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Molecular Biology
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Genetics = Information Flow
Transmission Genetics =Classical Genetics = information flow between generations
Molecular Biology = Molecular Genetics = information flow within cells/organisms
DNA RNA Protein = THE CENTRAL DOGMA
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pea plant from green seed
Data of Goss (1824)
Xpea plant from yellow seed
All seeds yellow – grow and self fertilize
Some pods with allyellow seeds – grow into plants andself fertilize
Some pods with all seedsyellow, some with green and yellow seeds
Some pods with allgreen seeds
Many pods with both yellow and green seeds
Self fertilization ofplants grown from green
All progeny plants Have pods with green seeds only
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Data of Mendel (1866)
pea plant from green seed X
pea plant from yellow seed
All seeds yellow - Grow into plants and self fertilize(F1)First filial
generation
Count # of green and yellow seeds:- 8023 total seeds- 6022 yellow- 2001 green – grown into plants: self fertilization yields all green seeds
(F2)second filialgeneration
Take 519 yellow seeds – grown into plants: self fertilizationOf these 519 plants, 166 bred true (all yellow seeds), 353 did not (mixed yellow and green seeds)
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Mendel’s modelTrue breeding yellow AA
True breeding green aa
egg cells pollen cells
x
fertilize
Aa (yellow seeds) – grow into plants and self fertilizeF1
F2AA Aa
aA aa
(pollen)
(eggs)
A
A
a
a
3:1 yellow:green__________________¼ true breeding yellow½ “impure” yellow¼ true breeding green
aA
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Mendel’s First Law
Each trait is governed by 2 particles*, one inherited from each parent. These two particles do not influence each other in any way within an individual, but separate, uncontaminated in any way, into gametes at the time of reproductive cellFormation. (an unstated corollary is that any pollen cell can fertilize any egg cell = random fertilization).
Testing the law:- the test cross (Aa x aa) predicts new ratios- other traits tested
*Introduce modern terms: dominant, recessive, alleles, phenotype, genotype, heterozygote,homozygote
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Results of all Mendel's crosses in which parents differed for one character
Parental phenotype F1 F2 F2 ratio
1 . Round X wrinkled seeds All round 5474 round; 1850 wrinkled 2.96:1
2. Yellow X green seeds All yellow 6022 yellow; 2001 green 3.01:1
3. Purple X white petals All purple 705 purple; 224 white 3.15:1
4. Inflated X pinched pods All inflated 882 inflated; 299 pinched 2.95:1
5. Green X yellow pods All green 428 green; 152 yellow 2.82:1
6. Axial X terminal flowers All axial 651 axial; 207 terminal 3.14: 1
7. Long X short stems All long 787 long; 277 short 2.84: 1
What happens if two character traits are followed simultaneously?
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Fig. 13.16
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Mendel’s Second Law
Second Law=The Law of Independent Assortment:
During the formation of gametes, the segregation of alleles at one locus is independent of that of the segregation of alleles at any other.
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Mendel’s Second Law
The Law of Independent Assortment: During the formation of gametes, the segregation of alleles at one locus is independent of that of the segregation of alleles at any other.
Each trait is governed by 2 particles*, one inherited from each parent. These two particles do not influence each other in any way within an individual, but separate, uncontaminated in any way, into gametes at the time of reproductive cellFormation. (an unstated corollary is that any pollen cell can fertilize any egg cell = random fertilization).
Each trait is governed by 2 particles*, one inherited from each parent. These two particles do not influence each other in any way within an individual, but separate, uncontaminated in any way, into gametes at the time of reproductive cellFormation. (an unstated corollary is that any pollen cell can fertilize any egg cell = random fertilization).
Mendel’s First Law
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Genes’ (alleles’) eye view of meiosis and mitosis
A / a
A a
A aA a
chromosome (DNA) replicationduring S phase prior to mitosis
A a
A aA a
A a
A a
mitotic metaphaseanaphase, telophase,cytokinesis
A
a
A
a
A
abb
BB
B
b
aa
bb
AA B
B
genotype: Aa; Bb
Meiosis I metaphase
Meiosis I product cells
replication
Meiosis I anaphase,telophase, cytokinesis
aa
bb
AA B
B
Meiosis I product cells
A B
A B
a b
a b
Meiosis II product cells
Meiosis II anaphase,telophase, cytokinesis
Meiosis II metaphase
Meiosis II metaphase
AB
AB
ab
ab
aa
bb
AA
BB
Meiosis I product cells
A
B
A
a
a
b
Meiosis II products cells
Meiosis II anaphase,telophase, cytokinesis
Meiosis II metaphase
Meiosis II metaphase
b
B
Ab
Ab
aB
aB
Figure 2-30
Pseudoachondroplasia phenotype
Figure 2-26
Red-eyed and white-eyed Drosophila
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Eye Color Is a Sex-Linked Trait in Drosophila
female male female male
females males females males
white-eyed, normal-winged female x red-eyed, miniature winged male (wild type)
w+ mw m+
w m+
w m+
w+ m
wild type females w m+
white-eyed, normal-winged males
x
w m+
½ red-eyed, miniature winged
for male progeny, EXPECT:
w+ m
½ white-eyed, normal-winged
64% of males fell into above classes, but 36% were either wild typeOr doubly mutant !!!!!!!
