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第三章 Mendelian Genetics: How are Traits Inherited? 前言

第三章 Mendelian Genetics: How are Traits Inherited? 前言. 孟德爾對遺傳模式的洞察力 孟德爾( Gregor Mendel): 理性與感性的結合 數學與生物. 22. 7. 1822 in Hyncice - 6. 1. 1884 in Brno. Brno, Cze. Mendelianum. Lost of Mendel 1. The ignorance of comtemporary researchers:

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第三章 Mendelian Genetics: How are Traits Inherited? 前言

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  1. 第三章 Mendelian Genetics: How are Traits Inherited? 前言

  2. 孟德爾對遺傳模式的洞察力 孟德爾(Gregor Mendel): 理性與感性的結合 數學與生物 22. 7. 1822 in Hyncice - 6. 1. 1884 in Brno

  3. Brno, Cze

  4. Mendelianum

  5. Lost of Mendel 1. The ignorance of comtemporary researchers: W.O. Focke and Karl Nageli 2. Lack of knowledge of modern biology. 3. Astray by apomictic propagation 4. The rise of evolution theory emphazised on variations. 5. Personality of humility.

  6. Rediscovery of Mendel Hugo de Vries: Holland botanist Carl Correns: German botanist Erich Von Tschermak-Seysenegg: Autira botanist Wiiliam Bateson: English biologist, Second father of Genetics

  7. 純種系(True-breeding lineage) 雜種子代 (Hybrid off-springs) P 親代 F1第一子代 F2 第二子代

  8. F1 Results of One Monohybrid Cross

  9. F2 Results of Monohybrid Cross

  10. Mendel’s Monohybrid Cross Results 5,474 round 1,850 wrinkled 6,022 yellow 2,001 green 882 inflated 299 wrinkled 428 green 152 yellow F2 plants showed dominant-to-recessive ratio that averaged 3:1 705 purple 224 white 651 long stem 207 at tip 787 tall 277 dwarf

  11. 單一雜交(Mono-hybrid crosses)

  12. 預測單一雜交的結果 棋盤格法(Punnett-square method)

  13. 雙基因雜交(Di-hybrid crosses) Experimental cross between individuals that are homozygous for different versions of two traits

  14. A Dihybrid Cross - F1 Results purple flowers, tall white flowers, dwarf TRUE- BREEDING PARENTS: AABB x aabb GAMETES: AB AB ab ab AaBb F1 HYBRID OFFSPRING: All purple-flowered, tall

  15. F1 Results of Mendel’s Dihybrid Crosses • All plants displayed the dominant form of both traits • We now know: • All plants inherited one allele for each trait from each parent • All plants were heterozygous (AaBb)

  16. Phenotypic Ratios in F2 AaBbX AaBb • Four Phenotypes: • Tall, purple-flowered (9/16) • Tall, white-flowered (3/16) • Dwarf, purple-flowered (3/16) • Dwarf, white-flowered (1/16)

  17. ab ab aB AB AB Ab Ab aB Explanation of Mendel’s Dihybrid Results If the two traits are coded for by genes on separate chromosomes, sixteen gamete combinations are possible 1/4 1/4 1/4 1/4 1/4 1/16 1/16 1/16 1/16 AABB AABb AaBB AaBb 1/4 1/16 1/16 1/16 1/16 AABb AAbb AaBb Aabb 1/4 1/16 1/16 1/16 1/16 AaBB AaBb aaBB aaBb 1/4 1/16 1/16 1/16 1/16 AaBb Aabb aaBb aabb

  18. ab ab aB AB AB Ab Ab aB 16 Allele Combinations in F2 1/4 1/4 1/4 1/4 1/4 1/16 1/16 1/16 1/16 AABB AABb AaBB AaBb 1/4 1/16 1/16 1/16 1/16 AABb AAbb AaBb Aabb 1/4 1/16 1/16 1/16 1/16 AaBB AaBb aaBB aaBb 1/4 1/16 1/16 1/16 1/16 AaBb Aabb aaBb aabb

  19. Tremendous Variation Number of genotypes possible in offspring as a result of independent assortment and hybrid crossing is 3n (n is the number of gene loci at which the parents differ)

  20. Impact of Mendel’s Work • Mendel presented his results in 1865 • Paper received little notice • Mendel discontinued his experiments in 1871 • Paper rediscovered in 1900 and finally appreciated

  21. Do Mendel’s Laws Always Apply?

  22. Lethality affects the ratio of distribution

  23. 顯性關係 不完全顯性(Incomplete dominance) 共顯性(Codominance): 如,ABO血型是多重對偶基因系統 (Multiple allele system)

  24. ABO血型是多重對偶基因系統

  25. 單一基因的多重影響 既基因多效性(Pleiotropy) 如鐮刀型貧血症(Sickle-cell anemia)

  26. 鐮刀型貧血症(Sickle-cell anemia)

  27. 鐮刀型貧血症(Sickle-cell anemia)

  28. 基因對間的交互作用 如,上位現象(Epistasis) 例: 哺乳類的毛色 • Two genes involved • - One gene influences melanin production • Two alleles - B (black) is dominant over b (brown) • - Other gene influences melanin deposition • Two alleles - E promotes pigment deposition and is dominant over e

  29. Albinism • Phenotype results when pathway for melanin production is completely blocked • Genotype - Homozygous recessive at the gene locus that codes for tyrosinase, an enzyme in the melanin-synthesizing pathway

  30. 基因對間的交互作用 例:家禽的頭冠形狀

  31. 如何解釋較不易預期的變異 有關意外表現型 族群中連續變異

  32. 族群中連續變異 (Continuous variation) (line of bell-shaped curve indicates continuous variation in population) Number of individuals with some value of the trait Number of individuals with some value of the trait Range of values for the trait Range of values for the trait

  33. 環境影響表現型的例子 Temperature Effects on Phenotype • Himalayan rabbits are Homozygous for an allele that specifies a heat-sensitive version of an enzyme in melanin-producing pathway • Melanin is produced in cooler areas of body

  34. Environmental Effects on Plant Phenotype • Hydrangea macrophylla • Action of gene responsible for floral color is influenced by soil acidity • Flower color ranges from pink to blue

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