Transcript AP Biology Chapter 15 Guided Notes

LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Chapter 15
The Chromosomal Basis of
Inheritance
Lectures by
Erin Barley
Kathleen Fitzpatrick
© 2011 Pearson Education, Inc.
Overview: Locating Genes Along
Chromosomes
• Mendel’s “hereditary factors” were __________
• Today we can show that genes are located on
_____________________
• The location of a particular gene can be seen
by tagging isolated chromosomes with a
______________________ that highlights the
gene
© 2011 Pearson Education, Inc.
Figure 15.1
Concept 15.1: Mendelian inheritance has its
physical basis in the behavior of chromosomes
• Mitosis and meiosis were first described in the
_______________
• The _____________________________ states:
– Mendelian genes have specific ________
(positions) on chromosomes
– Chromosomes undergo _______________ and
___________________________
• The behavior of chromosomes during
___________ can account for Mendel’s laws of
segregation and independent assortment
© 2011 Pearson Education, Inc.
Figure 15.2a
P Generation
Yellow-round
seeds (YYRR)
Y
Y
R R
r

y
y
r
Meiosis
Fertilization
Gametes
R Y
y
r
Green-wrinkled
seeds (yyrr)
Figure 15.2b
All F1 plants produce
yellow-round seeds (YyRr).
F1 Generation
R
y
r
R
y
r
Y
Y
LAW OF INDEPENDENT
ASSORTMENT Alleles of
genes on nonhomologous
chromosomes assort
independently during gamete
formation.
Meiosis
LAW OF SEGREGATION
The two alleles for each
gene separate during
gamete formation.
r
R
Y
y
r
R
Metaphase I
y
Y
1
1
R
r
r
R
Y
y
Anaphase I
Y
y
r
R
2
y
Y
Y
R
R
1/
4
YR
r
1/
4
yr
y
Y
Y
Y
y
r
R
2
y
Y
Gametes
r
Metaphase
II
r
r
1/
4
Yr
y
y
R
R
1/
4
yR
Figure 15.2c
LAW OF INDEPENDENT
ASSORTMENT
LAW OF SEGREGATION
F2 Generation
3 Fertilization
recombines the
R and r alleles
at random.
An F1  F1 cross-fertilization
9
:3
:3
:1
3 Fertilization results
in the 9:3:3:1
phenotypic ratio in
the F2 generation.
Morgan’s Experimental Evidence:
Scientific Inquiry
• The first solid evidence associating a specific
gene with a specific chromosome came from
___________________, an embryologist
• Morgan’s experiments with _______________
provided convincing evidence that
chromosomes are the location of Mendel’s
heritable factors
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Morgan’s Choice of Experimental Organism
• Several characteristics make fruit flies a
convenient organism for genetic studies
– They produce _____________________
– A generation can be bred every _____________
– They have only _____________ of chromosomes
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• Morgan noted _____________, or normal,
phenotypes that were common in the fly
populations
• Traits alternative to the wild type are called
_______________ phenotypes
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Figure 15.3
Correlating Behavior of a Gene’s Alleles
with Behavior of a Chromosome Pair
• In one experiment, Morgan mated male flies with
white eyes (_______) with female flies with red
eyes (_____________)
– The F1 generation all had ____________
– The F2 generation showed the _____ red:white
eye ratio, but only ___________ had white eyes
• Morgan determined that the white-eyed mutant
allele must be located on the ___ chromosome
• Morgan’s finding supported the chromosome
theory of inheritance
© 2011 Pearson Education, Inc.
Figure 15.4a
EXPERIMENT
P
Generation
F1
Generation
RESULTS
F2
Generation
All offspring
had red eyes.
