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Genetics_Ottolini_Biology

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  • Male and female reproductive parts are enclosed in the same flower
  • Mendel’
  • Transcript

    • 1. Genetics
    • 2. Mendel & Simple Patterns of Inheritance
    • 3. Human Traits • Your physical traits resemble those of your parents. • Heredity = the passing of traits from parents to offspring
    • 4. Gregor Johann Mendel • Mendel was an Austrian monk who conducted breeding experiments with garden peas. • Developed rules which accurately predict patterns of heredity • Genetics = the branch of biology that focuses on heredity
    • 5. Useful Features in Peas 1. Many traits that have two clearly different forms (no intermediate forms) Mating can be easily controlled 2. – – 3. Self-fertilization Cross-fertilization Small, grows easily, matures quickly & produces many offspring
    • 6. Self-Pollination
    • 7. Cross-Pollination Cross= mate or breed two individuals
    • 8. Nature’s Pollinators • Insects (bees) • Vertebrates (birds & bats) • Wind • Water
    • 9. Mendel’s Observations: Traits are Expressed as Simple Ratios • First experiments involved monohybrid crosses • Monohybrid cross = a cross that involves one pair of contrasting traits
    • 10. Mendel’s Experiments: Step #1 • Self-pollinate each pea plant for several generations • True-breeding= all offspring display only one form of a particular trait • P generation = parental generation, the first two individuals crossed in a breeding experiment
    • 11. Mendel’s Experiment: Step #2 • Cross-pollinate the P generation plants with contrasting forms of a trait • F1 generation = the first filial generation, the offspring of the P generation • Characterize and count plants
    • 12. Mendel’s Experiment: Step #3 • Allow the F1 generation to self-pollinate • F2 generation = the second filial generation, the offspring of the F1 generation plants • Characterize and count plants
    • 13. Mendel’s Results • F1 generation showed only one form of the trait (e.g. purple flowers) – The other form of the trait disappeared (e.g. white flowers) – Reappeared in the F2 generation • 3:1 ratio of the plants in the F2 generation
    • 14. Expressing Ratios: Mendel’s F2 Generation 705 purple-flowered plants; 224 white-flowered plants • Reduce the ratio to its simplest form: 705/224 = 3.15 Purple 224/224= 1 White – Ratio can be written in a few different ways: • 3:1 • 3 to 1 • 3/1
    • 15. Are offspring simply a blend of their parents’ characteristics? • Before Mendel’s experiment: this was the theory (blending hypothesis) – Ex. Tall x Short = Medium Mendel’s Conclusion – Offspring have two genes for each trait (one gene from each gamete)
    • 16. Mendel’s Hypotheses: Hypothesis #1 • For each inherited trait, an individual has two copies of the gene – One gene from each parent
    • 17. Mendel’s Hypotheses: Hypothesis #2 • There are alternative versions of genes • Alleles = different versions of genes; an individual receives one allele from each parent
    • 18. Mendel’s Hypotheses: Hypothesis #3 • When two different alleles occur together, one may be completely expressed, while the other may have no observable effect on the organism’s appearance. • Dominant = the expressed form of a trait • Recessive = the trait which is not expressed when the dominant form of the trait is present
    • 19. Mendel’s Hypotheses: Hypothesis #4 • When gametes are formed, the alleles for each gene in an individual separate independently of one another. – Gametes = one allele for each inherited trait – Fertilization – each gamete contributes one allele
    • 20. Representing Alleles • Letters are often used to represent alleles • Dominant Alleles = capitalize the first letter of the trait – Purple flowers = P • Recessive Alleles = first letter of the dominant trait, in lowercase – White flowers = p
