and Genes Inheritance
Chapter 15
The chromosomal basis of inheritance
Mendelian inheritence has its physical basis
Sexlinked genes exhibit unique paAerns of inheritance
AlteraCons of chromosome number or structure cause
geneCc disorders
Some inheritance paAerns are excepCons to standard
Mendelian inheritance
The Chromosomal Basis of Sex
In humans and some other animals, there is a
chromosomal basis of sex determinaCon
In humans and other mammals, there are two varieCes
of sex chromosomes: a larger X chromosome and a
smaller Y chromosome
A gene that is located on either sex chromosome is called
a sexlinked gene
Genes on the Y chromosome are called Ylinked genes;
there are few of these. Genes on the X chromosome are
called Xlinked genes
44 +
XY
44 +
XX
Parents
22 +
22 +
X or Y
22 +
X
Sperm
Egg
Females are XX, and males are XY
44 +
XX
or
X
44 +
XY
(a) The X-Y system Zygotes (offspring)
22 +
XX
22 +
X
76 +
ZW
Y
76 +
ZZ
(b) The X-0 system
Other animals have different methods
of sex determination
(c) The Z-W system
32
(Diploid)
(d) The haplo-diploid system
16
(Haploid)
Inheritance of XLinked Genes
X chromosomes have genes for many characters
unrelated to sex, whereas the Y chromosome mainly
encodes genes related to sex determinaCon
Xlinked genes follow specic paAerns of inheritance
For a recessive Xlinked trait to be expressed
A female needs two copies of the allele
(homozygous)
A male needs only one copy of the allele
(hemizygous)
Xlinked recessive disorders are much more common
in males than in females
Recombina*on of Genes:
Independent Assortment of genes in
Chromosomes
Mendel observed that combinaCons of traits in some
ospring dier from either parent
Recombina*on of Genes:
Independent Assortment of genes in
Chromosomes
Mendel observed that combinaCons of traits in some
ospring dier from either parent
Ospring with a phenotype matching one of the
parental phenotypes are called parental types
Ospring with nonparental phenotypes (new
combinaCons of traits) are called recombinant types,
or recombinants
A 50% frequency of recombinaCon is observed for any
two genes on dierent chromosomes
Abnormal Chromosome Number
one gamete receives
two of the same type of
chromosome, and
another gamete receives
no copy
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)
(b)
Nondisjunction of homo-logous
Nondisjunction of sister
chromosomes in meiosis I
chromatids in meiosis II
chromosomal alterations in humans and other mammals often lead to spontaneous
abortions (miscarriages) or cause a variety of developmental disorders
Aneuploidy of Chromosomes
Aneuploidy results from the ferClizaCon of gametes in
which nondisjuncCon occurred. Ospring with this
condiCon have an abnormal number of a parCcular
chromosome
NondisjuncCon of sex chromosomes produces a variety
of aneuploid condiCons
Klinefelter syndrome is the result of an extra
chromosome in a male, producing XXY individuals
Monosomy X, called Turner syndrome, produces X0
females, who are sterile; it is the only known viable
monosomy in humans
A trisomic zygote has three copies of a parCcular
chromosome
Down Syndrome (Trisomy 21)
aneuploid condition that results from
three copies of chromosome 21
AlteraCons of Chromosome Structure
(a) Deletion
ABC
DE
FG
H
A deletion removes a chromosomal segment.
ABC
E
FGH
(b) Duplication
ABC
DE
FG
H
A duplication repeats a segment.
ABC
BC
DE
FGH
(c) Inversion
ABC
DE
FGH
An inversion reverses a segment within a
chromosome.
ADC
BE
FGH
(d) Translocation
ABC
DE
FGH
MNO
PQ
R
A translocation moves a segment from one
chromosome to a nonhomologous chromosome.
