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Patterns of Inheritance
Chapter 12
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Early Ideas of Heredity
Classical
Male
Assumptions
Early Ideas of Heredity
Koelreuter
and Knight
and female contributions
Does
blending lead to uniformity of the
species? Why?
Fr. Gregor Mendel:
Modern Genetics
chromosome 1
from tomato
pair of
homologous
chromosomes
Color
Height
shape
1
Mendel and the Garden Pea
Advantages
intact pea flower
flower dissected to show
reproductive structures
of Garden Pea (4):
Mendel and the Garden Pea
Mendel’
Mendel’s
Experimental Design
Mendel’
Mendel’s Results
F1 Generation
(First Filial)
2
pollen
Mendel’
Mendel’s Results
Parental
generation (P)
pollen
F2 Generation
cross-fertilize
true-breeding,
purple-flowered
plant
(Second Filial)
true-breeding,
white-flowered
plant
First-generation
offspring (F1)
all purple-flowered
plants
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Firstgeneration
offspring (F1)
self-fertilize
A
A
A
A
Secondgeneration
offspring (F2)
homozygous parent
3/4 purple
gametes
1/4 white
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purple parent
P
PP
A
a
A
P
all P sperm and eggs
a
white parent
heterozygous parent
gametes
pp
p
p
all p sperm and eggs
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3
sperm
eggs
P
p
F2
offspring
gametes from
F1 plants
F1
offspring
sperm
eggs
P
P
PP
P
p
Pp
p
P
Pp
p
p
pp
Pp
or
p
Pp
P
Gametes from F1 can be…
Mendel’
Mendel’s Model of Heredity
Mendel’
Mendel’s Model of Heredity
Factors
2
Not
identical
Interpretation of Mendel’
Mendel’s
Results
Notational
Convention
Interpretation of Mendel’
Mendel’s
Results
F1
Generation
F2
Generation
Punnett
Squares
4
Pp
self-fertilize
1
2
P
1
2
eggs
p
Pp
self-fertilize
1 P
2
sperm
1
4
1
4
PP
1
2
Pp
P
1
2
eggs
p
1
p
2
sperm
1
4
pP
offspring
genotypes
eggs
1 P
2
1
2
P
1
4
1
P
2
1
2
p
1
4
Pp
1
2
P
1
4
pP
1
2
p
1
4
pp
genotypic
ratio
(1:2:1)
PP
P
1
2 P
eggs
offspring
genotypes
P
1
2
P
1
4
PP
1
2
P
1
2
p
1
4
Pp
1
2
P
1
2
P
1
4
1
2
P
1
2
p
1
4
1
4 Pp
1
4 pp
1
4 pP
1
4 pp
1
p
2
3
4 purple
1
white
4
genotypic
ratio
(1:2:1)
phenotypic
ratio
(3:1)
Mendelian Inheritance
Mendel’
Mendel’s
1
2
1
4 PP
1
4
PP
2
4
Pp
1
4
pp
3
4
purple
1
4
white
First Law of Heredity
pP
pp
pollen
Testcross
PP or Pp
sperm unknown
pp
all eggs p
if PP
if Pp
p
egg
all
sperm P
p
egg
1
P
2
all Pp
sperm
sperm
phenotypic
ratio
(3:1)
1
PP
4
2
4 Pp
1
2
1
P
2
pp
sperm
1
4
1 Pp
2
1
p
2
1
2 pp
5
Trait
Mendelian Inheritance
Mendel’
Mendel’s
Dominant form
smooth
wrinkled
Seed
color
yellow
green
inflated
constricted
green
yellow
purple
white
at leaf
junctions
at tips of
branches
tall
(1.8 to
2 meters)
dwarf
(0.2 to 0.4
meters)
Pod
shape