    • 21. Combinations of Alleles • Homozygous = if two alleles of a particular gene present in an individual are the same • Heterozygous = if two alleles of a particular gene present in an individual are different • Example: yellow peas (Y) are dominant to green peas (y) – Homozygous for yellow peas = YY – Heterozygous for yellow peas = Yy yy YY Yy
    • 22. Heterozygous Alleles - Ff • Only the dominant allele is expressed – Recessive allele is present but not expressed • Example: Freckles – Freckles, F = Dominant allele – No Freckles, f = Recessive allele – Individuals who are heterozygous for freckles (Ff) have freckles
    • 23. Genotype vs. Phenotype • Genotype = the set of alleles that an individual has – Uppercase letter is always written first • Phenotype = the physical appearance of a trait (determined by which alleles are present)
    • 24. Laws of Heredity: The Law of Segregation • Law of Segregation= the two alleles for a trait segregate (separate) when gametes are formed
    • 25. Laws of Heredity: The Law of Independent Assortment • Law of Independent Assortment = the alleles of different genes separate independently of one another during gamete formation – Example: alleles for plant height separate independently of the alleles for flower color http://www.sumanasinc.com/webconten – Applies to: • Genes on different chromosomes • Genes that are far apart on the same chromosome
    • 26. Punnett Squares & Probabilities
    • 27. Punnett Squares: Predicting Expected Results in Crosses • Punnett Square = a diagram that predicts the expected outcome of a genetic cross by considering all possible combinations of gametes in the cross
    • 28. Punnett Squares • Possible gametes from one parent are written along the top of the square • Possible gametes from the other parent are written along the left side of the square • Letters inside the boxes = possible genotypes of the offspring
    • 29. Monohybrid Crosses • Homozygous for yellow seeds (YY) x Homozygous for green seeds (yy) = – Only yellow heterozygous offspring (Yy)
    • 30. Monohybrid Crosses • Heterozygous for yellow seeds (Yy) x heterozygous for yellow seeds (Yy) = – ¼ YY (Homozygous dominant) – 2/4 Yy (Heterozygous) – ¼ yy (Homozygous recessive) • 1 YY: 2 Yy: 1 yy genotypic ratio
    • 31. Let’s Solve a Punnett Square!!! •Inflated pod shape is DOMINANT • Constricted pod shape is RECESSIVE
    • 32. Step #1: Choose a Letter to Represent your Alleles • Inflated pea pod = I (dominant) • Constricted pea pod = i (recessive)
    • 33. Step #2: Write the Genotypes of the Parents • Parent #1 = Ii = Heterozygous Inflated • Parent #2 = Ii = Heterozygous Inflated
    • 34. Step #3: Determine the Possible Gametes • Parent #1 = Ii = I or i • Parent #2 = Ii = I or i
    • 35. Step #4: Enter the possible gametes at the top and side of the Punnett Square I I i i
    • 36. Step #5: Write the alleles from the gametes in the appropriate boxes I i I II Ii i Ii ii
    • 37. Step #6: Determine the phenotypes of the offspring I i Inflated Pods Inflated Pods I II Ii Inflated Pods i Ii ii Constricted Pods
    • 38. Step #7: Determine the genotype and phenotype ratios I i Inflated Pods Inflated Pods I II Ii Inflated Pods i Ii ii Constricted Pods Genotype Ratio: 1 II : 2 Ii : 1 ii Phenotype Ratio: 3 Inflated : 1 Constricted
    • 39. Probabilities Can Also Predict the Expected Results of Crosses • Probability = the likelihood that a specific event will occur – Words – 1 out of 1 – Decimal – 1 – Percentage – 100% – Fraction – 1/1 Probability = number of one kind of possible outcome ÷ total number of all possible outcomes
    • 40. Probability in Pea Plants: Gamete • Parent = Yy – Can either contribute a yellow allele (Y) or a green allele (y) • ½ chance that the gamete will have Y • ½ chance that the gamete will have y
    • 41. Probability of the Outcome of a Cross • Consider the offspring of two parents who are heterozygous for freckles: – Mom = Ff • Possible gametes from mom = F • ½ probability of mom contributing F • ½ probability of mom contributing f or f or f – Dad = Ff • Possible gametes from dad = F • ½ probability of dad contributing F • ½ probability of dad contributing f
