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Concept and Basics of Genetics

Basics of Genetics by Mrs. Sambharam K.P ( Asst Prof) Lokmangal Science and Entrepreneurship College, Wadala. Concept and Basics of Genetics. Genetics. The process of transmission of characters from one generation to next generation is called the inheritance or heredity.

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Concept and Basics of Genetics

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  1. Basics of Geneticsby Mrs. Sambharam K.P( Asst Prof)Lokmangal Science and Entrepreneurship College, Wadala

  2. Concept and Basics of Genetics

  3. Genetics • The process of transmission of charactersfrom one generation to next generation is calledthe inheritance orheredity.

  4. Branches ofGenetics Cytogenetics Moleculargenetics Biochemicalgenetics Cancergenetics Immunogenetics Developmentalgenetics Behavioralgenetics Populationgenetics

  5. Importance of genetics inMedicine • ≈50% of first trimester abortion are dueto chromosomalabnormalities • Congenital malformation: ≈2-3% ofnewborns. • 2% infants are born with single genedisorder • More than half of childhood blindness, deafness and mental retardation are dueto geneticdisorders.

  6. GeneticInformation • Gene – basic unit ofgenetic information. Genes determinethe • inheritedcharacters. • Genome – the collectionof geneticinformation. • Chromosomes – storage unitsof • genes. • DNA- is a nucleic acidthat contains the geneticinstructions specifying thebiological development of all cellularforms oflife 5

  7. Chromosome LogicalStructure • Locus – location of agene/marker • on thechromosome. • Allele – one variant form of a gene/marker at a particularlocus. Locus1 Possible Alleles:A1,A2 Locus2 Possible Alleles:B1,B2,B3 6

  8. HumanGenome • Most humancells • contain 46chromosomes: • 2 sex chromosomes(X,Y): XY – inmales. • XX – infemales. • 22 pairs ofchromosomes named autosomes. 7

  9. Genotypes Phenotypes • At each locus (except for sex chromosomes) there are2genes. These constitute the individual’s genotype at thelocus. • The expression of a genotype is termed a phenotype. For example, hair color, weight, or the presence or absence of adisease. 8

  10. Genotypes Phenotypes(example) genotypes phenotypes • Eb- dominantallele. • Ew- recessiveallele. 9

  11. Dominant vs.Recessive A dominant allele is expressed even if itis paired with a recessiveallele. A recessive allele is only visible when paired with another recessiveallele. 10

  12. Mendel’s1stLaw Two members of a gene pair segregate from each otherinto the gametes, so half the gametes carry one member of the pairandtheotherhalfcarrytheothermemberofthepair. Y /y y /y Gamete production ally Gamete production ½y/y ½y ½Y/y ½Y 11

  13. Mendel’s2ndLaw • Different gene pairs assort independently in gameteformation. This “law” is true only insome cases. Gene pairs on SEPARATECHROMOSOMES assort independently atmeiosis. 12

  14. DNA • 1953 - James Watson, Francis Crick, Rosalind Franklin & MauriceWilkins • Lead to understanding of mutation and relationship between DNA and proteins at a molecularlevel • 1959 – “CentralDogma” • –DNARNAprotein

  15. GeneticConcepts condensedchromosome • Chromosome– • – double stranded DNA molecule packaged by histone & scaffoldproteins 30nmfiber nucleosome DNA doublehelix

  16. GeneticConcepts • Chromosomenumbers • Constant for anorganism • n - haploidnumber • 2n – diploidnumber • Karyotype

  17. GeneticConcepts Y

  18. GeneticConcepts • Chromosomenumbers • Each individual inherits 23 chromosomes from father and 23 frommother. • Humans: 2n= 46chromosomes • Humans 23 paternal, 23maternal • Humans n= • Each maternal & paternal pair represent homologous chromosomes - called homologs

  19. GeneticConcepts 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 9 10111213141516 17 18 19 20 21 (a) Chromosomal compositionfound in most female humancells (46chromosomes) 171819202122X (b) Chromosomalcomposition found in a human gamete (23chromosomes) 22 XX Diploid Haploid

  20. GeneticConcepts • HomologousChromosomes • Share centromereposition • Share overallsize • Contain identical gene sets at matching positions(loci) gene forcolor gene forshape

  21. GeneticConcepts • Gene – sequence of DNA which is transcribed intoRNA • – rRNA, tRNA ormRNA • Locus – the position on a chromosome ofa particular DNA sequence(gene) G Locus – gene forcolor W Locus – gene forshape

  22. GeneticConcepts • DNA ismutable • A variation in DNA sequence at a locus is called anallele • Diploid organisms contain 2 alleles of eachlocus (gene) • Alleles can be identical –homozygous • Alleles can be different –heterozygous • If only one allele is present –hemizygous • – Case in males for genes on X and Y chromosomes

  23. GeneticConcepts Allele – G vs g; W vsw At the G locus either the G or g allele may be present on a given homologue of a homologous pair ofchromosomes

  24. GeneticConcepts • Genome • Collectionofallgeneticmaterialoforganism • Genotype • Set ofalleles present in the genome of an organism • Phenotype • Result of GeneExpression • Genes (DNA) are transcribed intoRNA • mRNA is translated into protein, tRNA & rRNA workin translation process • Biochemical properties of proteins, tRNAs &rRNAs determine physical characteristics oforganism

  25. DNA Gene Expression Gene Transcription RNA (messengerRNA) Translation Protein (sequenceof aminoacids) Functioning of proteins withinliving cells influences an organism’straits.

  26. Mutation & PhenotypicVariation Pigmentationgene, darkallele Pigmentationgene, lightallele Transcription andtranslation (a) Molecularlevel Highly functional pigmentationenzyme Poorly functional pigmentationenzyme (b) Cellularlevel Pigment molecule Wingcells Lots ofpigmentmade Little pigmentmade

  27. MedicalGenetics • When studying rare disorders, 6 general patterns of inheritance areobserved: • Autosomalrecessive • Autosomaldominant • X-linked recessive • X-linked dominant • Codominant • Mitochondrial 26

  28. Medical Genetics(cont.) • Autosomalrecessive • The disease appears in male and female children of unaffectedparents. • e.g., cysticfibrosis 27

  29. Medical Genetics(cont.) • Autosomal dominant • Affected males and females appear ineach generation of the pedigree. • Affected mothers and fathers transmit the phenotype to bothsons anddaughters. • e.g., Huntingtondisease. 28

  30. Medical Genetics(cont.) • X-linkedrecessive • Many more males than females show thedisorder. • All the daughters ofan affected male are “carriers”. • None of the sons of an affected male show the disorder or arecarriers. • e.g.,hemophilia 29

  31. Medical Genetics(cont.) • X-linkeddominant • Affected males pass the disorder to all daughters but to none of theirsons. • Affected heterozygous females married to unaffected males pass the condition to half theirsons and daughters • e.g. fragile Xsyndrome 30

  32. Medical Genetics(cont.) • Codominantinheritance • Two differentversions • (alleles) of a gene can be expressed, and each version makes a slightly differentprotein • Both alleles influencethe • genetic trait or determine the characteristics of the genetic condition. • E.g. ABOlocus 31

  33. Medical Genetics(cont.) • Mitochondrialinheritance • This type ofinheritance applies to genes in mitochondrialDNA • Mitochondrial disorders can appear in every generation of a family and can affect both males and females, but fathers do not pass mitochondrial traits to theirchildren. • E.g. Leber's hereditary optic neuropathy(LHON) 32

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