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Chapter 11

Chapter 11. Observing Patterns in Inherited Traits. Beginnings. Knew that two parents contributed hereditary material Thought it was blending of fluids But blending couldn’t explain some traits (a black horse and white horse should only produce gray horses). Gregor mendel.

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Chapter 11

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  1. Chapter 11 Observing Patterns in Inherited Traits

  2. Beginnings • Knew that two parents contributed hereditary material • Thought it was blending of fluids • But blending couldn’t explain some traits (a black horse and white horse should only produce gray horses)

  3. Gregormendel • Austrian Monk, mid-1800s • Math, physics, botany at University of Vienna • Studied Pisumsativum, garden pea plant • Self-fertilizes—produces both male & female gametes • Can cross-fertilize—done by plant breeders • Observed that white-flowered parent plants produce white flowers • Observed that when bred w/ different-colored plant, different traits emerged.

  4. Terms! • Genes—sequence of DNA on a chromosome that gives information on inheritable traits • Allele—all forms of the same gene • Hybrid—offspring of two “parents” who each breed true for different forms of a trait

  5. Terms! • Homozygous—identical alleles on homologous chromosomes • Heterozygous—non-identical alleles on homologous chromosomes • Dominant allele—masks effect of recessive allele when paired • Capital letter for dominant (“A”) • Lower-case letter for recessive (“a”)

  6. Terms! • Homozygous dominant—AA • Homozygous recessive—aa • Heterozygous—Aa • True-breeding parents—P • First-generation offspring—F1 • Second-generation offispring—F2 • Genotype—particular alleles in an individual • Phenotype—Individual’s observable traits

  7. Pea plant • Sperm in pollen grains, originate in stamen • Carpel—female flower part, has eggs, fertilization, seed development • Brush pollen onto carpel for artificial fertilization

  8. Monohybrid experiments • Mendel tracked 7 observable traits on pea plants • Seed shape (round or wrinkled) • Seed color (yellow or green) • Pod shape (inflated or wrinkled) • Pod color (green or yellow) • Flower color (purple or white) • Flower position (on stem or at tip) • Stem length (tall or dwarf) • Noted that F1 had all same trait, some of F2 had different trait • Approximately 3:1 ratio of traits

  9. Monohybrid experiments • Assume each P was homozygous • AA for one trait, aa for other trait • F1 only show “A” trait, not “a” trait • F2 show 1 “a” trait for every 3 “A” traits

  10. Mendel & Chromosomes

  11. Mendel & chromosomes • Dominant (A) genotype suppress recessive (a) phenotype

  12. Punnett square • Monohybrid cross

  13. Punnett square • Dihybrid cross

  14. Incomplete dominance • Heterozygous phenotype between the two homozygotes

  15. codominance • Nonidentical alleles expressed at same time • Multiple allele system—3 or more alleles for a single gene locus • Blood types

  16. Epistasis • Phenotype results from interaction among products of 2 or more gene pairs • Labrador retriever colors • B (black) & b (brown) • EE or Ee—melanin (pigment) production. Black or brown • ee—no melanin produced. Always yellow!

  17. Crossing over • Responsible for genetic variation • Can result in nonparental combinations • The closer the genes on a chromosome, the more likely to stay together

  18. Complex variation • Continuous variation—range of small differences in a trait • Due to polygenic inheritance—inheritance of multiple genes that affect the same trait • Eye color—due to different kinds & amounts of melanin

  19. Hint for exam…. • Review “Summary” & “Genetic Problems” on pages 182-185….some test questions there

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