BIOLOVE         GENETICSM.I/ASASI/2013      Page 1
Genes    –    Basic unit of inheritance or information about specific traits    –    Located on chromosomes    –    For ex...
Homozygous dominant   –   PP, YY, TT, MM   –   Combination of two same capital letterHomozygous recessive   –   pp, tt, mm...
Why he chose pea plant to study about inheritance of traits?    •   Advantages of pea plants for genetic study:           ...
•   When Mendel crossed contrasting, true-breeding white and purple flowered pea plants, all       of the F1 hybrids were ...
Law of segregationTwo alleles of a gene seperate or segregate from each other into different gametes during theformation o...
•    Crossing two true-breeding parents differing in two characters produces dihybrids in the F1         generation, heter...
•   Using a dihybrid cross, Mendel developed the law of independent assortment   •   The law of independent assortment sta...
Extension to Mendel’s Genetics   •   Complete dominance occurs when phenotypes of the heterozygote and dominant       homo...
Multiple Alleles   •   Most genes exist in populations in more       than two allelic forms   •   For example, the four ph...
Polygenic Inheritance   •   Quantitative characters are       those that vary in the population       along a continuum   ...
Useful Diagram To help youM.I/ASASI/2013               Page 12
M.I/ASASI/2013   Page 13
Steps to write genetic diagramStep 1: Cross the parents                                           BbCc x BbCcStep 2: Obtai...
If the genotype exist as BBCC,Then the gamete will be BC and BC. But we will take one only out of two which we’ll write BC...
•   The nitrogenous bases           –   Are paired in specific combinations: adenine with thymine, and cytosine with      ...
•   In DNA replication           –   The parent molecule unwinds, and two new daughter strands are built based on         ...
•   The copying of DNA          –   Is remarkable in its speed and accuracy   •   More than a dozen enzymes and other prot...
•   The replication of a DNA molecule            –   Begins at special sites called origins of replication, where the two ...
Primase will synthesize RNA primerRNAase H removes the RNA primerDNA polymerase I replace the RNA primer with DNA nucleoti...
Synthesis of leading and lagging strands during DNA replication   •    DNA polymerases cannot initiate the synthesis of a ...
6. RNAase H removes the primer                 from 5’ end of second fragment. DNA                 polymerase I replace th...
Protein SynthesisThe two stgaes of protein synthesis is Transcription and Translation    •   Transcription            –   ...
•   Genetic information            –   Is encoded as a sequence of nonoverlapping base triplets, or codons    •   How many...
2. Redundant:    –   More than one codon for an amino acids    3. Unambigous    –   One codon can only specify an amino ac...
Initiation        -    RNA polymerase bind to promoter        -    DNA double helix unwind        -    RNA polymerase tran...
-      TF binds to DNA strand      -      RNA polymerase II bind to DNA at TF      -      TF + RNA polymerase + TATA box =...
-   RNA polymerase elongate transcription from 5’ to 3’       -   Transcribed DNA will reform the double helix       -   N...
Why mRNA ends need to be altered?       -   Protects the RNA from degradation       -   Helps the ribosome to attach to th...
Translation    •   A cell translates an mRNA message into protein              –   With the help of transfer RNA (tRNA) an...
•   Ribosomes            –   Facilitate the specific coupling                of tRNA anticodons with mRNA                c...
Initiation of TranslationElongation    •   In the elongation stage of translation             –   Amino acids are added on...
Termination   •   The final stage of translation is termination           –   When the ribosome reaches a stop codon in th...