Second Law of Heredity
Recessive form
Seed
shape
Pod
color
Flower
color
Flower
location
Plant
size
SsYy
self-fertilize
SsYy
self-fertilize
eggs
sperm
1
4 SY
1
4 Sy
1
4 sY
1
4 sy
1
4
Sy
1
4
1
4 sY
sy
eggs
1
4 SY
1
16
SSYY
1
16
SSYy
1
16
SsYY
1
16
SsYy
1
16
SSyY
1
16
SSyy
1
16
SsyY
1
16
Ssyy
sSYY
1
16
sSYy
1
16
ssYY
1
16
ssYy
sSyY
1
16
sSyy
1
16
ssyY
1
16
ssyy
1
16
1
16
seed shape
seed color
1 SY
4
1 Sy
4
sperm
1
4 SY
1 sY
4
phenotypic ratio
(9:3:3:1)
smooth yellow
3
4
smooth x
3
4
yellow
=
9
16
3
4
smooth x
1
4
green
=
3
16
smooth green
1
4
wrinkled x
3
4
yellow
=
3
16
wrinkled yellow
1
4
wrinkled x
1
4
green
=
1
16
wrinkled green
1 sy
4
1
4
1
4
1 sY
4
Sy
sy
1
16 SSYY
1
16 SSYy
1
16 SsYY
1
16 SsYy
1
16 SSyY
1
16 SSyy
1
16 SsyY
1
16 Ssyy
1
16 sSYY
1
16 sSYy
1
16
ssYY
1
16 ssYy
1
16 sSyY
1
16 sSyy
1
16 ssyY
1
16 ssyy
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S
pairs of alleles on homologous
chromosomes in diploid cells
s
seed shape
seed color
phenotypic ratio
(9:3:3:1)
3
4 smooth
3
4
3
4 smooth
1
4 wrinkled
1
4 green
3
4 yellow
3
16 smooth green
3
16 wrinkled yellow
1
4 wrinkled
1
4
1
16 wrinkled green
y
chromosomes
replicate
replicated homologues
pair during metaphase
of meiosis I,
S
orienting like this
or like this
s
9
16 smooth yellow
yellow
green
Y
S
Y
s
y
y
Y
meiosis I
S
Y
s
y
S
y
s
Y
S
Y
s
y
S
y
s
Y
meiosis II
S
S
Y
SY
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s
Y
y
s
S
S
s
y
y
y
sy
Sy
independent assortment produces four equally
likely allele combinations during meiosis
s
Y
Y
sY
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6
flower color gene
flower color gene
pollen shape gene
pollen shape gene
sister
chromatids
purple
allele, P
long
allele, L
red
allele, p
round
allele, l
purple allele, P
homologous
chromosomes
(duplicated)
at meiosis I
long allele, L
sister
chromatids
red allele, p
round allele, l
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crossing
over
recombined
chromatids
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P
P
L
p
L
P
l
p
l
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L
S
pairs of alleles on homologous
chromosomes in diploid cells
s
Y
y
p
chromosomes
replicate
replicated homologues
pair during metaphase
of meiosis I,
orienting like this
or like this
L
S
Y
s
y
S
y
s
Y
meiosis I
P
l
S
Y
s
y
S
y
s
Y
S
Y
s
y
S
y
s
Y
meiosis II
S
p
l
S
Y
s
Y
SY
S
s
y
y
S
y
s
y
sy
Sy
independent assortment produces four equally
likely allele combinations during meiosis
s
Y
Y
sY
7
female parent
Sex determination
In mammals
Human Chromosomes
X1
somatic cells normally have
23 pairs of chromosomes.
X2
Human
eggs
X1
X1
male parent
Y
Xm
X2
Xm
Xm
sperm
Xm
X2
female offspring
X1
Y
X2
Y
Y
male offspring
Human Chromosomes
Mosaics.
