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  1. 1. Patterns of Inheritance
  2. 2.  One of the most exciting fields of biology is the study of patterns of inheritance or GENETICS
  3. 3. What is genetics? • It is the study of the mechanism of heredity and variations by which traits or characteristics are passed from one generation to another • These mechanisms are dependent on the behavior of chromosomes during the formation of sex cells (meiosis) and the way in which this • cells are brought together in fertilization
  4. 4. What is heredity? Refers to the similarities between parents and offspring It is the transfer of genetically controlled characteristics from one generation to the next Examples: hair color and color of the eyes, height, intelligence(human) flower color (plants)
  5. 5. What is variation? Variation is difference, whether in the expression of somatic characters or in the elements of the germinal substance, exhibited among groups of organisms related by descent (ancestors).
  6. 6. Example of variation: At the time the chromosome theory of inheritance was proposed, scientists began studying the inheritance of traits in the fruit fly (Drosophila melanogaster) In a bottle containing normal (wild type) red-eyed flies, a white- eyed fly was discovered in a bottle. This variation was produced by mutation- an inherited change in the gene controlling the eye color
  7. 7. Chromosomal mutation affect the number and structure of chromosomes. Mutation whether genetic or chromosomal are defined as any heritable change and are the sources of all genetic variation Mutation therefore is a random change in a gene or chromosome resulting in a new trait or characteristic that can be inherited.  Mutation can be a source of beneficial genetic variation, or it can be neutral or harmful in effect.
  8. 8. History ofHistory of GeneticsGenetics
  9. 9. 9 Gregor MendelGregor Mendel (1822-1884)(1822-1884) ResponsibleResponsible for the Lawsfor the Laws governinggoverning Inheritance ofInheritance of TraitsTraits
  10. 10. 10 Gregor Johann MendelGregor Johann Mendel Austrian monkAustrian monk Studied theStudied the inheritanceinheritance of traitsof traits inin pea plantspea plants Developed theDeveloped the laws of inheritancelaws of inheritance Mendel's work wasMendel's work was not recognized untilnot recognized until the turn of thethe turn of the 20th20th centurycentury
  11. 11. 11 Gregor Johann MendelGregor Johann Mendel BetweenBetween 1856 and1856 and 1863,1863, MendelMendel cultivated andcultivated and tested sometested some 28,00028,000 pea plantspea plants He found that theHe found that the plants' offspringplants' offspring retainedretained traits of thetraits of the parentsparents Called theCalled the “Father“Father of Genetics"of Genetics"
  12. 12. 12 He bred gardenHe bred garden peas in thepeas in the monastery gardenmonastery garden and analyzed theand analyzed the offspring of theseoffspring of these crossescrosses Site of GregorSite of Gregor Mendel’sMendel’s experimentalexperimental garden in thegarden in the Czech RepublicCzech Republic
  13. 13. 13 Reasons why Mendel choseReasons why Mendel chose garden peas (garden peas (Pisum sativum)Pisum sativum) 1.1. Can be grown in aCan be grown in a small areasmall area .2 Plants Reproduce.2 Plants Reproduce at a fast rateat a fast rate . ,3 Thus a number. ,3 Thus a number ofof generations cangenerations can bebe produced withinproduced within
  14. 14. 14 Reasons why Mendel choseReasons why Mendel chose garden peas (garden peas (Pisum sativum)Pisum sativum) .4.4 They are hardyThey are hardy plants which doplants which do not need muchnot need much caring andcaring and cultivatingcultivating .5 Plants Produce.5 Plants Produce lots of offspringlots of offspring