w m+
w+ m
wild type females
genetic recombination = chromosomal crossing over
36% of chromosomes in meiosis I:
w m+
white-eyed, normal-winged males
x
w+ m+ w m
36% of males are either doubly mutant or wild type :
Figure 4-4Chiasmata are the sites of crossing over
Chiasmata visible inLocusta migratoria spermatogenesis
A synaptonemal complex
Chapter 4 OpenerA recombination-based map of one of the chromosomes of Drosophila
vermillion (v+ = red eyes, v = vermillion eyes)crossveinless (cv+ = normal wing veins, cv = missing crossveins)cut (c+ = normal wing margins, c = “snipped” wing margins)
v+. cv . ct x v . cv+ . ct+
v+/v . cv/cv+ . ct/ct+ x v/v . cv/cv . ct/ct (three point testcross)
phenotype # of progeny % of progeny recombinant v ..cv+ . ct+ 580 40% NRv+ . cv . ct 592 41% NRv .. cv . ct+ 45 3% v,cv ; cv,ctv+ . cv+ . ct 40 3% v,cv ; cv,ctv .. cv . ct 89 6% v,cv ; v,ctv+ . cv+ . ct+ 94 6% v,cv ; v,ctv ..cv+ . ct 3 0.2% v,ct ; cv,ctv+ . cv . ct+5 0.3% v,ct ; cv,ct
Phenotype # of progeny(T=1448) % of progeny recombinant v ..cv+ . ct+ 580 ~40% NRv+ . cv . ct 592 ~41% NRv .. cv . ct+ 45 ~3% v,cv ; cv,ctv+ . cv+ . ct 40 ~3% v,cv ; cv,ctv .. cv . ct 89 ~6% v,cv ; v,ctv+ . cv+ . ct+ 94 ~6% v,cv ; v,ctv ..cv+ . ct3 ~0.2% v,ct ; cv,ctv+ . cv . ct+ 5 ~0.3% v,ct ; cv,ct
v,cv recombinants: 45 + 40 + 89 + 94 = 268 = 18.5%v,ct recombinants: 89 + 94 + 3 + 5 = 191 = 13.2%ct,cv recombinants: 45 + 40 + 3 + 5 = 93 = 6.4%
Aha! The genes must all be on the same chromosome! (RF’s < 50%)
Hmmm…why is the measured distance between v,cv (18.5m.u.) less than the sum of the measured v,ct (13.2 m.u.) and ct,cv (6.4 m.u) distances(=19.6 m.u.)?
v ct cv13.2 m.u. 6.4 m.u.
double recombination
Hmmm…What is the expected # of double recombinants? A: 0.132 * 0.064 = .0084.0084 * 1448 = 12 expected double recombinantsBut… we got only 8 (3+5) Why?A: Interference! I = 1 - coefficient of coincidence (coc = o/e) = 0.33
v ct cv13.2 m.u. 6.4 m.u.
phenotype # of progeny % of progeny recombinant v ..cv+ . ct+ 580 ~40% NRv+ . cv . ct 592 ~41% NRv .. cv . ct+ 45 ~3% v,cv ; cv,ctv+ . cv+ . ct 40 ~3% v,cv ; cv,ctv .. cv . ct 89 ~6% v,cv ; v,ctv+ . cv+ . ct+ 94 ~6% v,cv ; v,ctv ..cv+ . ct3 ~0.2% v,ct ; cv,ct ; v,cv !!v+ . cv . ct+ 5 ~0.3% v,ct ; cv,ct ; v,cv !!
v,cv recombinants: 45 + 40 + 89 + 94 + 2(3+5) = 284 = 19.6%v,ct recombinants: 89 + 94 + 3 + 5 = 191 = 13.2%ct,cv recombinants: 45 + 40 + 3 + 5 = 93 = 6.4%
Aha! – we now realize the smallest classes of recombinants as doubles!
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Genetic Mapping
Mapping genes in humans involves determining the recombination frequency between a gene and an anonymous marker
Anonymous markers such as single nucleotide polymorphisms (SNPs) can be detected by molecular techniques.
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Testis Determining Factor (SRY)
Channel Flipping (FLP)
Catching and Throwing (BLZ-1)
Self Confidence (BLZ-2) - (note: unlinked to ability)
Addiction to Death and Destruction Films (T2)
Preadolescent fascination with Arachinida and Reptilia (MOM-4U)
Sitting on John Reading (SIT)
Selective Hearing Loss (HUH?)
Lack of Recall for Important Dates (OOPS)
Inability to Express Affection Over the Phone (ME-2)
Spitting (P2E)
New Genes Identified on the Human Y Chromosome
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• effects of recombination on chromosomes within a family
• siblings inherit different chromosome regions from their parents
• grandson inheritschromosome regions
from all four of hisgrandparents’chromosomes
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