Y chromosome
X chromosome
The Calico Cat
Chromosomes and Inheritance
SexSex-linkage
Thomas
Morgan
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8
female parent
XRXr
Phenotypic Considerations
r
R
XR Xr
R
Pleiotropic
r
Effects
eggs
XR
R
Xr
R
R
r
R
all the F2
females
have red eyes
male parent
XR Y
XR Y
XR XR
female offspring
XR
sperm
R
Y
R
half the F2
males
have red eyes,
half have white
eyes
r
XRY
male offspring
– Incomplete Dominance
Xr XR
Xr Y
P:
RR
If
F1:
RR′
F2:
1
2
1
2
R
1
4
1
4
RR′
1
2
R′
RR
1
4
RR’
RR′
1
4
R’R′
eggs
R
sperm
1
2
Incomplete Dominance
R′R′
R′
two wavywavyhaired people
marry, their
children could
have any of the
three hair types:
curly (C1C1),
wavy (C1C2), or
straight (C2C2)
Multiple Alleles: ABO Blood
Group
Codominance
– ABO Blood Groups
9
Phenotypic Considerations Which
Can Affect Mendelian Inheritance
Continuous
Variation (Polygenic
Inheritance)
R1R1′R2R2′
eggs
R1R2
R1R2′
R1′R2
R1′R2′
sperm
R1R2
R1R1′R2R2′
R1R1R2R2
R1R1R2R2 ′
R1R1′R2R2
R1R1′R2R2′
R1R1R2R2 ′
R1R1R2′R2′
R1R1′R2R2′
R1R1′R2′R2′
R1R1′R2R2
R1R1′R2R2 ′
R1′R1′R2R2
R1′R1′R2R2′
R1R1′R1R2′
R1R1′R2′R2′
R1′R1′R2R2′
R1′R1′R2′R2′
R1R2′
R1′R2
R1′R2′
Phenotypic considerations
– Environmental Effects
10
A pedigree for a dominant trait
How Are Human Genetic
Disorders Investigated?
I
II
III
A pedigree for a recessive trait
I
Family pedigrees
II
?
?
?
?
III
?
IV
?
?
How to read pedigrees
I, II, III = generations
= male
= female
= parents
= offspring
or
= shows trait
or
= does not show trait
or
= known carrier (heterozygote) for
recessive trait
? or ? = cannot determine genotype from pedigree
Human Gene Disorders
Human Gene Disorders
Gene
Human
Rattlesnake
Disorder
Wallaby
11
Soon to be Curable Defects?
Cystic
Fibrosis
Human Gene Disorders
– Not all defects are
recessive
Huntington’
Huntington’s
Disease
– Dominant lethal
– Delayed onset of
symptoms
– Trinucleotide
repeatrepeat-based
disorder
Human Gene Disorders
– SexSex-linked genetic diseases
I
maternal
grandfather
II
mother
aunts
father
III
sister
?
IV
G. Audesirk T. Audesirk
?
daughter
or
= colorblind
or
= normal color vision (not carrier)
= heterozygous carrier female,
normal color vision
12
Edward
Duke of Kent
Albert
Prince
of SaxeCoburg-Gotha
Edward VII
King of
England
unaffected male
hemophiliac male
unaffected female
carrier female
Abnormalities Due to
Chromosome Number
Primary
nondisjunction
Victoria
Princess of
Saxe-Coburg
Victoria
Queen
of England
Alexandra
of Denmark
Leopold
Duke
of Albany
Helen
Princess of
Waldeck-Pyrmont
Louis IV
Grand Duke of
Hesse-Darmstadt
Alice
Princess
of Hesse
several
unaffected
chidren
Beatrice
– Down Syndrome
Henry
Prince of
Battenburg
present British
royal family
(unaffected)
Victoria Elizabeth Alexandra
Mary
Tsarina
carrier
daughter
and
hemophiliac
grandson
Nicholas II Frederick Ernest Mary Irene
Victoria
of Russia
?
?
?
?
Olga
Tatiana
Maria
Anastasia
Alexander Alfonso
Albert
XII
Victoria Leopold Maurice
Queen
of Spain
?
Alexis
Tsarevitch
Alfonso
Crown
Prince
Juan
Beatrice
?
died Marie Jaime Gonzalo
in
infancy
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Nondisjunction in Sex
Chromosomes
X
Chromosome
Y
Chromosome
13
14