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Biolove genetics part 1

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Biolove genetics part 1

  1. 1. BIOLOVE GENETICSM.I/ASASI/2013 Page 1
  2. 2. Genes – Basic unit of inheritance or information about specific traits – Located on chromosomes – For example, the height of pea plant is determined by a geneLocus – Location in chromosomes where genes are locatedAllele – If the a gene give the height characteristics, – Allele determine either it is tall or short – So, Allele is the variant of the same geneAnother example – Gene: Hair colour  Allele: Black or blonde – Gene: Fur colour  Allele: White or yellowDominant Allele – Presented by capital letter. Example: (T, P, B, A) – Will show the effects on organismRecessive allele – Presented by small letter. – No effects on organism if paired with dominant allele For example: If P is for blue colour, and p is for red colour Pp = blue colour pp = red colour pp PpHomozygous – The same letter. Example: tt, YY, NN – Can be either homozygous dominant or recessiveM.I/ASASI/2013 Page 2
  3. 3. Homozygous dominant – PP, YY, TT, MM – Combination of two same capital letterHomozygous recessive – pp, tt, mm, nn – combination of two same small letterHeterozygous – one small letter and one capital letter – Example: Tt, Mn, Hh, RrGenotype – Genetic composition of an organism which is not visible externally – The genotype of plant is represented by the allele present – Hence, if P is allele for tall plant, all tall plants will have the genotype of Pp or PPPhenotype – External appearance or observable features – Example: Colour, size, structureHistory of genetisWe have to know Mendel, the father of modern geneticsWhat he do? – He study the inheritance of traits in pea plantsWho is he? – An Austrian priestM.I/ASASI/2013 Page 3
  4. 4. Why he chose pea plant to study about inheritance of traits? • Advantages of pea plants for genetic study: – There are many varieties with distinct heritable features, or characters (such as flower color); character variants (such as purple or white flowers) are called traits – Mating of plants can be controlled – Each pea plant has sperm-producing organs (stamens) and egg-producing organs (carpels) – Cross-pollination (fertilization between different plants) can be achieved by dusting one plant with pollen from another • Mendel chose to track only those characters that varied in an either-or manner • He also used varieties that were true-breeding (plants that produce offspring of the same variety when they self-pollinate)Inheritance of single trait is called as monohybrid • In a typical experiment, Mendel mated two contrasting, true-breeding varieties, a process called hybridization • The true-breeding parents are the P1 or parental generation • The hybrid offspring of the P generation are called the F1 generation or first filial generation • When F1 individuals self-pollinate, the F2 generation or second filial generation is producedM.I/ASASI/2013 Page 4
  5. 5. • When Mendel crossed contrasting, true-breeding white and purple flowered pea plants, all of the F1 hybrids were purple • When Mendel crossed the F1 hybrids, many of the F2 plants had purple flowers, but some had white • Mendel discovered a ratio of about three to one, purple to white flowers, in the F2 generation Fertilized among F1 F1 x F1 If the dominant or recessive trait is not mentioned in the question, please refer to this table.M.I/ASASI/2013 Page 5
  6. 6. Law of segregationTwo alleles of a gene seperate or segregate from each other into different gametes during theformation of gametes. • Thus, an egg or a sperm gets only one of the two alleles that are present in the somatic cells of an organism • This segregation of alleles corresponds to the distribution of homologous chromosomes to different gametes in meiosis Allele in a pair Separate/segregate Into different gamete • The possible combinations of sperm and egg can be shown using a Punnett square, a diagram for predicting the results of a genetic cross between individuals of known genetic makeup Gametes must be circled This is Monohybrid crossM.I/ASASI/2013 Page 6
  7. 7. • Crossing two true-breeding parents differing in two characters produces dihybrids in the F1 generation, heterozygous for both characters (YyRr) • A dihybrid cross, a cross between F1 dihybrids, can determine whether two characters are transmitted to offspring as a package or independentlyThis is not valid for dihybrid crossM.I/ASASI/2013 Page 7