  15. 15. 15 Reasons why Mendel choseReasons why Mendel chose garden peas (garden peas (Pisum sativum)Pisum sativum) 66. Produce pure plants. Produce pure plants when allowed towhen allowed to -self-self pollinate severalpollinate several generationsgenerations .7 Can be artificially.7 Can be artificially -cross pollinated-cross pollinated .8 Garden pea has.8 Garden pea has several contrastingseveral contrasting characterscharacters
  16. 16. 16 Reproduction in Flowering PlantsReproduction in Flowering Plants Pollen contains spermPollen contains sperm Produced by theProduced by the stamenstamen Ovary contains eggsOvary contains eggs Found inside theFound inside the flowerflower Pollen carries sperm to thePollen carries sperm to the eggs for fertilizationeggs for fertilization Self-fertilizationSelf-fertilization cancan occur in the same floweroccur in the same flower Cross-fertilizationCross-fertilization cancan occur between flowersoccur between flowers
  17. 17. 17 Eight Pea Plant TraitsEight Pea Plant Traits Seed shapeSeed shape ------ Round (R) or Wrinkled (r)Round (R) or Wrinkled (r) Seed ColorSeed Color -------- Yellow (Y) or Green (Yellow (Y) or Green (yy)) Pod ShapePod Shape ------ Smooth (S) or wrinkled (Smooth (S) or wrinkled (ss)) Pod ColorPod Color ------ Green (G) or Yellow (g)Green (G) or Yellow (g) Seed Coat ColorSeed Coat Color ------Gray (G) or White (g)Gray (G) or White (g) Flower positionFlower position------Axial (A) or Terminal (a)Axial (A) or Terminal (a) Plant HeightPlant Height ------ Tall (T) or Short (t)Tall (T) or Short (t) Flower color ---Flower color --- Purple (P) or white (Purple (P) or white (pp)) TRAITS CORRESPONDING CHARACTERS
  18. 18. Mendel’s Peas
  19. 19. 19 How Mendel Began his expt.How Mendel Began his expt. Mendel produced pure strains by allowing the plantsMendel produced pure strains by allowing the plants to self-pollinate for several generationsto self-pollinate for several generations This way he was sure that the character (ex. round seeds) was “pure”. All the pea plants which he cultivated for this purpose produced only “round seeds”
  20. 20. 20 How Mendel Began his expt.How Mendel Began his expt. •He describe such plants which produce the same character from generation to generation as pure- breeding or “breed true”. Mendel did the same with the plants bearing wrinkled seeds
  21. 21. Second step: he cross pollinate the pure breed of round seeded plants with the wrinkled seeded plants Round seed x Wrinkled seedRound seed x Wrinkled seed F1: All round seedF1: All round seed
  22. 22. TRAIT P1 GENERATION (Cross Pollinated) F1 GENERATION Shape of Seed Round X Wrinkled All round Color of Seed Yellow X Green All yellow Color of Seed Coats Colored X White All colored Shape of Pod Inflated X Constricted All inflated Color of Pod Green X Yellow All green Position of Flowers Axial X Terminal All axial Length of Stem Long X Short All long Color of the Flowers Purple X White All purple FIND OUT FROM THE TABLE BELOW WHICH OF THE CHARACTERS ARE DOMINANT AND WHICH ARE RECESSIVE Mendel’s P1 Crosses (Cross-Pollination)
  23. 23. 23
  24. 24. 24
  25. 25. MENDELLIAN LAWS OF GENETICS From the results of his experiments, he formulated the three laws: 1.Law of Dominance 2.Law Segregation 3.Law of Independent Assortment
  26. 26. Law of Complete DominanceLaw of Complete Dominance States that a cross between homozygous dominant genes and homozygous recessive genes will result in a progeny of heterozygous genes determining all dominant traits (all the offspring will show only one of the characters) The trait that is observed in the offspring is the dominant trait The trait that disappears in the offspring is the recessive trait
  27. 27. Parental Phenotypes:Parental Phenotypes: Curly Hair x Straight HairCurly Hair x Straight Hair Genotypes:Genotypes: CCCC cccc Curly HairsCurly Hairs CcCc EXAMPLE: FOUND IN YOUR BOOK Phenotype of offspring: Genotype of offspring: 100% curly 100% Cc