Figure 15.4b
CONCLUSION
P
Generation
X
X
w
X
Y
w
w
Eggs
F1
Generation
Sperm
w
w
w
w
w
Eggs
F2
Generation
w
w
w
Sperm
w
w
w
w
w
w
Concept 15.2: Sex-linked genes exhibit
unique patterns of inheritance
• In humans and some other animals, there is a
chromosomal basis of ______________________
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The Chromosomal Basis of Sex
• In humans and other mammals, there are two
varieties of sex chromosomes: a larger ____
chromosome and a smaller __ chromosome
• Only the ________________________ have
regions that are homologous with corresponding
regions of the X chromosome
• The ________________ on the Y chromosome
codes for a protein that directs the development
of male anatomical features
© 2011 Pearson Education, Inc.
Figure 15.5
X
Y
• Females are ____, and males are _______
• Each ovum contains an ___ chromosome,
while a sperm may contain either an __ or a
___ chromosome
• Other animals have different methods of sex
determination
© 2011 Pearson Education, Inc.
Figure 15.6
44 
XY
44 
XX
Parents
22 
22 
X or Y
22 
X
Sperm
Egg
44 
XX
or
44 
XY
(a) The X-Y system Zygotes (offspring)
22 
XX
22 
X
76 
ZW
76 
ZZ
32
(Diploid)
16
(Haploid)
(b) The X-0 system
(c) The Z-W system
(d) The haplo-diploid system
• A gene that is located on either sex chromosome
is called a ________________
• Genes on the Y chromosome are called
________________; there are few of these
• Genes on the X chromosome are called
___________________
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Inheritance of X-Linked Genes
• X chromosomes have genes for many
characters unrelated to sex, whereas the Y
chromosome mainly encodes genes related
to ____________________
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• ___________________ follow specific patterns of
inheritance
• For a recessive ______________ to be expressed
– A female needs ________________ of the allele
(homozygous)
– A male needs only _______________ of the allele
(hemizygous)
• X-linked recessive disorders are much more
common in _____________ than in females
© 2011 Pearson Education, Inc.
Figure 15.7
XNXN
Sperm Xn
XNXn
XnY
Sperm XN
Y
XNY
XNXn
Sperm Xn
Y
XnY
Y
Eggs XN
XNXn XNY
Eggs XN
XNXN XNY
Eggs XN
XNXn XNY
XN
XNXn XNY
Xn
XNXn XnY
Xn
XnXn XnY
(a)
(b)
(c)
• Some disorders caused by recessive alleles on
the X chromosome in humans
– ___________________ (mostly X-linked)
– ____________________________
– ________________________
© 2011 Pearson Education, Inc.
X Inactivation in Female Mammals
• In mammalian females, one of the two X
chromosomes in each cell is ______________
_____________ during embryonic development
• The inactive X condenses into a ____________
• If a female is heterozygous for a particular gene
located on the X chromosome, she will be
_______________ for that character
© 2011 Pearson Education, Inc.
Figure 15.8
X chromosomes
Allele for
orange fur
Early embryo:
Two cell
populations
in adult cat:
Allele for
black fur
Cell division and
X chromosome
inactivation
Active X
Inactive X
Active X
Black fur
Orange fur
Concept 15.3: Linked genes tend to be
inherited together because they are located
near each other on the same chromosome
• Each chromosome has ________________
_______________ of genes (except the Y
chromosome)
• Genes located on the same chromosome that
tend to be inherited together are called
________________
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How Linkage Affects Inheritance
• Morgan did other experiments with fruit flies to
see how linkage affects inheritance of two
characters
• Morgan crossed flies that differed in traits of
______________________________
© 2011 Pearson Education, Inc.
