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Chapter 11
• Genetics – the study of heredity
• Patterns of Inheritance
Copyright © 2006 Pearson Prentice Hall, Inc.
11.1 What Is the Physical
Basis of Inheritance?
• 11.1.1 Genes Are Sequences of
Nucleotides at Specific Locations on
Chromosomes
• 11.1.2 An Organism’s Two Alleles May
Be the Same or Different
– Figure 11.1 The relationships among
genes, alleles, and chromosomes (p. 168)
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chromosome 1
from tomato
pair of
homologous
chromosomes
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11.2 How Were the Principles
of Inheritance Discovered?
• Figure 11.2 Gregor Mendel (p. 168)
• 1860’s
• Studied pea plants – parents pass to
offspring the genetically heritable traits
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11.2 How Were the Principles
of Inheritance Discovered?
• 11.2.1 Doing It Right: The Secrets of
Mendel’s Success
– Figure 11.3 Flowers of the edible pea (p.
169)
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intact pea flower
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flower dissected to show
reproductive structures
Mendels Principles
• Alternative forms of genes exist (more than
1 color option etc.)
• 2 genes, 1 from each parent,
determines…thus each parent contributes 1
for a (new) combination of 2 (principle of
segregation)
• Dominant shows up first, what you
see/expressed (recessive, unseen but there,
i.e. masked)
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Genetics “terms”
•
•
•
•
Homozygous – same allele, “pure”
Heterozygous – diff. allele
Allele – alternatives forms of genes
Phenotype – physical characteristic
(seen/expressed)
• Wild Type – physical characteristic
(phenotype) seen most commonly in nature
• Genotype – genetic (chromosomal) make up
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11.3 How Are Single Traits
Inherited?
• 11_UN01 Mendel's Peas: F1
Generation (p. 169)
• 11_UN02 Mendel's Peas: F2
Generation (p. 170)
• In a mono-hybrid (X1) cross (only 1
characteristic differs at a time when
crossed)
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pollen
Parental
generation (P)
pollen
cross-fertilize
true-breeding,
purple-flowered
plant
true-breeding,
white-flowered
plant
First-generation
offspring (F1)
all purple-flowered
plants
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First
generation
offspring (F1)
self-fertilize
Second
generation
offspring (F2)
3/4 purple
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1/4 white
11.3 How Are Single Traits
Inherited?
• 11.3.1 The Pattern of Inheritance of Single Traits
Can Be Explained by the Inheritance of Alleles of a
Single Gene
– 11_UN03 Mendel's Peas: Gametes from a homozygous
parent (p. 170)
– 11_UN04 Mendel's Peas: Gametes from a heterozygous
parent (p. 171)
– 11_UN05 Mendel's Peas: Allele production (p. 171)
– 11_UN06 Mendel's Peas: Heterozygote offspring from
dominant and recessive parents (p. 171)
– 11_UN07 Mendel's Peas: F1 alleles to F2 generation (p. 171)
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More terms
• Hybrid cross – offspring of 2 diff.
varieties crossed. 1 = mono, 2= di
• P1 generation= parents
• F1 generation = offspring of P1
generation; next = F2
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homozygous parent
A
A
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gametes
A
A
heterozygous parent
A
a
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gametes
A
a
purple parent
P
PP
P
all P sperm and eggs
white parent
pp
p
p
all p sperm and eggs
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F1
offspring
sperm
eggs
P
p
Pp
P
Pp
or
p
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gametes from
F1 plants
F2
offspring
sperm
eggs
P
P
PP
P
p
Pp
p
P
Pp
p
p
pp
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11.3 How Are Single Traits
Inherited?
• 11.3.2 Simple “Genetic Bookkeeping”
Can Predict Genotypes and
Phenotypes of Offspring
– Figure 11.4 The Punnett square method
(p. 172)
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Pp
self-fertilize
p
1
—
2
1
—
eggs
1
—
p
2
P
2
1
—
PP
4
1
—
1
—
Pp
4
p
2
1
—
4
pP
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1
—
4
pp
2 results w/ a monohybrid cross
• 3:1 ratio phenotype
• 1:2:1 ratio genotype
• Look the same!