    • 42. Probability of the Outcome of a Cross – Mom F + Dad F = FF (1/2) x (1/2) = ¼ probability of FF (freckles) – Mom F + Dad f = Ff (1/2) x (1/2) = ¼ probability of Ff (freckles) – Mom f + Dad F = Ff (1/2) x (1/2) = ¼ probability of Ff (freckles) – Mom f + Dad f = ff (1/2) x (1/2) = ¼ probability of ff (no freckles)
    • 43. Probability of the Outcome of a Cross • Genotype Probabilities: – ¼ FF (freckles) – ¼ Ff + ¼ Ff = ½ Ff (freckles) – ¼ ff (no freckles) • Phenotype Probabilities: – ¼ FF + ½ Ff = ¾ freckles – ¼ ff = ¼ no freckles
    • 44. Pedigrees
    • 45. Studying Pedigrees: How are traits inherited??? • Pedigree= a family history that shows how a trait is inherited over several generations
    • 46. Why are pedigrees helpful/useful? Common Genetic Disorders: • Pedigrees are helpful if couples are concerned that they might be carriers of genetic disorders Angelman Syndrome Canavan Disease Charcot-Marie-Tooth Disease Cri du Chat Syndrome Duchenne Muscular Dystrophy Fragile X Syndrome Gilbert's Syndrome Joubert Syndrome Klinefelter Syndrome Krabbe Disease Lesch–Nyhan Syndrome Myotonic Dystrophy Neurofibromatosis Noonan Syndrome Pelizaeus-Merzbacher Disease Phenylketonuria Porphyria Prader-Willi Syndrome Retinoblastoma Rubinstein-Taybi Syndrome
    • 47. Pedigree Symbols
    • 48. Pedigree Numbers • Roman numerals (I, II, III, IV) represent = Generations •Regular numbers (1,2,3,4) represent = Individuals in each generation
    • 49. Pedigree Symbols – Male and Female = Normal Male = Normal Female Horizontal line between a male and female indicates MATING/MARRIAGE = Male with trait = Female with trait Branching vertical lines point to OFFSPRING
    • 50. Autosomal vs. Sex-linked Traits • Autosomal Trait = appears in both sexes equally, alleles appear on the autosomal chromosomes • Sex-linked Trait = a trait whose allele is located on the X chromosome – Appears mostly in males – Mostly recessive – Female only exhibits the condition if she inherits two recessive alleles
    • 51. Human Chromosomes • Humans have 46 chromosomes: – 1 pair of sex chromosomes (X and Y) – 22 pairs of autosomes • Females have 2 X chromsomes (XX). • Males have an X chromsome and a Y chromosome (XY)
    • 52. Karyotypes • A Karyotype is a test to identify and evaluate the size, shape, and number of chromosomes in a sample of body cells.
    • 53. Dominant vs. Recessive Trait • Autosomal Dominant Traits = each individual with the trait will have a parent with the trait • Autosomal Recessive Traits = an individual with the trait can have one, two, or neither parent who exhibit the trait
    • 54. Recessive Disorder: Albinism • Albinism = a genetic disorder in which the body is unable to produce an enzyme necessary for the production of melanin (dark color to hair, skin, scales, eyes, and feathers)
    • 55. Genetic Disorders = Carriers • Carriers = individuals who are heterozygous for a recessive inherited disorder, but do not show symptoms of the disorder – Can pass the recessive allele for the disorder to their offspring
    • 56. Red-Green Color Blindness: A Sex-Linked Recessive Disorder • X-linked recessive disorder • Among Caucasian individuals: – 8% of males – 0.5% of females • Difficulty distinguishing between shades of green and red
    • 57. Red-Green Color Blindness: A Sex-Linked Recessive Disorder Males have the disorder more often than females because they only have one X chromosome. • Unaffected female = • Affected female = • Carrier female = • Unaffected male = XRY • Affected male = XrY XRXR XrXr XRXr
    • 58. Red-Green Color Blindness: A Sex-Linked Disorder
    • 59. Heterozygous vs. Homozygous • Homozygous Dominant or Heterozygous individuals = phenotype will show the dominant characteristic • Homozygous Recessive individuals = phenotype will show the recessive characteristic ***Heterozygous carriers of a recessive mutation will not show the mutation, can produce children who are homozygous for the recessive allele
    • 60. Let’s look at a pedigree for polydactyly: a dominant trait
    • 61. Let’s look at a pedigree for phenylketonuria (PKU): a recessive disorder The trait skips a generation!!