  8. 8. • Using a dihybrid cross, Mendel developed the law of independent assortment • The law of independent assortment states that each pair of alleles segregates independently of each other pair of alleles during gamete formation • Strictly speaking, this law applies only to genes on different, nonhomologous chromosomes • Genes located near each other on the same chromosome tend to be inherited together • Mendel’s laws of segregation and independent assortment reflect the rules of probability • When tossing a coin, the outcome of one toss has no impact on the outcome of the next toss • In the same way, the alleles of one gene segregate into gametes independently of another gene’s alleles • The multiplication rule states that the probability that two or more independent events will occur together is the product of their individual probabilities • Probability in an F1 monohybrid cross can be determined using the multiplication rule • Segregation in a heterozygous plant is like flipping a coin: Each gamete has a chance of carrying the dominant allele and a chance of carrying the recessive alleleM.I/ASASI/2013 Page 8
  9. 9. Extension to Mendel’s Genetics • Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical Heterozygote = Pp Both has identical phenotype which is Homozygote dominant = PP purple colour • In incomplete dominance, the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties – For example: TT x YY GG x HH OR GH TY – The third organism display both appearance from parents It is not necessary to write the capital letter C when writing the genetic diagram • In codominance, two dominant alleles affect the phenotype in separate, distinguishable ways - Example provided in the summary table of degree of dominance at page 11M.I/ASASI/2013 Page 9
  10. 10. Multiple Alleles • Most genes exist in populations in more than two allelic forms • For example, the four phenotypes of the ABO blood group in humans are determined by three alleles for the enzyme (I) that attaches A or B carbohydrates to red blood cells: IA, IB, and i. • The enzyme encoded by the IA allele adds the A carbohydrate, whereas the enzyme encoded by the IB allele adds the B carbohydrate; the enzyme encoded by the i allele adds neitherEpistasis – In Epistasis, a gene at one locus alters the phenotypic expression of a gene at a second locus – For example, in mice and many other mammals, coat color depends on two genes – One gene determines the pigment color (with alleles B for black and b for brown) – The other gene (with alleles C for color and c for no color) determines whether the pigment will be deposited in the hair If at least one allele C is exist, the fur will have either black or brown colour If no allele C exist but only allele c is exist, for example BBcc, the fur will have no colour. Fur will be white. Briefly, if no dominant allele for colour, the fur will have no colourM.I/ASASI/2013 Page 10
  11. 11. Polygenic Inheritance • Quantitative characters are those that vary in the population along a continuum • Quantitative variation usually indicates polygenic inheritance, an additive effect of two or more genes on a single phenotype • Skin color in humans is an example of polygenic inheritance • More than two genes will affect the skin colourTestcross – Crossing an unkown genotype with a homozygous recessive Homozygous recessive ________ x rr unknownSummary of Extension to Mendelian GeneticsM.I/ASASI/2013 Page 11
  12. 12. Useful Diagram To help youM.I/ASASI/2013 Page 12
  13. 13. M.I/ASASI/2013 Page 13
  14. 14. Steps to write genetic diagramStep 1: Cross the parents BbCc x BbCcStep 2: Obtain the gamete – From BbCc, we make the gamete by using the arrows BbCc BC Bc bC bc – OR we can use numbering system 2 1 4 BbCc 3 Number the letter as shown above Then, combine the letter Note that number 1 and 2 1 + 3 = BCBC cannot cross together. Same goes to number 3 1 + 4 = Bc and 4 Gamete 2 + 3 = bC 2 + 4 = bcM.I/ASASI/2013 Page 14
  15. 15. If the genotype exist as BBCC,Then the gamete will be BC and BC. But we will take one only out of two which we’ll write BC onlyinstead of BC and BC because it is the same.Step 3: Draw a punnet square to obtain the F1 BC Bc bC bc BBCC BBCc BbCC BbCc BC BBCc BBcc BbCc Bbcc Bc BbCc BbCc bbCC bbCc bC BbCc Bbcc bbCc bbcc bcStep 4: Write the Genotypic ratio and phenotypic ratioGenotypic ratio: ________________________________________Phenotypic ratio: _______________________________________DNA – Is a polymer of nucleotides, each consisting of three components: a nitrogenous base, a sugar, and a phosphate groupM.I/ASASI/2013 Page 15