  28. 28. Third Step Of His ExperimentThird Step Of His Experiment F2: 5474 round: 1850 wrinkledF2: 5474 round: 1850 wrinkled (3/4 round to 1/4 wrinkled)(3/4 round to 1/4 wrinkled) Round seed x Wrinkled seedRound seed x Wrinkled seed F1: All round seedF1: All round seed F1 round plantsF1 round plants xx F1 round plantsF1 round plants He allowed the F1 plants to self pollinate
  29. 29. Law of DominanceLaw of Dominance 29
  30. 30. Generation “Gap”Generation “Gap” Parental PParental P11 GenerationGeneration == the parentalthe parental generation in a breeding experimentgeneration in a breeding experiment.. FF11 generationgeneration == the first-generationthe first-generation offspring in a breeding experiment.offspring in a breeding experiment. (1st filial generation)(1st filial generation) From breeding individuals from the PFrom breeding individuals from the P11 generationgeneration FF22 generationgeneration == the second-generationthe second-generation offspring in a breeding experiment.offspring in a breeding experiment. (2nd filial generation)(2nd filial generation) From breeding individuals from theFrom breeding individuals from the30
  31. 31. Following the GenerationsFollowing the Generations 31 Cross 2Cross 2 PurePure PlantsPlants TT x ttTT x tt Results inResults in allall HybridsHybrids TtTt Cross 2 HybridsCross 2 Hybrids getget 3 Tall & 1 Short3 Tall & 1 Short TT, Tt, ttTT, Tt, tt
  32. 32. TRAIT P1 GENERATION (Cross Pollinated F1 GENERATION Actual Ratio Shape of Seed Round X Round 5, 474 round 1,850 wrinkled 7,324 total 2.93:1 Color of Seed Yellow X Yellow 6,022 yellow 2001 white 8023 total 3.01:1 Color of Seed Coats Colored X Colored 705 colored 224 white 929 total 3.15:1 Shape of Pod Inflated X Inflated 882 imnflated 229 constricted 1181 total 2.95:1 Color of Pod Green X Green 428 green 152 yellow 580 total 2.82:1 Position of Flowers Axial X Axial 651 axial 207 terminal 858 total 3.4:1 Length of Stem Long X Long 787 long 288 short 1064 total 2.84:1 Mendel’s P2 Crosses (Self pollination)
  33. 33. Mendel analyzed the data closely. To his surprise there was a pattern in the results. He also noticed that the greater number of offspring produced, the clearer was the pattern It shows in the 4th column that in the F2 generation, the ratio of the plants with the dominant character to the plants with the recessive character was almost 3:1
  34. 34. From the results of his P2 crosses, he formulated his second law –The law of Segregation- states that individuals carry two hereditary alleles affecting any given character According to this law also that, the determiner of a recessive character, which does not appear in the F1 (Rr) generation, separates from the chance for the determiners of the recessive character to combine during reproduction, and appear in the F2 Law of SegregationLaw of Segregation
  35. 35. Mendel reasoned that each of the F1 plants must have contained two determiners, one for round seed and one for wrinkled seed. However , the determiner for round seed masked the determiner fro wrinkled seed . Mendel used the term “unit determiner” for what we called as “GENES” now
  36. 36. The same gene can have many versions • A gene is a piece of DNA that directs a cell to make a certain protein. • Each gene has a locus, a specific position on a pair of homologous chromosomes.
  37. 37. • An allele is any alternative form of a gene occurring at a specific locus on a chromosome. – Each parent donates one allele for every gene. – Homozygous describes two alleles that are the same at a specific locus. – Heterozygous describes two alleles that are different at a specific locus. – The 2 alleles are known to be found on copies of chromosomes – one from each parent–
  38. 38. Alleles can be represented using letters – A dominant allele is expressed as a phenotype when at least one allele is dominant. – A recessive allele is expressed as a phenotype only when two copies are present. – Dominant alleles are represented by uppercase letters; recessive alleles by lowercase letters.
