Genetics: From Classical to Molecular - A Historical Overview - Prof. Eric P. Beers, Study notes of Genetics

Download Genetics: From Classical to Molecular - A Historical Overview - Prof. Eric P. Beers and more Study notes Genetics in PDF only on Docsity! Genetics 3rd Lecture Dr. E. H. Shokraii Genetics Genetics begin in mid 19th century Classical genetics – Mendelian genetics (all on pea plants) Early 20th century chromosomal basic of genetics – Fleming 1878, 1912 Morgan & Drosophila genetics 1930s Mid 20th century discovery of DNA and from gene to protein Late 60s and early 70s genetic code cracked gene  protein 1 gene  1 protein Late 70s  molecular genetics, bacterial (E. coli) genetics Kornberg  viruses, using DNA-polymerase  synthetic virus, in-vitro virus Aug 2000, human genome sequenced,  2006 detail completed 21st century, May 2nd 2010  1st bacteria made by man? (in vitro) Basic principles of heredity 1st experiment  Monohybrid cross round seed X wrinkled seed 1st generation (F1) all seed were round 2nd generation (F2) ¾ round, ¼ wrinkle 5474 round, 1850 wrinkled  Genes do not Vanish !!  Genes do not Blend flower color Reciprocal cross  same result Conclusion  It doesn't matter whether the gene is from the father or the mother Basic principles of heredity Gene  a genetic factor (DNA region)  Genes exist in different variation called alleles  Genes exist in certain location called locus  Different alleles occupy same locus on homologous chromosomes Genotype  genetic make-up sets of alleles in an individual Phenotype  physical appearance or manifestation of certain character Homozygote  having same (2) alleles at a locus Heterozygote  having different alleles at a locus  Monohybrid  1 gene involved  Dihybrid  2 genes involved  Reciprocal cross. Does the gene inheritance varies according to it’s own origin? (paternal or maternal)  Test cross identifies whether homozygotes or heterozygotes Homozygote  AA X aa  all Aa (shown dominance) Heterozygote  Aa X aa  ½ Aa & ½ aa Basic principles of heredity Cross unknown genotype with known homozygote recessive  Incomplete dominance  Codominance vs. Dominant & Recessive Genes  Dominant / Recessive Complete dominance vs. Incomplete dominance Co-dominance !! Eugenics  Artificial selection in Man (horse) to improve favorable traits (Galton’s idea, Nazzi)  Euphenics  Medical & genetic intervention dealing with reducing the impact of bad gene Multiple Loci cross Dihybrid cross – round yellow, wrinkled green 4 X 4 = 16 F1 RRYY X rryy  all RrYy F2  ration of 9, 3, 3, 1 / 16 RY, Ry, rY, ry Result of segregation of alleles & independent assortment of alleles (4 different gametes) Note; principle of independent assortment have conflict in case; alleles are not located on different chromosomes or either no crossing over. As genes located on same chromosome, cannot assort independently unless have 100% crossing over  Branched diagram more convenient for Tri, Tetra, Penta hybrids Consider a cross between AaBbCcDdEe X AaBbCcDdEe What is the probability of having combination of aabbccddee?!  Using punnett square  takes long time but can calculate using single cross for each trait Aa X Aa or Bb X Bb etc will be ¼ aa and ¼ bb Thus ¼ X ¼ X ¼ X ¼ X ¼ = 1/1024 This is the probability of having aaqbbccddee. One out of 1024 Observed and expected ratio may not be same as possibility of chance exist. Due to interaction of other genes Penetrance & Expressibility ; ex. Polydactyli, the gene express in male stronger than female Presence of a gene does not guarantee its expression  Chi square Monohybrid AA X aa  Aa F1 Aa X Aa  AA, Aa(Aa and aA), aa F2 4 combination 1 2 1  ratio Dihybid AABB X aabb  AaBb F1 AaBb X AaBb  16 combination F2 Ratio 9/16  show both dominance 3/16  only 1 dominance 3/16  only 1 dominance 1/16  all recessive trait Incomplete dominance, Codominance  F1 F2  separation (Independent) of alleles  Show genes are not blending!! hi > P generation Homozygous Homozygous round seeds wrinkled seeds o<«® WC eet rode tutti \' |Cross| (§; generation or ee Cae | Self-fertilized 30:90 Cit eMe teers} Coe tsit [intercross] y v (FS generation Anthers SS Fraction of progeny seeds 5474 Round seeds -) 3/4 Round 1850 Wrinkled seeds Y 1/4 Wrinkled N J Pierce, Genetics: A Conceptual Approach Figure 3.3 © 2003 by W. H. Freeman and Company 7-014 (a) No crossing over Crossing over (b) Pierce, Genetics: A Conceptual Approach Figure 3.5 © 2003 by W. H. Freeman and Company F015 A testcross (Fig 13.6) Copyright © The Benjamin /Cummings Publishing Company, Inc, from Campbell's BIOLOGY, Third Edition. Fig. 20-14 The Meiotic Basis for Mendel’s Law of Segregation Possible haploid gametes. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings. Recombination due to crossing over (Figure 14.7) bt vg asp aa(—-— s 6 b vg Wild ty; Black-vestigial Bay SOTO: oe wings | + net} + +H eine bT x by bF us b x eae ae e=a=Dp ess Sep a= b vg b vg b vg b ug b vg Wild type Black- Gray- Black- . vestigial vestigial normal §. 50% 965 944 206 185 wy ° \ u J Parental types Recombinants Recombination frequency = ot ee X 100 = 17% (a) 2300 total offspring bt ugt Ova (b) oe s¢ Copyright © The Benjamin/Cummings Publishing Company, Inc., from Campbell's BIOLOGY, Third Edition. Fig. 20-15 The Meiotic Basis for Mendel’s Law of Independent Assortment eanees ee us (YyRr) Prophase | diploid cell from a plant oe eas Possible haploid gametes Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings. x , ae ww. ‘Gross 6 a a be R Re Rr Yy Cc (SEAM © yg eX Yo BRM Rr Expected proportions Expected proportions Expected proportions proportions for for first character for second character for third character aT three characters ¥R_ Round () arr Wrinkled GE) See '¥4 R_ Round © Ya rr Wrinkied > Pierce, Genetics: A Conceptual Approach Figure 3.14 © 2003 by W. H. Freeman and Company 7-018 Independent assortment and variations in the a B ox of bud Y4Bb (Figure 13.9) Yabbe (a) Phenotype and genotype Phenotype Green Yellow Genotype YB Y_bb (b) Cross sections of feathers | Yellow Melanin No Melanin Yellow No pigment granules pigment granules pigment melanin pigment melanin Cet Sea Phenotypic ratioof ~ [9Green | MM [| svetlow | [__1 white offspring Copyright © The Benjamin /Cummings Publishing Company, Inc., from Campbell’s BIOLOGY, Third Edition.