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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: - PowerPoint PPT Presentation
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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
GregorJ. Mendel, O.S.A., experimental garden (35x7 meters) in the grounds of the Augustinian Monastery in Old Brno.Itsappearance before 1922. Courtesy of Villanova University Archives.
The Monastery Garden with the greenhouse whichGregorJ. Mendel, O.S.A., had built in 1870. Its appearance
before 1902.Courtesy of Villanova University Archives.
Mendelianum
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.
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
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
F1 Results of One Monohybrid Cross
F2 Results of Monohybrid Cross
Mendel’s Monohybrid Cross Results
787 tall 277 dwarf
651 long stem
207 at tip
705 purple 224 white
152 yellow428 green
299 wrinkled882 inflated
6,022 yellow 2,001 green
5,474 round 1,850 wrinkled
F2 plants showed dominant-to-recessive ratio that averaged 3:1
單一雜交 (Mono-hybrid crosses)
預測單一雜交的結果
棋盤格法 (Punnett-square method)
雙基因雜交 (Di-hybrid crosses)Experimental cross between individuals
that are homozygous for different versions
of two traits
A Dihybrid Cross - F1 Results
AABB aabbx
AaBb
AB AB ab ab
TRUE-BREEDING PARENTS:
GAMETES:
F1 HYBRID OFFSPRING:
purple flowers, tall
white flowers,dwarf
All purple-flowered, tall
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)
Phenotypic Ratios in F2
Four Phenotypes:– Tall, purple-flowered (9/16)
– Tall, white-flowered (3/16)
– Dwarf, purple-flowered (3/16)
– Dwarf, white-flowered (1/16)
AaBb X AaBb
Explanation of Mendel’s Dihybrid Results
If the two traits are coded for by genes on separate chromosomes, sixteen gamete combinations are possible
aB
AB
AB
abAb
Ab
aB
ab
1/4
1/4
1/4
1/4
1/4 1/4 1/4 1/4
AaBb aabbAabb aaBb
AABB AABb AaBB AaBb
AABb AAbb AaBb Aabb
AaBb aaBB aaBbAaBB
1/161/161/161/16
1/161/161/161/16
1/161/161/161/16
1/16 1/16 1/16 1/16
16 Allele Combinations in F2
aB
AB
AB
abAb
Ab
aB
ab
1/4
1/4
1/4
1/4
1/4 1/4 1/4 1/4
AaBb aabbAabb aaBb
AABB AABb AaBB AaBb
AABb AAbb AaBb Aabb
AaBb aaBB aaBbAaBB
1/161/161/161/16
1/161/161/161/16
1/161/161/161/16
1/16 1/16 1/16 1/16
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)
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
Do Mendel’s Laws Always Apply?
Lethality affects the ratio of distribution
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)
ABO 血型是多重對偶基因系統
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)
鐮刀型貧血症 (Sickle-cell anemia)
鐮刀型貧血症 (Sickle-cell anemia)
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
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
基因對間的交互作用
例 : 家禽的頭冠形狀
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
族群中連續變異 (Continuous variation)
Range of values for the trait
Nu
mb
er o
f in
div
idu
als
wit
hso
me
valu
e o
f th
e t
rait
(line of bell-shaped curve indicates continuous variation in population)
Range of values for the traitN
um
ber
of
ind
ivid
ual
s w
ith
som
e va
lue
of
the
tra
it
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
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