  39. 39. To make easier for him to analyze the results of his experiments, he designated symbols for the characters PLANT (GARDEN PEA) SYMBOLS Pure breeding P1 plant bearing round seeds RR Pure breeding P1 plant bearing wrinkled seeds rr F1 Plants bearing round seeds Rr
  40. 40. Mendel said that during formation of gametes, the determiners separate. Hence only one member of a pair of determiners goes to a gamete HomozygousHomozygous DominantDominant HomozygousHomozygous RecessiveRecessive HeterozygousHeterozygous Round seed x Wrinkled seedRound seed x Wrinkled seed RR rrRR rr F1: All round seed coatsF1: All round seed coats RrRr
  41. 41. R R R R Homozygous parents can only pass oneHomozygous parents can only pass one form of an allele to their offspring.form of an allele to their offspring.
  42. 42. R r R r Heterozygous parents can pass eitherHeterozygous parents can pass either of two forms of an allele to their offspring.of two forms of an allele to their offspring.
  43. 43. TERMINOLOGIES • PHENOTYPE – the way an organism looks and behaves- its physical characteristics (Ex. Tall, short, green, white, brown hair, blue eyes, etc. ) • GENOTYPE – the gene combination (allelic combination) of an organism – Ex. TT, Tt, tt, etc.) PhenotypePhenotype:: Round seedRound seed Genotype :Genotype : RR (homozygous dominant)RR (homozygous dominant) Rr (heterozygous dominantRr (heterozygous dominant)) Phenotype:Phenotype: Wrinkled seedWrinkled seed Genotype:Genotype: rr (homozygous recessive)rr (homozygous recessive) Principles of Heredity
  44. 44. – HOMOZYGOUS – 2 ALLELES ARE THE SAME when an organism possesses two identical alleles. ex. YY or yy – HETEROZYGOUS – 2 ALLELES DIFFERENT when an organism possesses different alleles. ex. Yy
  45. 45. Law of Segregation In the formation of gametes, the members of a pair of alleles separate (or segregate) cleanly from each other so that only one member is included in each gamete. Each gamete has an equal probability of containing either member of the allele pair. When gametes (sperm, egg) areWhen gametes (sperm, egg) are formed, each gamete will receiveformed, each gamete will receive one allele or the allele or the other.
  46. 46. Law of Segregation • 1. A pea plant contains two discrete hereditary factors, one from each parent • 2. The two factors may be identical or different • 3. When the two factors of a single trait are • different – One is dominant and its effect can be seen – The other is recessive and is masked • 4. During gametogenesis (meiosis), the paired factors segregate randomly so that half of the gametes received one factor and half of the gametes received the other – This is Mendel’s Law of Segregation 2-25
  47. 47. Monohybrid cross (cross with only 1 trait) • Problem: • Using this is a several step process, look at the following example – Tallness (T) is dominant over shortness (t) in pea plants. A Homozygous tall plant (TT) is crossed with a short plant (tt). What is the genotypic makeup of the offspring? The phenotypic makeup ?
  48. 48. Punnett Squares • Genetic problems can be easily solved using a tool called a Punnett Square. – Tool for calculating genetic probabilities A punnett squareA punnett square
  49. 49. Punnet Square Process 1. Determine alleles of each parent, these are given as TT, and tt respectively. 2. Take each possible allele of each parent, separate them, and place each allele either along the top, or along the side of the punnett square.
  50. 50. Punnett process continued • Lastly, write the letter for each allele across each column or down each row. The resultant mix is the genotype for the offspring. In this case, each offspring has a Tt (heterozygous tall) genotype, and simply a "Tall" phenotype.
  51. 51. Punnett process continued • Here we have some more interesting results: First we now have 3 genotypes (TT, Tt, & tt) in a 1:2:1 genotypic ratio. We now have 2 different phenotypes (Tall & short) in a 3:1 Phenotypic ratio. This is the common outcome from such crosses.