  16. 16. • The nitrogenous bases – Are paired in specific combinations: adenine with thymine, and cytosine with guanine • Each base pair forms a different number of hydrogen bonds – Adenine and thymine form two bonds, cytosine and guanine form three bonds • DNA – Was composed of two antiparallel sugar-phosphate backbones, with the nitrogenous bases paired in the molecule’s interior – Twisted into helical shapeDifferences between DNA and RNA Aspect DNA RNA Sugar Deoxyribose Ribose Bases A-T, C-G U-A, C-G – The base thymine, T is replaced by Uracil, U Strand Double SingleDNA Replication – Copying the double strand DNA – Genetic material is passed down to daughter cells – Happens before cell divisionIn prokaryotes happen through the interval between cell divisionsEukaryotes happens during the S phaseM.I/ASASI/2013 Page 16
  17. 17. • In DNA replication – The parent molecule unwinds, and two new daughter strands are built based on base-pairing rulesModel of DNA replicationThe Semiconservative model was then accepted when Meselson and Stahl carried out an experimentto prove it. • Experiments performed by Meselson and Stahl – Supported the semiconservative model of DNA replicationM.I/ASASI/2013 Page 17
  18. 18. • The copying of DNA – Is remarkable in its speed and accuracy • More than a dozen enzymes and other proteins – Participate in DNA replicationM.I/ASASI/2013 Page 18
  19. 19. • The replication of a DNA molecule – Begins at special sites called origins of replication, where the two strands are separated • A eukaryotic chromosome – May have hundreds or even thousands of replication originsReplication occurs in the direction from 5’ to 3’ – Continuous repliation on 3’ to 5’ template – Discontinuous on 5’ to 3’ template. Replication form short segments  DNA replication starts when the DNA is unwind by DNA Helicase at area known as replication fork  More replication bubbles – faster the process of copying the DNA strand  Once Helicase has unwind the strand, single strand binding protein will bind to the single strand DNA and stabilize it.Here are the summary of action by the moleculesM.I/ASASI/2013 Page 19
  20. 20. Primase will synthesize RNA primerRNAase H removes the RNA primerDNA polymerase I replace the RNA primer with DNA nucleotidesRNA primer is the start point for DNA polymerase • Elongation of new DNA at a replication fork – Is catalyzed by enzymes called DNA polymerases, which add nucleotides to the 3 end of a growing strand DNA polymerase I • DNA polymerase I add nucleotides – Only to the free 3 end of a growing strand • Along one template strand of DNA, the leading strand – DNA polymerase III can synthesize a complementary strand continuously, moving toward the replication fork • To elongate the other new strand of DNA, the lagging strand – DNA polymerase III must work in the direction away from the replication fork • The lagging strand – Is synthesized as a series of segments called Okazaki fragments, which are then joined together by DNA ligaseM.I/ASASI/2013 Page 20
  21. 21. Synthesis of leading and lagging strands during DNA replication • DNA polymerases cannot initiate the synthesis of a polynucleotide – They can only add nucleotides to the 3 end RNAase H remove the RNA primer Figure 16.15 showing Replication in Lagging strandsM.I/ASASI/2013 Page 21
  22. 22. 6. RNAase H removes the primer from 5’ end of second fragment. DNA polymerase I replace the primer with DNA nucleotides that it adds one by one to the 3’ end of the 3rd fragment. The replacement of the last RNA nucleotide with DNA leaves the sugar phosphate backbone with a free 3’ endM.I/ASASI/2013 Page 22
  23. 23. Protein SynthesisThe two stgaes of protein synthesis is Transcription and Translation • Transcription – Is the synthesis of RNA under the direction of DNA – Produces messenger RNA (mRNA) • Translation – Is the actual synthesis of a polypeptide, which occurs under the direction of mRNA – Occurs on ribosomes • In prokaryotes – Transcription and translation occur together • In eukaryotes – RNA transcripts are modified before becoming true mRNAM.I/ASASI/2013 Page 23
  24. 24. • Genetic information – Is encoded as a sequence of nonoverlapping base triplets, or codons • How many bases correspond to an amino acid? – 3 base will form codon which will specify amino acidEach codon consist of three nucleotides (base)During transcription – The gene determines the sequence of bases along the length of an mRNA molecule4 characteristics of Genetic code 1. Triplet: – 3 nucleotides(codon) will specify one amino acid  Each amino acid may have more than one codon. But one codon only specify for an amino acid – Overall 61 codons + 3 stop codons – AUG is the start codon (AUG codes for methionine) for transcriptionStop codons – UAA, UAG, UGAM.I/ASASI/2013 Page 24
