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Human Genetics Human Genetics Is the Study of Inheritance As It Occurs in Human Beings

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Human Genetics Human Genetics Is the Study of Inheritance As It Occurs in Human Beings 3rd stage Human Genetic Human genetics Human genetics is the study of inheritance as it occurs in human beings. Human genetics encompasses a variety of overlapping fields including: classical genetics, cytogenetics, molecular genetics, biochemical genetics, genomics, population genetics, developmental genetics, clinical genetics, and genetic counseling. Or The relationship between natural DNA sequence variation(s) and human phenotypic traits The process of transmission of characters from one generation to the next is called Inheritance or heredity. The characters are determined by Genes which are fundamental units of inheritance. Each species of living organism has a unique set of inherited characteristics that makes it different from other species. Organisms that are members of the same species usually resemble one another, with some notable exceptions differences between males and females. For example, it is easy to distinguish a human being from a chimpanzee or a gorilla. A human being (Homo sapiens) stands upright and has long legs, relatively little body hair, a large brain, and a flat face with a prominent nose, jutting chin, distinct lips, and small teeth. All of these traits are inherited. But human beings are by no means identical. Many traits, or observable characteristics, differ from one person to another. There is a great deal of variation in hair color, eye color, skin color, height, weight, personality traits, and other characteristics. 1 3rd stage Human Genetic Some human traits are transmitted biologically, others culturally. The color of our eyes results from biological inheritance, but the native language we learned as a child results from cultural inheritance. Many traits are influenced jointly by biological inheritance and environmental factors. For example, weight. Branches of Genetics Human genetics can now be divided into several branches few important sub disciplines are as under: 1. Cytogenetics : it deals with how the chromosomes relate to cell behavior, particularly to their behavior during mitosis and meiosis. 2. Molecular genetics is the field that studies the chemical structure and function of genes at a molecular level and thus employs methods of both molecular biology and genetics. 3. Biochemical Genetics the study of the fundamental relationships between genes, protein, and metabolism. This involves the study of the cause of many specific heritable diseases. 4. Cancer genetics is the understanding of the genetic processes underlying the actual disease occurrence. This understanding plays a significant role in early detection, therapy, prevention, and prognosis. 5. Immunogenetics: is the branch of medical genetics that explores the relationship between the immune system and genetics. 6. Population genetics : is a subfield of genetics that deals with the laws on genetics acting on human population .is the study of changes in gene frequencies in population of organisms and the effects of such changes on evolution and adaptation. 2 3rd stage Human Genetic 7. behavioral genetics: it deals with the influence of geneson behavior of an individuals. Genetics is the study of biologically inherited traits, including traits that are influenced in part by the environment. Genes is the elements of heredity that are transmitted from parents to offspring in reproduction to determine the Inherited traits . The existence of genes and the rules governing their transmission from generation to generation were first articulated by Gregor Mendel in 1866. Mendel’s formulation of inheritance was in terms of the abstract rules by which hereditary elements (he called them “factors”) are transmitted from parents to offspring. The foundation of genetics as a molecular science dates back to 1869, just three years after Mendel reported his experiments. It was in 1869 that Friedrich Miescher discovered a new type of weak acid, abundant in the nuclei of white blood cells. Miescher’s weak acid turned out to be the chemical substance we now call DNA (deoxyribonucleic acid). For many years the biological function of DNA was unknown, and no role in heredity was ascribed to it. The cell nucleus plays a key role in inheritance was recognized in the 1870s by the observation that the nuclei of male and female reproductive cells undergo fusion in the process of fertilization. Soon thereafter, chromosomes were first observed inside the nucleus as thread-like 3 3rd stage Human Genetic objects that become visible in the light microscope when the cell is stained with certain dyes. The number of chromosomes in each cell may differ among biological species, but the number of chromosomes is always constant