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Concept 10.1

Concept 10.1. GENETICS DEVELOPED FROM CURIOSITY ABOUT INHERITANCE. Austrian monk who developed two laws of heredity in 1860‘s Mendel’s work gave rise to the field of genetics —the study of heredity Mendel’s work was unrecognized until 1900. GREGOR MENDEL: FATHER OF MODERN GENETICS.

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Concept 10.1

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  1. Concept 10.1 GENETICS DEVELOPED FROM CURIOSITY ABOUT INHERITANCE

  2. Austrian monk who developed two laws of heredity in 1860‘s Mendel’s work gave rise to the field of genetics—the study of heredity Mendel’s work was unrecognized until 1900 GREGOR MENDEL: FATHER OF MODERN GENETICS

  3. BEFORE MENDEL: BLENDING HYPOTHESIS OF INHERITANCE • Blending Hypothesis: offspring will possess traits intermediate between those of different parents • EXAMPLE: crossing red and yellow flowers will produce orange flowers

  4. BEFORE MENDEL: BLENDING HYPOTHESIS OF INHERITANCE • Exceptions to blending hypothesis were observed • Offspring of parents with red flowers sometimes had yellow flowers • Hypothesis was later discarded • Did not explain how traits that disappear in one generation sometimes reappear in later ones

  5. GREGOR MENDEL: THE PARTICULATE HYPOTHESIS • Mendel proposed that traits in organisms result from “factors” that are passed on to offspring by each parent.  • Stated that the “factors” that control traits do not disappear between generations • Stressed this point even though the trait controlled by these “factors” may not be seen in the offspring of every generation

  6. GREGOR MENDEL: THE PARTICULATE HYPOTHESIS • Particulate hypothesis: parents pass on separate and distinct “factors” that are responsible for inherited traits in their offspring • Hypothesis was proven to be correct • Provided a clear mechanism for the inheritance of traits • Today, Mendel’s “factors” are known to be genes

  7. TERMINOLOGY • Trait: an inherited characteristic; a variation of a particular character • Heredity: passing of traits from parents to offspring • Genetics: the study of heredity

  8. TERMINOLOGY • Self fertilization: occurs in flowers of plants with both male and female parts of plant within same flower—pollen fertilizes eggs within same plant • Cross-fertilization:pollen from flower of one plant fertilizes the eggs in flower different plant

  9. Self-fertilization occurs in same plant Cross-fertilization occurs in different plants TYPES OF FERTILIZATION

  10. Concept 10.2 MENDEL DISCOVERED THAT INHERITANCE FOLLOWS RULES OF CHANCE

  11. TERMINOLOGY • P generation: original parents in a genetic cross • F1 generation: offspring of the “P” generation • F2 generation: offspring of the “F1” generation that self-fertilize

  12. TERMINOLOGY • Alleles: alternative forms of a gene for a trait  designated by letters • EXAMPLE: gene for flower color in peas has two forms—one for purple flowers and one for white flowers

  13. TERMINOLOGY • Dominant allele: allele in a heterozygous individual that masks the other form of the trait • Designated by a CAPITAL letter ************************************** • Recessive allele: allele in heterozygous individual that is masked or hidden • Designated by lowercase form of same letter

  14. TERMINOLOGY • Homozygous: having identical alleles for a trait - EXAMPLES: PP or pp ************************** • Heterozygous: having different alleles for a trait - also called carriers - EXAMPLE: Pp

  15. TERMINOLOGY • Genotype: thecombination of alleles for a trait Letter combinationshows the alleles present in a gene - Indicates whether they are dominantor recessive , homozygous or heterozygous (e.g. PP, Pp, or pp) ********************* • Phenotype: the outward appearance of an organism - Indicates what is actually seen—tall or short, purple flower or white flower, etc.

  16. TERMINOLOGY • Punnett Square: chart used to show the probabilities of all the possible outcomes of a genetic cross • Shows the expected proportions of genotypes and phenotypes in a genetic cross • Essentially, a probability diagram

  17. TERMINOLOGY • Principle of segregation: states that two alleles for a trait separate during formation of gametes in meiosis • Result: each gamete carries only one allele for each trait

  18. The 2 alleles for a trait separate when gametes are formed Each gamete receives only one allele for the trait Offspring receive alleles separately from each parent After fertilization, the zygote will have a pair of alleles for each trait PRINCIPLE OF SEGREGATION

  19. Gametes for each parent are shown along the top & down the sides of Punnett square Note that the gametes separate or segregate outside the boxes Offspring (shown inside the boxes) receive one allele from each parent PUNNETT SQUARE: Tt x Tt

  20. TERMINOLOGY • Monohybrid cross: genetic cross in which parents differ in only one trait • EXAMPLE: Mendel crossed purple-flower pea plants with white flower pea plants • In this cross, the parent plants differ in only one (mono) trait

  21. MONOHYBRID CROSS

  22. Monohybrid cross: F1 generation: - homozygous tall x homozygous short - TT x tt - genotypic ratio: 4 : 0 - Tt - phenotypic ratio: 4 : 0 - tall MONOHYBRID CROSS:FIRST GENERATION (F1)

  23. Monohybrid cross: F2 generation: Cross between two F1 plants (Tt x Tt) - genotypic ratio: 1:2:1 - TT : Tt : tt - phenotypic ratio: 3:1 - tall : short MONOHYBRID CROSS: SECOND GENERATION (F2)

  24. CHANCE & PROBABILITY • Probability: the chance or possibility that a specific event may occur • Predicts what is likely to happen, not what must happen • Alleles occur in pairs for most traits • Offspring have an equal chance of receiving either one allele or the other for the trait from a parent—like tossing a coin

  25. CHANCE & PROBABILITY • Data from genetic crosses conforms to the rules of probability • Generally does not result in a perfect distribution • Like tossing a coin, each event is independent of all previous results.

