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Genetics is the science that deals with the study of heredity and variation. what are genetics in science free ppt download
GENETICSWhat is Genetics?  It is the science that deals with the study of heredity and variation.  GENETICS came from the word gen, genetikos meaning generative and genesis meaning beginning. Heredity is a biological process where a parent passes certain genes onto their children or offspring.GENE ◉ Biological unit of heredity. ◉ Gene hold the information to build and maintain their cells and pass genetic traits to off springs. ◉ In cells, a gene is portion of DNA.Continued... Gene (DNA) RNA Formation Protein Formation Cell Structure Cell Enzymes Cell FunctionALLELE ◉ Is one member of a pair or series of different forms of a gene. ◉ Homozygous-an organism in which 2 copies of genes are identical i.e. have same alleles ◉ Heterozygous-an organism which has different alleles of the geneChromosomes ◉ Chromatin: DNA, RNA & proteins that make up chromosome ◉ Chromatids: One of the two identical parts of the chromosome. ◉ Centromere: The point where two chromatids attach ◉ 46 chromosomes, 22 pairs Autosomes and 1 pair Sex chromosomes.NUCLEOTIDE: group of molecules that when linked together, form the building blocks of DNA and RNA; composed of phosphate group, the bases: adenosine, cytosine, guanine and thymine and a pentose sugar. In case of RNA, thymine base is replaced by uracil. CODON: series of three adjacent bases in one polynucleotide chain of a DNA or RNA molecule which codes for a specific amino acid. GENETIC CODE: the sequence of nucleotides in a DNA or RNA molecule that determines the amino acid sequence in the synthesis of proteinsCauses of diseases • Accidents • Infections • Genetic diseases • Complex traitsGenetic diseases “ ◉ Inherited diseases ◉ Diseases due to mutations in somatic cells- cancerMutationsDefinition: Permanent changes in the DNA. Those that affect germ cells are transmitted to the progeny. Mutations in the somatic cells are not transferred to the progeny but are important in the causation of cancer and some congenital diseases.CAUSES OF MUTATIONS ◉ Chemicals  Nitrous acid Alkylating agents 5- bromouracil Antiviral drug iododeoxy uridine Benzpyrene in tobacco smoke ◉ X – rays & ultraviolet light ◉ Certain viruses such as bacterial virusTypes of MutationsPoint Mutation These affect a single amino acid or short sequence. These are also called single-base substitutions. • Missense mutations may change the code for a particular protein. • Nonsense mutations may make a change so that the whole chain stops. This mutation codes for a Stop codon.Frame shift Mutations Insertion or deletion of one or two base pairs alters the reading frame of the DNA strand.Snips or SNPs (Single nucleotide polymorphisms) These are the most common type of genetic variation among people. Each SNP represents a difference in a single DNA base for example nucleotide cytosine (C) replaced with the nucleotide thymine (T) in a certain stretch of DNA.Trinucleotide Repeat Mutations Set of genetic disorder caused by trinucleotide repeat in certain genes exceeding normal, stable threshold e.g. Fragile X Syndrome.Classification Of Genetic Diseases ◉ Single Gene Defects/Mendelian Disorders. ◉ Disorders with Multifactorial or Polygenic inheritance. ◉ Cytogenetic Disorders. ◉ Disorders showing atypical patterns of inheritance.Mendelian Disorders A genetic disease caused by a single mutation in the structure of DNA, which causes a single basic defect with pathologic consequencesPatterns Of Inheritance ◉ Autosomal Dominant. ◉ Autosomal Recessive. ◉ X-LinkedAutosomal Dominant Disorders ◉ The inherited gene is a dominant one. This means if a person carries even one copy of that gene, he or she is likely to develop the trait. ◉ In some dominant conditions, it is possible to inherit an altered gene without showing any signs of the condition, i.e. the gene is not fully penetrant. ◉ Examples of genetic conditions that are inherited in a dominant way are Huntington’s disease and Neurofibromatosis type 1 (NF1).Autosomal Recessive Disorders ◉ With recessive genes, it is only if someone inherits two altered copies of the same gene from each of their parents, they are likely to be expressed. ◉ For example, inheritance of thalassemia and cystic fibrosis occurs in an autosomal recessive pattern. If both parents carry the faulty gene on one of their alleles they are likely pass on their defective gene in only 25% of their offspring. X-Linked Disorders ◉ When an altered gene is located on the X chromosome (one of the sex chromosomes) rather than on one of the autosomes. ◉ If this gene is a recessive one then a woman who carries an altered copy will either have no signs of the condition caused by that gene or will have minor signs of the condition. ◉ She is said to be a carrier of that X-linked condition.DISORDERS WITH MULTIFACTORIAL (POLYGENIC)INHERITANCE ◉ Involved in many physiologic characteristics of humans e.g. height, weight, hair color ◉ Defined as one governed by additive effect of two or more genes of small effect but conditioned by environmental, non genetic influences ◉ The disorder becomes manifested only when a certain number of effector genes, as well as conditioning environmental influences are involved. ◉ Rate of recurrence is 2 to 7%COMMON DISEASES ASSOCIATED • Diabetes mellitus • Hypertension • Gout • Cleft lip and palate • Schizophrenia • Bipolar disorder • Congenital heart disease • Skeletal abnormalities • Neural tube defects • Coronary artery diseaseCytogenetic DisordersKARYOTYPING ◉ Basic tool of cytogeneticist ◉ Karyotype is a photographic representation in which chromosomes are arranged in order of decreasing length ◉ Giemsa stain (G banding) technique—each chromosome can be seen to possess a distinctive pattern of alternating light and dark bands of variable widthsContinued.. ◉ Cytogenetic disorders may result from structural or numeric abnormalities of chromosomes ◉ It may affects autosomes or sex chromosomesNumeric Abnormalities ◉ Normal Chromosomal number is 46. (2n=46). This is called euploid state. (Exact multiple of haploid number). ◉Polyploidy: posession of more than two sets of homologous chromosomes. Chromosomal numbers like 3n or 4n. (Incompatible with life); generally results in spontaneous abortion ◉Aneuploidy: Any Chromosomal number that is not an exact multiple of haploid number . E.g. 47 or 45.Aneuploidy ◉ Most common cause is nondisjunction of either a pair of homologous chromosomes during meiosis I or failure of sister chromatids to separate during meiosis II. ◉The resultant gamete will have either one less chromosome or one extra chromosome.◉ Fertilization of such gamete will result in zygote being either trisomic ( 2n+1 ) or monosomic ( 2n-1 ). ◉ Monosomy in autosomes is incompatible with life. Trisomy of certain autosomes and monosomy of sex chromosomes is compatible with life.Structural Abnormalities ◉ Usually result from chromosomal breakage, resulting in loss or rearrangement of genetic material. ◉ Patterns of breakage: • Translocation. • Isochromosomes. • Deletion. • Inversions. • Ring Chromosomes.TRANSLOCATION ◉ Transfer of a part of one chromosome to another chromosome ◉ Translocations are indicated by t E.g. 46,XX,t(2;5)(q31;p14) ◉ Balanced reciprocal translocation is not harmful to the carrier, however during gametogenesis, abnormal gametes are formed, resulting in abnormal zygotes ◉ Centric fusion type or robertsonianTranslocation: The breaks occur close to the centromere, affecting the short arms of both chromosomes Transfer of the chromosome leads to one very large and one extremely small chromosome The short fragments are lost, and the carrier has 45 chromosomes Such loss is compatible with survival However, during gametogenesis difficulties ariseISOCHROMOSOMES ◉ Result when one arm of a chromosome is lost and the remaining arm is duplicated, resulting in a chromosome consisting of two short arms only or of two long arms. DELETION ◉ Loss of a portion of chromosome ◉ This can be terminal (close to the end of the chromosome on the long arm or the short arm), or it can be interstitial (within the long arm or the short arm). ◉ A ring chromosome is a variant of deletion. It occurs when break occurs at both the ends of chromosome with fusion of the damaged ends.INVERSIONS ◉ Occur when there are two breaks within a single chromosome with inverted reincorporation of the segment. ◉ Since there is no loss or gain of chromosomal material, inversion carriers are normal. ◉ An inversion is paracentric if the inverted segment is on the long arm or the short arm. ◉ The inversion is pericentric if breaks occur on both the short arm and the long arm.APPLICATION OF GENETICS 1. Field of Medicine 2. Agriculture/Food Production/Industry 3. Legal Application 4. Genetic Counseling 5. Genetic CodeMedical research and genetic engineering  Medical genetics includes studies of populations that look at the effects of genetic changes, mutations and variations on human health and disease. Principles of genetic linkage and genetic pedigree charts may help determine the location on the genome associated with the disease.  Mendelian randomization helps to look for locations in the genome that are associated with diseases. This is a technique useful for multigenic traits not clearly defined by a single gene.Continued…  After a gene is identified to be associated with a disease further research is often done on the same gene in the experimental models. Genotypes are established to pinpoint the exact location of the gene.DNA Research ◉ DNA is used for research in the laboratory. Restriction enzymes are a commonly used enzyme that cut DNA at specific sequences. This is then visualized through the use of gel electrophoresis. The DNA can then be amplified, modified or cut into pieces for research using sophisticated technology. DNA can be amplified using a procedure called the polymerase chain reaction (PCR). ◉ DNA may be sequenced and this allows researchers to determine the sequence of nucleotides in fragments of DNA. This is progressively becoming easier and less expensive. This can be used in DNA fingerprinting or RFLP (Restriction Fragment Length Polymerization).Continued… ◉ DNA may be sequenced and this allows researchers to determine the sequence of nucleotides in fragments of DNA. This is progressively becoming easier and less expensive. This can be used in DNA fingerprinting or RFLP (Restriction Fragment Length Polymerization).USE CHARTS TO EXPLAIN YOUR IDEASTHANKS Any questions? You can find us at
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