Mendel and the Gene Idea

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Chapter 14 Mendel and the Gene Idea
2
Vs.
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Fig. 14-1
Gregor Mendel
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Why the Garden Pea?
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Two fundamental principles of heredity

• Law of Segregation
• Law of Independent Assortment

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Two fundamental principles of heredity

• Law of Segregation
• Law of Independent Assortment

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Fig. 14-3-1
EXPERIMENT
P Generation (true-breeding parents)
?
Purple flowers
White flowers
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Fig. 14-3-2
EXPERIMENT
P Generation (true-breeding parents)
?
Purple flowers
White flowers
F1 Generation (hybrids)
All plants had purple flowers
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Fig. 14-3-3
EXPERIMENT
P Generation (true-breeding parents)
?
Purple flowers
White flowers
F1 Generation (hybrids)
All plants had purple flowers
F2 Generation
224 white-flowered plants
705 purple-flowered plants
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Mendels Four Hypotheses

• There are alternative forms of genes that account
  for variation
• alleles Alternative forms of the same gene

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Mendels Four Hypotheses (cont.)
2. For each characteristic, an organism inherits
two alleles, one from each parent Homozygous
Each allele is identical Heterozygous Each
allele is different
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Mendels Four Hypotheses (cont.)
3. If the alleles differ, only one contributes to
the organisms appearance Dominant allele
the one that contributes Recessive allele
the one that has no effect
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Mendels Four Hypotheses (cont.)
4. A sperm or egg only carries one allele for
each gene Law of Segregation the alleles
separate during gamete formation
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Fig. 14-4
Allele for purple flowers
Homologous pair of chromosomes
Locus for flower-color gene
Allele for white flowers
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Fig. 14-5-1
P Generation
Appearance
Purple flowers
White flowers
Genetic makeup
PP
pp
p
Gametes
P
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Fig. 14-5-2
P Generation
Appearance
Purple flowers
White flowers
Genetic makeup
PP
pp
p
Gametes
P
F1 Generation
Appearance
Purple flowers
Genetic makeup
Pp
Gametes
p
1/2
1/2
P
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Fig. 14-5-3
P Generation
Appearance
Purple flowers
White flowers
Genetic makeup
PP
pp
p
Gametes
P
F1 Generation
Appearance
Purple flowers
Genetic makeup
Pp
Gametes
p
1/2
1/2
P
Sperm
F2 Generation
p
P
P
PP
Pp
Eggs
p
Pp
pp
3
1
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Fig. 14-6
Phenotype
Genotype
PP
Purple
1
(homozygous)
Pp
Purple
3
(heterozygous)
2
Pp
Purple
(heterozygous)
pp
White
1
1
(homozygous)
Ratio 31
Ratio 121
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Table 14-1
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Two fundamental principles of heredity

• Law of Segregation
• Law of Independent Assortment

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Dihybrid Cross

• Predicting the results of two traits
• R Round peas
• r Wrinkled peas
• Y Yellow peas
• y Green peas
• RRYY x rryy ?

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Fig. 14-8a
EXPERIMENT
YYRR
yyrr
P Generation
Gametes
yr
YR
?
F1 Generation
YyRr
Hypothesis of dependent assortment
Hypothesis of independent assortment
Predictions
Sperm
or
Predicted offspring of F2 generation
yr
1/4
YR
Yr
yR
1/4
1/4
1/4
Sperm
yr
YR
1/2
1/2
1/4
YR
YYRR
YyRr
YYRr
YyRR
YR
1/2
YYRR
YyRr
Yr
1/4
Eggs
Yyrr
YyRr
YYRr
YYrr
Eggs
yr
1/2
YyRr
yyrr
yR
1/4
YyRr
YyRR
yyRR
yyRr
1/4
3/4
yr
1/4
Phenotypic ratio 31
yyRr
YyRr
Yyrr
yyrr
9/16
3/16
3/16
1/16
Phenotypic ratio 9331
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Fig. 14-8b
RESULTS
Phenotypic ratio approximately 9331
315
108
101
32
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Fig. 14-9
Rr
Rr
?
Segregation of alleles into sperm
Segregation of alleles into eggs
Sperm
1/2
1/2
R
r
R
R
R
1/2
r
R
1/4
1/4
Eggs
r
r
R
r
1/2
r
1/4
1/4
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Fig. 14-UN1
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Variations on Mendels Laws