Figure 15.9-1
EXPERIMENT
P Generation (homozygous)
Wild type
(gray body, normal wings)
Double mutant
(black body,
vestigial wings)
b b vg vg
b b vg vg
Figure 15.9-2
EXPERIMENT
P Generation (homozygous)
Wild type
(gray body, normal wings)
Double mutant
(black body,
vestigial wings)
b b vg vg
b b vg vg
F1 dihybrid
(wild type)
b b vg vg
TESTCROSS
Double mutant
b b vg vg
Figure 15.9-3
EXPERIMENT
P Generation (homozygous)
Wild type
(gray body, normal wings)
Double mutant
(black body,
vestigial wings)
b b vg vg
b b vg vg
F1 dihybrid
(wild type)
Double mutant
TESTCROSS
b b vg vg
b b vg vg
Testcross
offspring
Eggs b vg
b vg
Wild type
Black(gray-normal) vestigial
b vg
Grayvestigial
b vg
Blacknormal
b vg
Sperm
b b vg vg
b b vg vg
b b vg vg
b b vg vg
Figure 15.9-4
EXPERIMENT
P Generation (homozygous)
Wild type
(gray body, normal wings)
Double mutant
(black body,
vestigial wings)
b b vg vg
b b vg vg
F1 dihybrid
(wild type)
Double mutant
TESTCROSS
b b vg vg
b b vg vg
Testcross
offspring
Eggs b vg
b vg
b vg
Wild type
Black(gray-normal) vestigial
b vg
Blacknormal
Grayvestigial
b vg
Sperm
b b vg vg
b b vg vg
b b vg vg
b b vg vg
PREDICTED RATIOS
If genes are located on different chromosomes:
1
:
1
:
1
:
1
If genes are located on the same chromosome and
parental alleles are always inherited together:
1
:
1
:
0
:
0
965
:
944
:
206
:
185
RESULTS
• Morgan found that body color and wing size are
usually inherited _____________ in specific
combinations (________________________)
• He noted that these genes do not assort
independently, and reasoned that they were on
the ______________________________
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Figure 15.UN01
F1 dihybrid female
and homozygous
recessive male
in testcross
b+ vg+
b vg
b vg
b vg
b+ vg+
b vg
Most offspring
or
b vg
b vg
• However, ________________ were also produced
• Understanding this result involves exploring
________________________________, the
production of offspring with combinations of traits
differing from either parent
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Genetic Recombination and Linkage
• The genetic findings of Mendel and Morgan
relate to the chromosomal basis of
______________________
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Recombination of Unlinked Genes:
Independent Assortment of Chromosomes
• Mendel observed that combinations of traits in
some offspring __________ from either parent
• Offspring with a phenotype matching one of the
parental phenotypes are called ______________
• Offspring with nonparental phenotypes (new
combinations of traits) are called ____________
_________________________________
• A ____________ frequency of recombination is
observed for any two genes on different
chromosomes
© 2011 Pearson Education, Inc.
Figure 15.UN02
Gametes from yellow-round
dihybrid parent (YyRr)
Gametes from greenwrinkled homozygous
recessive parent (yyrr)
YR
yr
Yr
yR
YyRr
yyrr
Yyrr
yyRr
yr
Parentaltype
offspring
Recombinant
offspring
Recombination of Linked Genes: Crossing
Over
• Morgan discovered that genes can be linked,
but the linkage was ______________, because
some recombinant phenotypes were observed
• He proposed that some process must
occasionally break the physical connection
between genes on the same chromosome
• That mechanism was the ________________
of homologous chromosomes
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Animation: Crossing Over
Right-click slide / select”Play”
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Figure 15.10a
Gray body, normal wings
(F1 dihybrid)
Testcross
parents
Black body, vestigial wings
(double mutant)
b vg
b vg
b vg
b vg
Replication
of chromosomes
Replication
of chromosomes
Meiosis I
b vg
b vg
b vg
b vg
b vg
b vg
b vg
b vg
b vg
Meiosis I and II
b vg
b vg
b vg
Meiosis II
bvg
Eggs
Recombinant
chromosomes
b vg
b vg
b vg
b vg
Sperm
Figure 15.10b
Recombinant
chromosomes
Eggs
Testcross
offspring
bvg
965
Wild type
(gray-normal)
b vg
b vg
b vg
944
Blackvestigial
206
Grayvestigial
185
Blacknormal
b vg
b vg
b vg
b vg
b vg
b vg
b vg
b vg
Parental-type offspring
Recombinant offspring
Recombination
391 recombinants  100  17%

frequency
2,300 total offspring
b vg
Sperm
New Combinations of Alleles: Variation for
Normal Selection
• ____________________ chromosomes bring