  25. 25. 2. Redundant: – More than one codon for an amino acids 3. Unambigous – One codon can only specify an amino acid only – Which means if AAA is for Lysine, it is strictly for Lysine and cannot form other amino acid 4. No spaces or punctuationTranscription - Happens when the DNA strands separate - One strand of DNA is used as the pattern to produce RNA using specific base pairing - Catalyze by RNA polymerase - Takes place in nucleusFlow of transcriptionStart: promotercoding regionterminator:End • RNA synthesis – Is catalyzed by RNA polymerase, which pries the DNA strands apart and hooks together the RNA nucleotides – Follows the same base-pairing rules as DNA, except that in RNA, uracil(U) substitutes for thymine(T) • The stages of transcription are – Initiation – Elongation – TerminationM.I/ASASI/2013 Page 25
  26. 26. Initiation - RNA polymerase bind to promoter - DNA double helix unwind - RNA polymerase transcribe the coding region - No primer is needed for transcription because starts at the promoterWhat is promoter? - TATA box  TATA box is recognize by transcription factors  Transcription factors(TF) are proteins involve in the regulation of gene expression  TF has two domains(base)  At TATA box  For RNA polymerase to bindM.I/ASASI/2013 Page 26
  27. 27. - TF binds to DNA strand - RNA polymerase II bind to DNA at TF - TF + RNA polymerase + TATA box = transcription initiation complexElongationM.I/ASASI/2013 Page 27
  28. 28. - RNA polymerase elongate transcription from 5’ to 3’ - Transcribed DNA will reform the double helix - New RNA dissociate from templateTermination - RNA polymerase transcribes a terminator - Terminator is one of the three stop codons (UAA, UAG, UGA) - RNA strands released - RNA polymerase dissociates from the template strand • The mechanisms of termination – Are different in prokaryotes and eukaryotes • Eukaryotic cells modify RNA after transcription • Enzymes in the eukaryotic nucleus – Modify pre-mRNA in specific ways before the genetic messages are dispatched to the cytoplasm • Each end of a pre-mRNA molecule is modified in a particular way – The 5 end receives a modified nucleotide cap (capped with Guanine, G) – The 3 end gets a poly-A tail (Adenine, A)M.I/ASASI/2013 Page 28
  29. 29. Why mRNA ends need to be altered? - Protects the RNA from degradation - Helps the ribosome to attach to the mRNA - Facilitates the transport out of the RNA from the nucleusRNA splicing – Pre-mRNA contains Introns (non coding region) and Exons (coding region) – Removes introns and joins exons • RNA splicing Is carried out by spliceosomes in some cases • Ribozymes – Are catalytic RNA molecules that function as enzymes and can splice RNA • The presence of introns – Allows for alternative RNA splicingM.I/ASASI/2013 Page 29
  30. 30. Translation • A cell translates an mRNA message into protein – With the help of transfer RNA (tRNA) and ribosomes • Consist of three stages - Initiation, elongation and terminationTranslation: the basic concept • Molecules of tRNA are not all identical – Each carries a specific amino acid on one end – Each has an anticodon on the other end • Which means it has two attachment sites - Amino acids - AnticodonM.I/ASASI/2013 Page 30
  31. 31. • Ribosomes – Facilitate the specific coupling of tRNA anticodons with mRNA codons during protein synthesis • The ribosomal subunits – Are constructed of proteins and RNA molecules named ribosomal RNA or rRNA • The ribosome has three binding sites for tRNA at the large subunit – The P site – The A site – The E site  Small subunit is for mRNA binding siteE site – hold discharged amino acidP site – holds the tRNA growing polypeptide chainA site – holds the tRNA carrying the next amino acidM.I/ASASI/2013 Page 31
  32. 32. Initiation of TranslationElongation • In the elongation stage of translation – Amino acids are added one by one to the preceding amino acidM.I/ASASI/2013 Page 32
  33. 33. Termination • The final stage of translation is termination – When the ribosome reaches a stop codon in the mRNA • A number of ribosomes can translate a single mRNA molecule simultaneously - Forming a polyribosome Summary of transcription and translationM.I/ASASI/2013 Page 33

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