within the cells of any particular species (except sex cells). These features of chromosomes were well understood by about 1900, and they made it seem likely that chromosomes were the carriers of the genes. What are chromosomes made of? Each chromosome is made up of two strands of deoxyribonucleic acid (DNA) in a double helix arrangement 2 meters of DNA per cell! 4 3rd stage Human Genetic Cell division Cell divisions the process by which cells produce new cells. All cells are derived from pre-existing cells. Cell division consists of four steps: A signal to divide DNA replication DNA segregation (separation) Cytokinesis – dividing the cytoplasm. Types of Cell Division • Binary Fission – The process of cell division in prokaryotes, which simply divides the cells contents. • Mitosis • Meiosis 5 3rd stage Human Genetic Cell division in Prokaryotes Eukaryotes 1. Always single celled Often multi cellular 2. Usually only one chromosome per cell Several chromosomes per cell 3. Usually a circular chromosome Linear chromosomes 4. One origin of replication Several origins of replication per chromosome 5. Divide as long as the conditions are Cell division is carefully restricted (in favorable particular in multicellular organisms) Basic definitions: gene - basic unit of heredity; codes for a specific trait genome - the total hereditary endowment of DNA of a cell or organism somatic cell - all body cells except reproductive cells gamete - reproductive cells (i.e. sperm & eggs) chromosome - elongate cellular structure composed of DNA and protein - they are the vehicles which carry DNA in cells diploid (2n) - cellular condition where each chromosome type is represented by two homologous chromosomes haploid (n) - cellular condition where each chromosome type is represented by only one chromosome homologous chromosome - chromosome of the same size and shape which carry the same type of genes chromatid - one of two duplicated chromosomes connected at the centromere centromere - region of chromosome where microtubules attach during mitosis and meiosis 6 3rd stage Human Genetic Chromosome structure Composed of DNA and protein (histones) all tightly wrapped up in one package Duplicated chromosomes are connected by a centromere. Supercoiling Eukaryotic chromosomes consist of DNA wrapped around histone proteins, this forms the basic structure of the nucleosome, which is packed together to form chromatin (in a 'beads on a string' arrangement) If the DNA is twisted in the direction of the helix, this is positive supercoiling, and the bases are held more tightly together. If they are twisted in the opposite direction, this is negative supercoiling, and the bases come apart more easily. 7 3rd stage Human Genetic Chromatin is a mass of genetic material composed of DNA and proteins that condenses to form chromosomes during eukaryotic cell The primary functions of chromatin are: 1) to package DNA into a smaller volume to fit in the cell 2) to reinforce the DNA macromolecule to allow mitosis 3) to prevent DNA damage. 4) to control gene expression and DNA replication. Arrangement of DNA into Chromosomes 8 3rd stage Human Genetic Example - an organism is 2n = 4. Chromosomes 1 & 2 are homologous chromosomes Chromosomes 3 & 4 are homologous chromosomes Chromosomes 1 & 3 came from the mother Chromosomes 2 & 4 came from the father The cell cycle Actively dividing eukaryote cells pass through a series of stages known collectively as the cell cycle: two gap phases (G1 and G2); an S (for synthesis) phase, in which the genetic material is duplicated; and an M phase, in which mitosis partitions the genetic material and the cell divides. 1. G1 phase. Metabolic changes prepare the cell for division 2. S phase. DNA synthesis replicates the genetic material. Each chromosome now consists of two sister chromatids. 3. G2 phase. Metabolic changes assemble the cytoplasmic materials necessary for mitosis and cytokinesis. 4. M phase. A nuclear division (mitosis) followed by a cell division (cytokinesis). The period between mitotic divisions - that is, G1, S and G2 - is known as interphase. 9 3rd stage Human Genetic Mitosis It is the process of somatic cell division that result in the formation of two daughter cells that are genetically identical to each other and the parent cell. Mitosis is used by single-celled organisms to reproduce. The replicated chromosomes are attached to a 'mitotic apparatus' that aligns them and then separates the sister chromatids to produce an even partitioning of the genetic material. This separation of the genetic material in a mitotic nuclear division (or karyokinesis) is followed by a separation of the cell cytoplasm in a cellular division (or cytokinesis) to produce two daughter cells. Mitosis, although a continuous process, is conventionally divided into five stages: prophase, prometaphase, metaphase, anaphase and telophase. Role of
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