    • 62. Complex Patterns of Inheritance
    • 63. Traits Influenced by Several Genes • Polygenic Trait = when several genes influence a trait – Genes can be: • Scattered along the same chromosome • Located on different chromosomes – Independent Assortment = many different combinations in offspring • Polygenic traits = – Eye color, height, weight, hair and skin color
    • 64. Polygenic Trait – Skin Color
    • 65. Intermediate Traits • Incomplete Dominance = an individual displays a trait that is intermediate between the two parents • Examples: – Red snapdragon + White snapdragon = Pink snapdragon offspring – Curly hair + Straight hair = Wavy haired offspring • Neither allele is dominant to the other
    • 66. Pink Snapdragon - Heterozygous
    • 67. Traits With Two Forms Displayed At The Same Time • Codominance = when two dominant alleles are expressed at the same time, both forms of the trait are displayed • Example: – Red Horse + White Horse = Roan Horse
    • 68. Roan Horse - Heterozygous
    • 69. Traits Controlled By Genes With Three or More Alleles • Multiple Alleles = Genes with three or more alleles • Example: ABO blood groups in humans – IA and IB = Dominant to i; • A & B are two carbohydrates on the surface of red blood cells – i = Recessive – When IA and IB are present together = Codominant
    • 70. Traits Controlled By Genes With Three or More Alleles • An individual can only have two of the possible alleles for the gene
    • 71. Genotypes of Each Blood Type
    • 72. Traits Influenced By The Environment • Phenotype is affected by environmental conditions • Hydrangeas (flowers) range from blue to pink based upon the pH of the soil – Acidic soil = blue flowers – Basic soil = pink flowers
    • 73. Traits Influenced By The Environment • Siamese Cat – Fur on ears, nose, paws, and tail is darker than the rest of the body – Dark fur at locations which are cooler than normal body temperature
    • 74. Traits Influenced by the Environment: Identical Twins
    • 75. Human Examples: Traits Influenced By The Environment • Height – What can influence height besides genes? • Skin Color • Human Personality
    • 76. Traits Caused By Mutation • Damaged genes/genes which are copied incorrectly – result in faulty proteins • Mutations are RARE • Inherited Mutations cause Genetic Disorders • Many mutations are carried in recessive alleles – Carrier = heterozygous individual • Carry the recessive allele but do not exhibit the disorder
    • 77. Sickle Cell Anemia • Recessive • Defective hemoglobin – Red Blood Cells – Binds and transports oxygen • Sickle-Cell Shape – Rupture-prone – Clotting in blood vessels • Heterozygote Advantage = protection from malaria
    • 78. Hemophilia • Recessive • Sex-linked – X chromosome – More males afflicted than females • Impairs blood clotting • English royal family
    • 79. Hemophilia: The Royal Family
    • 80. Huntington’s Disease • Dominant • First symptoms appear in thirties or forties: – Mild forgetfulness – Irritability • Long-term symptoms: – Loss of muscle control – Chorea (physical spasms) – Severe Mental Illness – Death
    • 81. Detecting and Treating Genetic Disorders • Genetic Counseling = a form of medical guidance that informs people about genetic problems that could affect them or their offspring • Phenylketonuria (PKU) – Lacks enzyme to convert phenylalanine into tyrosine – Can cause mental retardation – Early intervention involves low-phenylalanine diet • Gene Therapy = replacing defective genes with healthy ones

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