the cell (and the body) works. The phenotype is determined by the type and amount of the proteins that are actually synthesized, d. H. characterized how the genes are in fact expressed. Expression refers to the process by which the information encoded in a gene, is used to control the arrangement of a molecule (typically protein or RNA). Gene expression depends on such factors. For example, whether a feature is dominant or recessive, the penetrance and expressivity of the gene (influences for gene expression), the degree of tissue differentiation (determined by tissue type and age), environmental factors and whether the expression is gender or chromosomal inactivation or genomic expression subject as well as other unknown factors. Epigenetic factors factors that affect gene expression without altering the genome sequence, epigenetic factors. The knowledge of the many biochemical mechanisms that mediate gene expression is growing rapidly. One mechanism is the variability in the removal of the introns (also known as alternative splicing). Because introns are spliced ??out, exons can be spliced ??out, which exons can then be assembled in multiple combinations, allowing many different mRNAs, which are capable of encoding similar but different proteins. The number of proteins that can be synthesized by humans, is> 100,000, even though the human genome has only about 20,000 genes. Other mechanisms that mediate gene expression include DNA methylation and histone modifications such as acetylation and methylation. DNA methylation often leads to switch off a gene. Histone similar coils, around which the DNA winds around. Histone modifications such as methylation increase or decrease the amount of proteins, which is synthesized by a specific gene. Histone deacetylation is associated with decreased gene expression. The DNA strand that is not transcribed to form mRNA can also be used as a template for the synthesis of RNA that controls transcription of the opposite strand. Another important mechanism involves microRNAs (miRNAs). MiRNAs are short hairpin RNAs (hairpin refers to the form, assume the RNA sequences, when they connect to each other), which suppress the target gene expression after transcription. They may be involved in the regulation of not less than 60% of the transcribed proteins. Characteristics and patterns of inheritance With the features it may be as simple characteristics such as eye color or as complex as susceptibility to diabetes. The expression of a characteristic can be a gene or several genes include. Some single-gene defects cause abnormalities in several tissues, this effect is called pleiotropy. Thus, can. As an osteogenesis imperfecta (often caused by abnormalities of a single collagen gene connective tissue disease), bone fragility, deafness, blue sclerae, dysplastic teeth hypermobility of the joints and heart valves error cause (osteogenesis imperfecta). Create a family tree The family tree can be used to represent a diagram of the inheritance pattern. It is also commonly used in genetic counseling. The conventional symbols used are for the individual family members and provide relevant health information about them (s. Symbols for building a family tree.). Some familial diseases with identical phenotypes have many different patterns of inheritance. Symbols for building a family tree. CHARTS symbols for each generation are located in the family in a row and numbered with Roman numerals, beginning with the older generation at the head and ending with the youngest generation at the lower end (s. Autosomal dominant inheritance., Autosomal recessive inheritance ., X-linked dominant inheritance and X-linked recessive inheritance). Within each generation, people are numbered from left to right with Arabic numerals. Siblings lists usually by age, with the oldest on the left side. Thus, each member of the family tree may be identified by two numbers (4 z. B. II). A spouse is also assigned an identification number. Key points The phenotype is determined by both the gene expression and the genotype. The mechanisms of regulation of gene expression are discussed and include intron splicing, DNA methylation, histone reactions and microRNAs.