MNO
CDE
FGH
A
BPQ
R
AlteraCons of Chromosome Structure
Breakage of a chromosome can lead to four
types of changes in chromosome structure
Dele9on removes a chromosomal segment
Duplica9on repeats a segment
Inversion reverses orientaCon of a segment
within a chromosome
Transloca9on moves a segment from one
chromosome to another
Disorders Caused by Structurally
Altered Chromosomes
Normal chromosome 9
Normal chromosome 22
Reciprocal
translocation
Translocated chromosome 9
Translocated chromosome 22
(Philadelphia chromosome)
The syndrome cri du chat (cry
of the cat), results from a
specic deleCon in
chromosome 5
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
chronic myelogenous leukemia
(CML), are caused by
translocaCons of chromosomes
Some inheritances are excepCons to
standard Mendelian inheritance
There are two normal excepCons to Mendelian geneCcs
One excepCon involves genes located in the nucleus,
and the other excepCon involves genes located outside
the nucleus
In both cases, the sex of the parent contribuCng an
allele is a factor in the paAern of inheritance
Inheritance of Organelle Genes
Extranuclear genes (or cytoplasmic genes) are found in
organelles in the cytoplasm
Mitochondria, chloroplasts, and other plant plasCds
carry small circular DNA molecules
Extranuclear genes are inherited maternally because
the zygotes cytoplasm comes from the egg
Some defects in mitochondrial genes prevent cells from
making enough ATP and result in diseases that aect
the muscular and nervous systems
For example, mitochondrial myopathy and Lebers
hereditary opCc neuropathy
DNA Technologies
Chapter 20
The DNA Toolbox
DNA sequencing has depended on advances in
technology, starCng with making recombinant DNA
In recombinant DNA, nucleoCde sequences from two
dierent sources, oaen two species, are combined in
vitro into the same DNA molecule
Methods for making recombinant DNA are central to
gene9c engineering, the direct manipulaCon of genes
for pracCcal purposes
DNA technology has revoluConized biotechnology, the
manipulaCon of organisms or their geneCc
components to make useful products
DNA cloning yields mulCple copies of
a gene or other DNA segment
To work directly with specic genes, scienCsts prepare
welldened segments of DNA in idenCcal copies, a
process called DNA cloning
Most methods for cloning pieces of DNA in the
laboratory share general features, such as the use of
bacteria and their plasmids
Plasmids are small circular DNA molecules that
replicate separately from the bacterial chromosome
Cloned genes are useful for making copies of a
parCcular gene and producing a protein product
DNA Cloning and Its ApplicaCons
Most methods for cloning pieces of DNA in the
laboratory share general features, such as the use of
bacteria and their plasmids
Plasmids are small circular DNA molecules that
replicate separately from the bacterial chromosome
Cloned genes are useful for making copies of a
parCcular gene and producing a protein product
DNA Cloning and Its ApplicaCons
Gene cloning involves using bacteria to make mulCple
copies of a gene
Foreign DNA is inserted into a plasmid, and the
recombinant plasmid is inserted into a bacterial cell
ReproducCon in the bacterial cell results in cloning of
the plasmid including the foreign DNA
This results in the producCon of mulCple copies of a
single gene
Bacterium
1 Gene inserted into
plasmid
Bacterial
Plasmid
chromosome
Recombinant
DNA (plasmid)
Cell containing gene
of interest
Gene of
interest
2 Plasmid put into
bacterial cell
DNA of
chromosome
(foreign DNA)
Recombinant
bacterium
3 Host cell grown in culture to
form a clone of cells containing
the cloned gene of interest
Protein expressed from
gene of interest
Gene of
interest
Protein harvested
Copies of gene
Basic
research
on gene
4 Basic research
and various
applications
Gene for pest
Gene used to alter
Protein dissolves
resistance inserted bacteria for cleaning blood clots in heart
into plants
up toxic waste
attack therapy
Basic
research
on protein
Human growth
hormone treats
stunted growth
Using RestricCon Enzymes to Make
Recombinant DNA
Bacterial restric9on enzymes cut DNA molecules at specic
DNA sequences called restric9on sites
A restricCon enzyme usually makes many cuts, yielding
restric9on fragments
The most useful restricCon enzymes cut DNA in a staggered
way, producing fragments with s9cky ends.