alleles together in new combinations in gametes
• _____________________ increases even
further the number of variant combinations that
can be produced
• This abundance of genetic variation is the raw
material upon which ____________________
works
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Mapping the Distance Between Genes Using
Recombination Data: Scientific Inquiry
• Alfred Sturtevant, one of Morgan’s students,
constructed a _______________, an ordered
list of the genetic loci along a particular
chromosome
• Sturtevant predicted that the farther apart two
genes are, the higher the probability that a
___________________ will occur between
them and therefore the higher the
recombination frequency
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• A _________________ is a genetic map of a
chromosome based on recombination
frequencies
• Distances between genes can be expressed
as _____________; one map unit, or
centimorgan, represents a 1% recombination
frequency
• Map units indicate _____________________,
not precise locations of genes
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Figure 15.11
RESULTS
Recombination
frequencies
9%
Chromosome
9.5%
17%
b
cn
vg
• Genes that are far apart on the same
chromosome can have a recombination
frequency near _________
• Such genes are ______________ linked,
but _______________ unlinked, and
behave as if found on different
chromosomes
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• Sturtevant used recombination frequencies to
make linkage maps of fruit fly genes
• Using methods like ____________________,
geneticists can develop cytogenetic maps of
chromosomes
• _________________________ indicate the
positions of genes with respect to chromosomal
features
© 2011 Pearson Education, Inc.
Figure 15.12
Mutant phenotypes
Short
aristae
0
Long aristae
(appendages
on head)
Black
body
Cinnabar Vestigial
eyes
wings
48.5 57.5
Gray
body
Red
eyes
Brown
eyes
67.0
104.5
Normal
wings
Red
eyes
Wild-type phenotypes
Concept 15.4: Alterations of chromosome
number or structure cause some genetic
disorders
• Large-scale chromosomal alterations in
humans and other mammals often lead to
______________________ (miscarriages) or
cause a variety of _____________________
• ____________ tolerate such genetic changes
better than animals do
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Abnormal Chromosome Number
• In ______________, pairs of homologous
chromosomes do not separate normally
during meiosis
• As a result, one gamete receives ______
____________________ of chromosome,
and another gamete receives __________
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Figure 15.13-1
Meiosis I
Nondisjunction
Figure 15.13-2
Meiosis I
Nondisjunction
Meiosis II
Nondisjunction
Figure 15.13-3
Meiosis I
Nondisjunction
Meiosis II
Nondisjunction
Gametes
n1 n1 n1 n1
n1 n1
n
n
Number of chromosomes
(a) Nondisjunction of homologous chromosomes in
meiosis I
(b) Nondisjunction of sister
chromatids in meiosis II
• ________________ results from the
fertilization of gametes in which
nondisjunction occurred
• Offspring with this condition have an
__________________________ of a
particular chromosome
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• A ___________ zygote has only one copy of a
particular chromosome
• A ____________ zygote has three copies of a
particular chromosome
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• ______________ is a condition in which an
organism has more than two complete sets of
chromosomes
– ___________ (3n) is three sets of
chromosomes
– ___________ (4n) is four sets of
chromosomes
• Polyploidy is common in _________, but not
animals
• ____________ are more normal in appearance
than ____________________
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Alterations of Chromosome Structure
• Breakage of a chromosome can lead to four
types of changes in chromosome structure
– __________ removes a chromosomal segment
– ____________ repeats a segment
– ______________ reverses orientation of a
segment within a chromosome
– ________________ moves a segment from one
chromosome to another
© 2011 Pearson Education, Inc.
Figure 15.14a
(a) Deletion
A B C D E
F G H
A deletion removes a chromosomal segment.
A B C E
F G H
(b) Duplication
A B C D E
F G H
A duplication repeats a segment.
