The impact of genetics on nursing is significant. The American Nurses Association (ANA) officially recognized genetics as a nursing specialty. This effort was spearheaded by the International Society of Nurses in Genetics (ISONG), which also initiated credentialing for the Advanced Practice Nurse in Genetics and the Genetics Clinical Nurse. ANA and ISONG have collaborated in the establishment of a scope and standards of practice for nurses in genetics practice. Essential Nursing Competencies and Curricula Guidelines for Genetics and Genomics were finalized in 2006. They reflect the minimal genetic and genomic competencies for every nurse regardless of academic preparation, practice setting, role, or specialty.
Cell as The Basic Unit of Biology
- Cytoplasm—contains functional structures important to cellular functioning, including mitochondria, which contain extranuclear deoxyribonucleic acid (DNA) important to mitochondrial functioning.
- Nucleus—contains 46 chromosomes in each somatic (body) cell, or 23 chromosomes in each germ cell (egg or sperm).
Chromosomes
Each somatic cell with a nucleus has 22 pairs of autosomes (the same in both sexes) and 1 pair of sex chromosomes. Females have two X sex chromosomes; males have one Y sex chromosome and one X sex chromosome. Normally, at conception, each individual receives one copy of each chromosome from the maternal egg cell (1 genome) and one copy of each chromosome from the paternal sperm cell (1 genome), for a total of 46 chromosomes (2 genomes). Karyotype is the term used to define the chromosomal complement of an individual, for example, 46, XY, as is determined by laboratory chromosome analysis. Each chromosome contains 800 to 3,000 genes.
Genes
Gene is the basic unit of inherited information. Each copy of the human genome in the nucleus has about 30,000 genes. Cells also have some nonnuclear genes located within the mitochondria within the cytoplasm. Alternate forms of a gene are termed alleles. For each gene, an individual receives one allele from each parent, and thus has two alleles for each gene on the autosomes and also on the X chromosomes in females. Males have only one X chromosome and, therefore, have only one allele for all genes on the X chromosome; they are hemizygous for all X-linked genes. At any autosomal locus, or gene site, an individual can have two identical alleles (homozygous) for that locus or can have two different alleles (heterozygous) at a particular locus. Genotype refers to the constitution of the genetic material of an individual; for practical purposes it is commonly used to address a specific gene pair. For example, the gene for sickle cell disease, the gene for cystic fibrosis, or the gene for familial polyposis. Phenotype refers to the physical or biochemical characteristics an individual manifests regarding expression of the presence of a particular feature, or set of features, associated with a particular gene. Each gene is composed of a unique sequence of DNA bases.
DNA: Nuclear and Mitochondrial
- Human DNA is a double-stranded helical structure comprised of four different bases, the sequence of which codes for the assembly of amino acids to make a protein—for example, an enzyme. These proteins are important for the following reasons:
- For body characteristics such as eye color.
- For biochemical processes such as the gene for the enzyme that digests phenylalanine.
- For body structure such as a collagen gene important to bone formation.
- For cellular functioning such as genes associated with the cell cycle.
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- The four DNA bases are adenine, guanine, cytosine, and thymine-A, G, C, and T.
- A change, or mutation, in the coding sequence, such as a duplicated or deleted region, or even a change in only one base, can alter the production or functioning of the gene or gene product, thus affecting cellular processes, growth, and development.
- DNA analysis can be done on almost any body tissue (blood, muscle, skin) using molecular techniques (not visible under a microscope) for mutation analysis of a specific gene with a known sequence or for DNA linkage of genetic markers associated with a particular gene.
Normal Cell Division
Mitosis occurs in all somatic cells, which, under normal circumstances, results in the formation of cells identical to the original cell with the same 46 chromosomes.
Meiosis, or reduction division, occurs in the germ cell line, resulting in gametes (egg and sperm cells) with only 23 chromosomes, one representative of each chromosome pair.
During the process of meiosis, parental homologous chromosomes (from the same pair) pair and undergo exchanges of genetic material, resulting in recombinations of alleles on a chromosome and thus variation in individuals from generation to generation.
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