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11.3 How Are Single Traits
Inherited?
• 11.3.3 Mendel’s Hypothesis Can
Predict the Outcome of New Types of
Single-Trait Crosses
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Seed
shape
Seed
color
smooth
wrinkled
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
Pod
color
Flower
color
Flower
location
Plant
size
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11.4 How Are Multiple Traits
Inherited?
• 11.4.1 Mendel Concluded That Multiple
Traits Are Inherited Independently
– Figure 11.6 Predicting genotypes and
phenotypes for a cross between parents
that are heterozygous for two traits (p. 173)
– Figure 11.7 Independent assortment of
alleles (p. 174)
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What if 2 characteristics are
different?
• Di-hybrid cross
• 2 characteristics differ simultaneously…
• You get independent assortment –
separate out individually during gamete
formation, do not effect each other
• Result: 9:3:3:1 genotype
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SsYy
self-fertilize
eggs
1
—
4
1
—
4
SY
1
—
4
Sy
1
—
4
sY
1
—
4
sy
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SY
1
—
4
Sy
1
—
4
sY
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
1
—
16
sSYY
1
—
16
sSYy
1
—
16
ssYY
1
—
16
ssYy
1
— sSyy
Hall,16
Inc.
1
—
16
ssyY
1
—
16
ssyy
1
— sSyY
16 Prentice
Pearson
pairs of alleles on homologous
chromosomes in diploid cells
chromosomes replicate
replicate homologous
pair during metaphase
of meiosis I,
orienting like this
or like this
meiosis I
meiosis II
SY
sy
Sy
independent assortment produces four equally
likely allele combinations during meiosis
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sY
11.5 How Are Genes Located
on the Same Chromosome
Inherited?
• 11.5.1 Genes on the Same
Chromosome Tend to Be Inherited
Together
– 11_UN08 Pair of homologous
chromosomes (p. 175)
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flower color gene
pollen shape gene
purple
allele, P
long
allele, L
red
allele, p
round
allele, I
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11.5 How Are Genes Located
on the Same Chromosome
Inherited?
• 11.5.2 Crossing Over Can Create New
Combinations of Linked Alleles
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11.6 How Is Sex Determined?
• Figure 11.8 Photomicrograph of human
sex chromosomes (p. 175)
• Figure 11.9 Sex determination in
mammals (p. 176)
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Y chromosome
X chromosome
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female parent
eggs
male parent
female offspring
male offspring
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11.8 Do the Mendelian Rules
of Inheritance Apply to All
Traits?
• No!
• Incomplete Dominance Produces
Intermediate Phenotypes
– Figure 11.10 Incomplete dominance (p.
177)
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P:
Incomplete dominance =
Pink flowers,
a combo of
Red and white.
F1:
Thus heterozygous alleles
are
both dominant
and effect equally.
Phenotype +
Genotype =
F2:
1:2:1
1
—
2
1
—
RR
R´R´
RR´
RR´
R
2
1
R´
2
RR
4
1
1
—
R
—
—
eggs
1
—
RR´
4
R´
2
1
—
4
RR´
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1
—
4
R´R´
11.8 Do the Mendelian Rules
of Inheritance Apply to All
Traits?
• 11.8.2 A Single Gene May Have
Multiple Alleles
– Figure E11.1 Cystic fibrosis (p. 179)
– Table 11.1 Human Blood Group
Characteristics (p. 178)
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2 alleles effect 1 trait – codominance, both phenotypes expresseed
In heterozygous cross
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11.8 Do the Mendelian Rules
of Inheritance Apply to All
Traits?
• Other exceptions…
• 11.8.5 The Environment Influences the
Expression of Genes
– Figure 11.11 Environmental influence on
phenotype (p. 178)
– NATURE vs. NURTURE debates
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Others…
• Pleiotropy – 1 gene effects lots of
characteristics (sickle cell anemia)
• Polygenic inheritance – additive effect of 2+
genes = continuum, skin color
• Sex linked genes – (law of independent
assortment is not ALWAYS the case) i.e.
color blindness example (men)
• What can we do – amniocentisis, pedigree
charts…
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