A B C B C D E
F G H
Figure 15.14b
(c) Inversion
A B C D E
F G H
An inversion reverses a segment within a
chromosome.
A D C B E
F G H
(d) Translocation
A B C D E
F G H
M N O P Q
R
A translocation moves a segment from one
chromosome to a nonhomologous chromosome.
M N O C D E
F G H
A B P Q
R
Human Disorders Due to Chromosomal
Alterations
• Alterations of chromosome number and
structure are associated with some serious
disorders
• Some types of ____________ appear to upset
the genetic balance less than others, resulting
in individuals surviving to birth and beyond
• These surviving individuals have a set of
symptoms, or ______________, characteristic
of the type of aneuploidy
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Down Syndrome (Trisomy 21)
• ____________________ is an aneuploid
condition that results from three copies of
chromosome 21
• It affects about one out of every 700 children
born in the United States
• The frequency of Down syndrome increases
with the ________________________, a
correlation that has not been explained
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Figure 15.15
Figure 15.15a
Figure 15.15b
Aneuploidy of Sex Chromosomes
• Nondisjunction of __________________
produces a variety of aneuploid conditions
• _____________________ is the result of an
extra chromosome in a male, producing _____
individuals
• _______________, called
________________, produces X0 females,
who are___________; it is the only known
viable monosomy in humans
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Disorders Caused by Structurally Altered
Chromosomes
• The syndrome __________ (“cry of the cat”),
results from a specific deletion in
____________________
• A child born with this syndrome is mentally
retarded and has a catlike cry; individuals
usually die in infancy or early childhood
• Certain cancers, including ____________
______________________ (CML), are
caused by translocations of chromosomes
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Figure 15.16
Normal chromosome 9
Normal chromosome 22
Reciprocal translocation
Translocated chromosome 9
Translocated chromosome 22
(Philadelphia chromosome)
Concept 15.5: Some inheritance patterns
are exceptions to standard Mendelian
inheritance
• There are two normal exceptions to Mendelian
genetics
• One exception involves genes located in the
____________, and the other exception
involves genes located outside the _________
• In both cases, the _____________________
contributing an allele is a factor in the pattern
of inheritance
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Genomic Imprinting
• For a few mammalian traits, the phenotype
depends on _____________ passed along the
alleles for those traits
• Such variation in phenotype is called
______________________
• Genomic imprinting involves the silencing of
certain genes that are “ ____________” with
an imprint during gamete production
© 2011 Pearson Education, Inc.
Figure 15.17a
Paternal
chromosome
Maternal
chromosome
Normal Igf2 allele
is expressed.
Normal Igf2 allele
is not expressed.
(a) Homozygote
Normal-sized mouse
(wild type)
Figure 15.17b
Mutant Igf2 allele
inherited from mother
Mutant Igf2 allele
inherited from father
Normal-sized mouse (wild type)
Dwarf mouse (mutant)
Normal Igf2 allele
is expressed.
Mutant Igf2 allele
is expressed.
Mutant Igf2 allele
is not expressed.
Normal Igf2 allele
is not expressed.
(b) Heterozygotes
• It appears that imprinting is the result of the
________________ (addition of —CH3) of
_______________ nucleotides
• Genomic imprinting is thought to affect only a
_____________________ of mammalian genes
• Most imprinted genes are critical for
________________________________
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Inheritance of Organelle Genes
• ______________________ (or cytoplasmic
genes) are found in organelles in the cytoplasm
• ________________________, and other
______ ___ carry small ___________ molecules
• Extranuclear genes are inherited ____________
because the zygote’s cytoplasm comes from the
egg
• The first evidence of extranuclear genes came
from studies on the inheritance of yellow or white
patches on leaves of an otherwise green plant
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Figure 15.18
• Some defects in ___________________
prevent cells from making enough ATP and
result in diseases that affect the muscular and
nervous systems
– For example, mitochondrial myopathy and
Leber’s hereditary optic neuropathy
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