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CHAPTER 9

CHAPTER 9. FUNDAMENTALS OF GENETICS. MENDEL http://www.pbs.org/wgbh/nova/orchid/images/amat_mendel.jpg. GENETICS- field of biology devoted to understanding how characteristics are transmitted from parents to offspring - founded with the work of Gregor Johann Mendel, an Austrian monk

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CHAPTER 9

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  1. CHAPTER 9 FUNDAMENTALS OF GENETICS

  2. MENDELhttp://www.pbs.org/wgbh/nova/orchid/images/amat_mendel.jpgMENDELhttp://www.pbs.org/wgbh/nova/orchid/images/amat_mendel.jpg GENETICS- field of biology devoted to understanding how characteristics are transmitted from parents to offspring - founded with the work of Gregor Johann Mendel, an Austrian monk - studied pea plants (1840s, 1850s)

  3. - Mendel trained in the field of statistics - this training would help him in his research on HEREDITY- transmission of characteristics from parents to offspring - Mendel is most famous for his work on garden peas

  4. MENDEL’S PEAS 7 CHARACTERISTICS OF PEA PLANTS: 1. Plant height - long or short stems 2. Flower position along stem - axial or terminal 3. Pod color - green or yellow 4. Pod appearance - inflated or constricted

  5. 5. Seed texture - smooth or wrinkled 6. Seed color - yellow or green 7. Flower color - purple or white - Mendel collected seeds from the plants, and then planted those seeds the next year

  6. http://www.howe.k12.ok.us/~jimaskew/bio/pea.gif

  7. Mendel observed several variations: - white-flowering plants grew from seeds of purple-flowering plants - some short plants grew from seeds of tall growing plants

  8. CONTROLLED POLLINATION POLLINATION- occurs when pollen grains produced in the male reproductive parts of a flower (ANTHERS) are transferred to female reproductive parts of a flower (STIGMA) 2 TYPES: 1. Self-pollination- pollen is transferred from anthers of a flower to the stigma of the same flower or same plant

  9. 2. Cross-pollination- involves flowers of 2 separate plants - pea plants normally reproduce by self-pollination Mendel was able to control the pollination of his plants - he removed the anthers from one flower and transferred the anther of a flower from one plant to the stigma of a flower on another plant

  10. http://www.science.siu.edu/plant-biology/PLB117/JPEGs%20CD/0518.JPGhttp://www.science.siu.edu/plant-biology/PLB117/JPEGs%20CD/0518.JPG

  11. MENDEL’S EXPERIMENTS Mendel began by growing plants that were pure for each trait  always produce offspring with that trait STRAIN- plants pure for a specific trait - Mendel produced strains by allowing plants to self-pollinate for several generations - he obtained 14 strains, one for each trait - called each strain a parental or P1 generation

  12. Mendel then cross-pollinated these strains - he transferred pollen from the anthers of a plant pure for one trait to the stigma of another plant pure for the contrasting trait - he then recorded the number of each type of offspring - he called the offspring of the P1 generation the F1 generation (first filial)

  13. - he allowed flowers from F1 to self pollinate and called the offspring the F2 generation

  14. OBSERVATIONS Mendel hypothesized that something within the pea plants controlled the characteristics that he observed - he called these controls FACTORS - he hypothesized that each trait was inherited by means of a separate factor (a pair for each trait for the characteristics that he was studying)

  15. RECESSIVE AND DOMINANT TRAITS - when Mendel crossed strains, one of the P1 traits did not appear in the F1 plants - that trait would reappear in the F2 plants - hypothesized that the trait that DID appear in the F1 plants was controlled by a DOMINANT factor because it dominated the other factor - the trait that did NOT appear was controlled by a RECESSIVE factor

  16. - a trait controlled by a recessive factor had no effect on an organism’s appearance when paired with a trait controlled by a dominant factor LAW OF SEGREGATION Mendel concluded that paired factors separate during the formation of gametes - each gamete receives only one factor of each pair

  17. - this law states that a pair of factors is segregated, or separated, during the formation of gametes LAW OF INDEPENDENT ASSORTMENT - Mendel crossed plants that differed in two characteristics (ex: flower color and seed color) - the traits produced by dominant factors do not always appear together

  18. - this law states that factors for different characteristics are distributed to gametes independently MOLECULAR GENETICS- study of the structure and function of chromosomes and genes - most of Mendel’s findings agreed with modern molecular genetics

  19. RECALL: - a chromosome is a thread-like structure made of DNA - a gene is the segment of DNA on a chromosome that controls a trait - since chromosomes occur in pairs, genes occur in pairs - alternative forms of genes are called ALLELES

  20. Letters are used to represent alleles: - capital letters represent DOMINANT alleles - lowercase letters represent RECESSIVE alleles Ex: Green pod color is dominant, it would be represented by G - yellow pod color is recessive, it would be represented by g - it doesn’t matter what letter is selected to represent an allele

  21. RECALL: - during meiosis, gametes receive one chromosome from each homologous pair of chromosomes - when gametes combine, the offspring receives one allele for a given trait from each parent

  22. GENETIC CROSSES

  23. GENOTYPE- genetic makeup of an organism - consists of the alleles that the organism inherits from its parents Ex: White flowers = pp (white is recessive) Purple flowers = PP or Pp PHENOTYPE- appearance of an organism as a result of its genotype Ex: Phenotype of pp is white flowers Phenotype of PP or Pp is purple flowers

  24. HOMOZYGOUS- both alleles of a pair are alike - may be homozygous dominant or recessive - PP or pp HETEROZYGOUS- 2 alleles in the pair are different - Pp

  25. PROBABILITY PROBABILITY- likelihood that a specific event will occur - may be expressed as a decimal, percentage, or fraction Probability = number of times an event is expected to happen ---------------------------------------------------------------------------------------------- number of opportunities for an event to happen

  26. In Mendel’s experiments, the dominant trait of yellow seed color appeared 6,022 times - recessive trait of green seed color appeared 2,001 times - total individuals was 6,022 + 2,001 = 8,023 - to find the probability that the dominant trait would appear in a similar cross: 6,022 = 0.75 or 75% or ¾ ----------- 8,023

  27. - probability that the recessive trait will appear in the F2 generation: 2,001 = 0.25 or 25% or ¼ ------- 8,023 - fractions can also be expressed as ratios: ¼ = 1:4 - results predicted by probability are more likely to occur when there are many trials

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