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CHAPTER 8

CHAPTER 8. Mendel and Heredity. I. The Origins of Genetics:. A. Terms Trait : A characteristic determined by a genes INHERITANCE - The passing of traits by heredity HEREDITY - The transmission of traits from parents to offspring. B. The History of Genetics. Gregor Mendel :

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CHAPTER 8

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  1. CHAPTER 8 Mendel and Heredity

  2. I. The Origins of Genetics: A. Terms • Trait: A characteristic determined by a genes • INHERITANCE- The passing of traits by heredity • HEREDITY- The transmission of traits from parents to offspring

  3. B. The History of Genetics Gregor Mendel: • An Austrian monk in the mid-1800’s • Studied math and science • “Father of Genetics”

  4. Mendel made observations within the monastery's garden. • Noticed that in pea plants, seven specific traits could be seen. • Mendel was interested in testing the predictability of the traits

  5. C. Mendel’s Breeding Experiments • Crossed pea plants with purple flowers with plants with white flowers • Mendel counted all offspring and analyzed the data

  6. The Genetic Work of Mendel

  7. Traits Expressed as Simple Ratios

  8. D. Monohybrid Crosses • Cross involving only one pair of contrasting traits. STEP 1: • Produce TRUE BREEDING strains • Ex: Purple plants only produce purple offspring • These plants make up the “P Generation” (parental)

  9. Step 2: • Cross-pollinate two P generation plants with contrasting traits • F1- First Filial Generation: • The offspring of the P generation • Record the number of F1 plants with each trait

  10. STEP 3: • F1plants self-pollinate • The offspring are called F2 Second Filial • Each plant was counted

  11. E. Mendel’s Results • F1 showed only one form of the trait • Missing trait reappeared in some of the F2 generation • 3:1 ratio in the F2 generation

  12. Mendel’s Work

  13. II. Mendel’s Theory A. Mendel’s 4 Hypotheses: 1. For each trait an individual has 2 copies of the gene (one from each parent) 2. There are alternative versions of genes called ALLELES

  14. Mendel’s Hypotheses Continued • Dominance and Recessiveness: • One factor isDominant, and hides, the other factorRecessive • Segregation: • Theeggandspermcarry only one of the possible alleles

  15. B. Mendel’s Findings in Modern Times • Dominant- First letter of the trait in capital (P- purple), • Recessive- First letter of the dominant trait in lower case (p- white)

  16. Homozygous vs. Heterozygous • Homozygous: 2 alleles are the same - Homozygous Dominant(PP) ”Pure” - Homozygous Recessive(pp) • Heterozygous: alleles are different (Pp) - Display the characteristics of the dominant trait • A genetic trait that appears in every generation of offspring is called dominant.

  17. Genotype vs. Phenotype Genotype: • The genetic makeup of an organism Phenotype: • External “physical” appearance of an organism(trait)

  18. C. The Laws of Heredity 1. Law of Segregation: • The 2 alleles for a trait segregate when gametes are formed 2. Law of Independent Assortment: • Dominant factorsdon’talways go with other dominant factors • Recessive factorsdon’talways go with other recessive factors

  19. III. Studying Heredity A. Punnet Squares • Diagram that predicts the outcome of a monohybrid cross • Four Boxes in a square

  20. Monohybrid Crosses

  21. Simulating a Dihybrid Cross

  22. Dihybrid Crosses: compares 2 contrasting traits at one time

  23. Test Crosses • Used to determine the genotype of an individual • A procedure in which an individual of unknown genotype is crossed with a homozygous recessive individual

  24. B. Probability: • Likelihood that a specific event will occur Probability = # of one kind of outcome total # of all possible outcomes

  25. C. Inheritance of Traits Pedigree : • History of how a trait has been inherited over several generations

  26. 1. Autosomal Traits • Autosomal will appear in both sexes equally • It affects a chromosome other than the 23rd pair

  27. 2. SEX-LINKED TRAITS -Traits with alleles found on the “X” chromosome -Males are more likely to express recessive sex-linked alleles because the single “X” has nothing to hide/mask the trait • Red/Green most common form of • color deficiency Ex: Colorblindness Hemophilia

  28. 3. SEX-INFLUENCED TRAITS -A trait that is expressed because of the presence of male or female sex hormones -Alleles that code for these are on the autosomes -Both males and females have same allele, but the trait is only expressed in one of the sexes Ex: Pattern Baldness B = dominant in males B’ = recessive in females

  29. IV. Complex Patterns of Inheritance A.) Polygenic Traits: -Trait that is controlled by two or more genes. Examples: • skin color • eye color • fingerprints

  30. B. Incomplete Dominance • Individual displays a phenotype intermediate “blending of genetic information” between the two parents Ex: Red Snapdragon + White Snapdragon = Pink Snapdragon Ex: Straight hair + Curly hair = Wavy hair

  31. C. Multiple Alleles • Genes with 3 or more alleles EX: Blood … A-B-O

  32. D. Codominance: • Two dominant alleles are expressed at the same time • Ex: IA + IB = AB blood type

  33. Genetic Disorders Mutation: A change in a gene due to damage or being copied incorrectly.

  34. A. SICKLE-CELL ANEMIA • Change in the shape of the RBC: • Results in anemia, clogs, pain, decreased blood flow, death…. • Primarily effects the black population • 1 in 500 births in USA A = Normal A’ = Sickle Cell

  35. B. HUNTINGTONS DISEASE • Dominant Disorder • 30-40’s, forgetfulness, loss of muscle control,mental illness, death • genetically programmed degeneration of brain cells *Can be detected by identifying short sections of DNA known as GENETIC MARKERS

  36. C. TAY-SACHS DISEASE • Recessive Disorder • fatty substance accumulate in the nerve cells of the brain • A child becomes blind, deaf, and unable to swallow. Muscles begin to atrophy and paralysis sets in • Children usually die by age 5

  37. D. CYSTIC FIBROSIS • Body produces an abnormally thick, sticky mucus • Faulty transport of salt within cells of organs such as the lungs and pancreas • very salty-tasting skin; • persistent coughing, • wheezing or pneumonia; • excessive appetite but poor weight gain

  38. D. CYSTIC FIBROSIS • 1 in 2500 people are born with it • More than 10 million people

  39. NONDISJUNCTIONS • Failure of chromatids to separate during Meiosis • Results in an egg or sperm with extra or missing chromosomes

  40. A. MONOSOMY Condition where the zygote has only 45 chromosomes Examples: • Turner Syndrome (XO) • CRI-DU-CHAT SYNDROME

  41. B. TRISOMY- • A condition where the zygote has 47 chromosomes • Examples: • Supermale (XYY) • Klinefelters Syndrome (XXY)

  42. -DOWN SYNDROME (trisomy) - Extra 21

  43. PATAU SYNDROME (trisomy 13)

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