  52. 52. F1 GENERATIONF1 GENERATION FATHERFATHER MOTHERMOTHER T tT t T tT t TT TT TT tt tt tt F2 GENERATIONF2 GENERATION - the- the law of dominancelaw of dominance explained the heredity ofexplained the heredity of the offspring ofthe offspring of the f1 generationthe f1 generation - the- the law of segregationlaw of segregation explained the heredity ofexplained the heredity of thethe f2 generationf2 generation
  53. 53. Another Example of Monohybrid Cross Smooth and wrinkled parental seed strains crossed. F1 genotypes F1 phenotypes 4/4 Ss 4/4 smooth
  54. 54. With the previous example , apply the law of segregation and find the phenotypic ratio and genotypic ratio of the F2. Seat work:
  55. 55. ANSWER Parentals:Parentals: SS x ssSS x ss S S s sS S s s SS SS s ss s F1 x F1:F1 x F1: Ss x SsSs x Ss R r R rR r R r ½ S½ S ½ s½ s ½ S ½ s½ S ½ s ¼ SS¼ SS ¼ Ss¼ Ss ¼ Ss¼ Ss ¼ ss¼ ss SsSs SsSs SsSs SsSs Genotypic RatioGenotypic Ratio: ¼ RR + ½ Rr + ¼ rr or 1:2:1: ¼ RR + ½ Rr + ¼ rr or 1:2:1 Phenotypic RatioPhenotypic Ratio: ¾ Round + ¼ Wrinkled: ¾ Round + ¼ Wrinkled
  56. 56. Law of Independent Assortment -states that alleles of different genes are distributed randomly to the gametes and fertilization occurs at random - To explain this law, a dihybrid cross will be used. This type of cross uses two traits.
  57. 57. Dihybrid crosses • Dihybrid crosses are made when phenotypes and genotypes composed of 2 independent alleles are analyzed. • Process is very similar to monohybrid crosses. • Example: – 2 traits are being analyzed – Plant height (Tt) with tall being dominant to short, – Flower color (Ww) with Purple flowers being dominant to white.
  58. 58. Dihybrid cross example • The cross with a pure-breeding (homozygous) Tall, Purple plant with a pure-breeding Short, white plant should look like this. F1 generationF1 generation
  59. 59. Dihybrid cross example continued • Take the offspring and cross them since they are donating alleles for 2 traits, each parent in the F1 generation can give 4 possible combination of alleles. TW, Tw, tW, or tw. The cross should look like this. (The mathematical “foil” method can often be used here) F2 GenerationF2 Generation F1 generationF1 generation
  60. 60. Dihybrid cross example continued • Note that there is a 9:3:3:1 phenotypic ratio. 9/16 showing both dominant traits, 3/16 & 3/16 showing one of the recessive traits, and 1/16 showing both recessive traits. • Also note that this also indicates that these alleles are separating independently of each other. This is evidence of Mendel's Law of independent assortment
  61. 61. Mendel’s Principle of Independent Assortment When gametes are formed, the alleles of one gene segregate independently of the alleles of another gene producing equal proportions of all possible gamete types.