• Incomplete Dominance
• Codominance
• Multiple Alleles
• Pleiotropy
• Epistasis
• Polygenic Inheritance
• Environmental Effects

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Variations on Mendels Laws

• Incomplete Dominance
• Codominance
• Multiple Alleles
• Pleiotropy
• Epistasis
• Polygenic Inheritance
• Environmental Effects

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Fig. 14-10-1
P Generation
Red
White
CRCR
CWCW
Gametes
CR
CW
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Fig. 14-10-2
P Generation
Red
White
CRCR
CWCW
Gametes
CR
CW
Pink
F1 Generation
CRCW
1/2
1/2
CR
CW
Gametes
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Fig. 14-10-3
P Generation
Red
White
CRCR
CWCW
Gametes
CR
CW
Pink
F1 Generation
CRCW
1/2
1/2
CR
CW
Gametes
Sperm
1/2
1/2
CR
CW
F2 Generation
1/2
CR
CRCW
CRCR
Eggs
1/2
CW
CRCW
CWCW
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Variations on Mendels Laws

• Incomplete Dominance
• Codominance
• Multiple Alleles
• Pleiotropy
• Epistasis
• Polygenic Inheritance
• Environmental Effects

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Fig. 14-11
IA
A
IB
B
i
none
(a) The three alleles for the ABO blood groups
and their associated carbohydrates
IAIA or IA i
A
B
IBIB or IB i
AB
IAIB
ii
O
(b) Blood group genotypes and phenotypes
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Variations on Mendels Laws

• Incomplete Dominance
• Codominance
• Multiple Alleles
• Pleiotropy
• Epistasis
• Polygenic Inheritance
• Environmental Effects

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Pleiotropy
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Variations on Mendels Laws

• Incomplete Dominance
• Codominance
• Multiple Alleles
• Pleiotropy
• Epistasis
• Polygenic Inheritance
• Environmental Effects

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Fig. 14-12
?
BbCc
BbCc
Sperm
1/4
1/4
1/4
1/4
BC
bC
Bc
bc
Eggs
1/4
BC
BBCc
BBCC
BbCC
BbCc
1/4
bC
BbCC
bbCC
BbCc
bbCc
1/4
Bc
BBcc
Bbcc
BBCc
BbCc
1/4
bc
BbCc
bbCc
Bbcc
bbcc
9
3
4
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Variations on Mendels Laws

• Incomplete Dominance
• Codominance
• Multiple Alleles
• Pleiotropy
• Epistasis
• Polygenic Inheritance
• Environmental Effects

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Fig. 14-13
?
AaBbCc
AaBbCc
Sperm
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8
1/8
Eggs
1/8
1/8
1/8
1/8
Phenotypes
1/64
6/64
15/64
20/64
15/64
6/64
1/64
Number of dark-skin alleles
2
6
0
1
3
4
5
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Variations on Mendels Laws

• Incomplete Dominance
• Codominance
• Multiple Alleles
• Pleiotropy
• Epistasis
• Polygenic Inheritance
• Environmental Effects

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Fig. 14-14
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Dominant vs. Wild Type
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Pedigree

• Scientists cannot control matings in humans
• So, they must gather as much information about a
  family history
• They organize it onto a family tree called a
  pedigree

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Fig. 14-15a
Key
Mating
Male
Affected male
Offspring, in birth order (first-born on left)
Female
Affected female
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Joshua Lambert
Abigail Linnell
John Eddy
Hepzibah Daggett
Abigail Lambert
Jonathan Lambert
Elizabeth Eddy
Dd
Female
Male
Deaf
Hearing
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Fig. 14-16
Parents
Normal
Normal
Aa
Aa
?
Sperm
a
A
Eggs
Aa
AA
Normal (carrier)
A
Normal
Aa
aa
Normal (carrier)
a
Albino
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Fig. 14-17
Parents
Dwarf
Normal
Dd
dd
?
Sperm
D
d
Eggs
dd
Dd
d
Dwarf
Normal
Dd
dd
d
Normal
Dwarf
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Fig. 14-18
Amniotic fluid withdrawn
Centrifugation
Fetus
Fetus
Suction tube inserted through cervix
Placenta
Placenta
Chorionic villi
Cervix
Uterus
Fluid
Bio- chemical tests
Fetal cells
Several hours
Fetal cells
Several hours
Several weeks
Several hours
Several weeks
Karyotyping
(b) Chorionic villus sampling (CVS)
(a) Amniocentesis
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