  26. THE PRODUCT RULE • Product rule: the probability of independent events occurring together is the product of their individual probabilities • EXAMPLES: • Probability of a couple having a son is: ½ • Probability of a couple having two sons in a row is: ½ x ½ or ¼ • Probability of having 3 sons in a row is: ½ x ½ x ½ or 1/8

  27. PRINCIPLE OF INDEPENDENT ASSORTMENT • Principle that states that during gamete formation in an F2 cross, an allele for one trait can be paired with either of the two alleles for a different trait

  28. Meiosis: The Mechanism for Independent Assortment

  29. DIHYBRID CROSS • Genetic cross between two organisms that differ in two different traits

  30. DIHYBRID CROSS

  31. What is the genotype of an organism that displays the dominant phenotype? • Testcross: Procedure used to determine unknown genotype • Individual showing the dominant phenotype (whose genotype is not known) is mated with a homozygous recessive individual to determine unknown genotype

  32. Dominant phenotype (purple) is seen Is the genotype homozygous (PP) or heterozygous (Pp)??? Cross purple plant with unknown genotype with plant having recessive phenotype (white) TESTCROSS EXAMPLE

  33. TESTCROSS EXAMPLE

  34. Concept 10.3 THERE ARE MANY VARIATIONS OF INHERITANCE PATTERNS

  35. INTERMEDIATE INHERITANCE • Also called incomplete dominance • The pattern of inheritance in which the heterozygotes have a phenotype that is intermediate between the phenotypes of the two homozygotes • EXAMPLES: Andalusian chickens, snapdragon flowers

  36. INTERMEDIATE INHERITANCE • EXAMPLE: Cross a red-flowering snapdragon (CRCR) with a white flowering snapdragon (CWCW) • Show the phenotypic and genotypic ratios for both the F1 and F2 generations

  37. CRCR x CWCW F1 generation: - genotypes: all CRCW -phenotypes: all pink ****************** F2 generation: - genotypic ratio: 1:2:1 CRCR :CRCW :CWCW - phenotypic ratio: 1:2:1 red : pink : white INTERMEDIATE INHERITANCE

  38. CODOMINANCE & MULTIPLE ALLELIC INHERITANCE • Codominant alleles: phenotype of heterozygous individual is not intermediate  shows the separate distinct traits of both alleles • Multiple alleles: the existence of more than 2 alleles for a trait

  39. MULTIPLE ALLELIC INHERITANCE • NOTE: diploid individuals can only have two alleles for any trait that is controlled by a single gene • This results in multiple phenotypes for any trait thatis controlled by multiple alleles

  40. HUMAN BLOOD TYPE • Provides an example of both codominant and multiple allelic inheritance • 3 alleles exist for blood type: • Results in 4 different blood types • A, B, AB, and O

  41. 4 phenotypes for human blood: - A, B, AB, and O 3 alleles determine human blood type Two are codominant - IA and IB One is recessive – i IA and IB are both dominant to i HUMAN BLOOD GENOTYPES AND PHENOTYPES

  42. TRANSFUSION REACTIONS • Blood type must be known before transfusions are given • Antigens on RBCs react with proteins (antibodies) in foreign blood plasma causing them to clump • Clumping of RBCs of incompatible blood types can cause death

  43. Type O blood: universal donor blood Type O RBCs: no surface antigens—no clumping occurs Type AB blood: universal acceptor Type AB plasma has no antibodies BLOOD TRANSFUSIONS

  44. BLOOD TYPE CROSSES • Like any monohybrid cross:

  45. POLYGENIC INHERITANCE • Pattern of inheritance in which two or more genes affect a single trait • EXAMPLES: height, skin color, eye color, and hair color in humans

  46. Two or more genes affect one phenotype Usually involve quantitative alleles Continuous scale of measurement—bell curve—from one extreme phenotype to the other usually seen POLYGENIC INHERITANCE: SKIN COLOR

  47. POLYGENIC INHERITANCE: EYE COLOR

  48. ENVIRONMENTAL EFFECTS • Phenotypes in some cases are not rigidly defined by genotypes • Environmental factors can affect phenotype: • Temperature • Elevation • Sunlight • Nutrition • Activity • History of illnesses

  49. Concept 10.4 MEIOSIS EXPLAINS MENDEL’S PRINCIPLES

  50. CHROMOSOME THEORY OF INHERITANCE TWO MAIN POINTS: • 1. Genes are located on chromosomes • 2. Behavior of chromosomes during meiosis and fertilization accounts for inheritance patterns

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