  62. 62. Genetic Segregation + Independent Assortment Parentals:Parentals: RRYY x rryyRRYY x rryy RY RY RY RY ry ry ry ryRY RY RY RY ry ry ry ry ryry RYRY RrYyRrYy F1: 100% RrYy, round, yellowF1: 100% RrYy, round, yellow
  63. 63. F1 x F1: RrYy x RrYy RY Ry rY ry RY Ry rY ry ¼ RY ¼ Ry ¼ rY ¼ ry ¼ RY ¼ Ry ¼ rY ¼ ry 1/16 RRYY 1/16 RRYy 1/16 RrYY 1/16 RrYy 1/16 RRYy 1/16 RRyy 1/16 RrYy 1/16 Rryy 1/16 RrYY 1/16 RrYy 1/16 rrYY 1/16 rrYy 1/16 RrYy 1/16 Rryy 1/16 rrYy 1/16 rryy 1 432 9 8765 16151413 10 11 13
  64. 64. F2 Genotypes and PhenotypesF2 Genotypes and Phenotypes PhenotypesPhenotypes GenotypesGenotypes RoundRound YellowYellow 1/16 RRYY + 2/16 RRYy +1/16 RRYY + 2/16 RRYy + 2/16 RrYY + 4/16 RrYy2/16 RrYY + 4/16 RrYy Total = 9/16 R_Y_Total = 9/16 R_Y_ RoundRound GreenGreen 1/16 RRyy+ 2/16 Rryy1/16 RRyy+ 2/16 Rryy Total = 3/16 R_yyTotal = 3/16 R_yy Wrinkled YellowWrinkled Yellow 1/16 rrYY+ 2/16 rrYy1/16 rrYY+ 2/16 rrYy Total = 3/16 rrY_Total = 3/16 rrY_ Wrinkled GreenWrinkled Green 1/16 rryy1/16 rryy
  65. 65. Refer to figure above: Start with the shape of the seed List down your answers on a piece of paper Note: Mendel explained these observations as follows: -The determiners for seed shape are inherited separately from the determiners for seed colors -That is Mendel’s Law of Independent Assortment of determiners. The inheritance of seed coats has no effect on the inheritance of seed color, each character is inherited as a unit. Suppose you describe the appearance of the offspring in the table above , what are their phenotypes? What are their Genotypes?
  66. 66. Meiotic Segregation explainsMeiotic Segregation explains Independent AssortmentIndependent Assortment
  67. 67. THE NON-MENDELIAN LAWS OF INHERITANCE •Refer to hereditary patterns that are not in accordance with Mendel’s principles or those that are not attributed to single autosomal genes.
  68. 68. A. Law of Incomplete Dominance - this principle states that a cross between homozygous dominant and recessive genes will result in a progeny of heterozygous dominant and recessive trait. Both alleles exert an effect and jointly produce an intermediate phenotype.
  69. 69. See book: A cross using colors of the petals of flower (red and white) Parentals:Parentals: RR x rrRR x rr R R r rR R r r RR RR r rr r RrRr RrRr RrRr RrRr Genotype of offspringGenotype of offspring: 100% Rr: 100% Rr Phenotype of offspringPhenotype of offspring: 100% pink: 100% pink Genotypic offspring: Rr; Rr; Rr; Rr Phenotype of offspring: pink; pink; pink; pink The resulting genotypes of the offspring are all heterozygous (Rr) just like in the first law, however the phenotype that is expressed is not the dominant trait red, rather, an intermediate color between red and white which is PINK
  70. 70. B.LAW OF CO-DOMINANCE o This principle states that a cross between homozygous dominant genes will result in a progeny of heterozygous genes determining a phenotype where a mix of the dominant recessive traits is expressed.
  71. 71. Look at the diagram in your book to show this kind of cross. This time the trait used is the color of coat of cattle Parentals:Parentals: CR = red color coatred color coat;; Cr = white color coatwhite color coat CR CR xx Cr Cr CR CR Cr Cr CR CR Cr Cr CR Cr Genotype of offspringGenotype of offspring: 100%: 100% CR Cr Phenotype of offspringPhenotype of offspring: 100% roan: 100% roan Genotype of offspring: CR Cr - CR Cr – CR Cr- CR Cr Phenotype of offspring: roan; roan; roan; roan CR Cr CR Cr CR Cr
  72. 72. The roan phenotype appears pink in color, but with respect to the hair composition, some are red and some are white. The blending of red and white hair will appear pink. The difference of this cross is that the dominant trait (red hair) is expressed equally with the recessive trait (white hair). There is the absence of the intermediate trait that was present in then previous cross of incomplete dominance
  74. 74. THANK YOU