SCcky ends can bond with complementary sCcky ends of other
fragments
DNA ligase is an enzyme that seals the bonds between
restricCon fragments
Figure 20.3-3
Restriction site
5+
3+
GAATTC
CTTAAG
DNA
3+
5+
1 Restriction enzyme
cuts sugar-phosphate
backbones.
5+
3+
5+
G
CTTAA
5+ Sticky 3+
3+
end
2 DNA fragment added
from another molecule
cut by same enzyme.
Base pairing occurs.
5+
3+
3 DNA ligase
3+
AATTC
G
3+ 5+
G AATT C
C TTAA G
5+3+
5+
5+
3+
AATTC
G
G
CTTAA
3+
5+
3+ 5+
G AATT C
C TTAA G
5+ 3+
One possible combination
3+
5+
seals strands
5+
3+
3+
Recombinant DNA molecule
5+
Cloning a EukaryoCc Gene in a
Bacterial Plasmid
In gene cloning, the original plasmid is called a cloning
vector
A cloning vector is a DNA molecule that can carry
foreign DNA into a host cell and replicate there
FigureTECHNIQUE
20.4
Hummingbird cell
Bacterial plasmid
R gene
amp
lacZ gene
Restriction
site
Sticky
ends
Gene of
interest
Hummingbird DNA
fragments
Recombinant plasmids Nonrecombinant
plasmid
Bacteria carrying
plasmids
RESULTS
Colony carrying nonrecombinant plasmid
with intact lacZ gene
Colony carrying
recombinant
plasmid
with disrupted
lacZ gene
One of many
bacterial
clones
Figure 20.4b
Bacteria carrying
plasmids
RESULTS
Colony carrying nonrecombinant plasmid
with intact lacZ gene
Colony carrying
recombinant
plasmid
with disrupted
lacZ gene
One of many
bacterial
clones
Storing Cloned Genes in DNA Libraries
Foreign genome
Cut with restriction enzymes into either
small
or large
Bacterial artificial
fragments
fragments
chromosome (BAC)
Recombinant (b) BAC clone
plasmids
Large
insert
with
many
genes
Plasmid
clone
(a) Plasmid library
(c) Storing genome libraries
A genomic library that is made using bacteria is the collection of recombinant
vector clones produced by cloning DNA fragments from an entire genome
A genomic library that is made using bacteriophages is stored as a collection of
phage clones
Storing Cloned Genes in DNA Libraries
A complementary DNA (cDNA) library is made by
cloning DNA made in vitro by reverse transcripCon of
all the mRNA produced by a parCcular cell
A cDNA library represents only part of the genome
only the subset of genes transcribed into mRNA in the
original cells
Figure 20.6-5
DNA in
nucleus
mRNAs in
cytoplasm
Reverse
transcriptase Poly-A tail
mRNA
A A A A A A 3+
5+
3+
T T T T T 5+
DNA Primer
strand
A A A A A A 3+
T T T T T 5+
5+
3+
5+
3+
DNA
polymerase
5+
3+
3+
cDNA
5+
3+
5+
Amplifying DNA in Vitro: The
Polymerase Chain ReacCon (PCR)
The polymerase chain reac9on, PCR, can produce
many copies of a specic target segment of DNA
A threestep cycleheaCng, cooling, and replicaCon
brings about a chain reacCon that produces an
exponenCally growing populaCon of idenCcal DNA
molecules
The key to PCR is an unusual, heatstable DNA
polymerase called Taq polymerase.
Figure 20.8
5+
TECHNIQUE
3+
Target
sequence
Genomic DNA
1 Denaturation
3+
5+
5+
3+
3+
5+
2 Annealing
Cycle 1
yields
2
molecules
Primers
3 Extension
New
nucleotides
Cycle 2
yields
4
molecules
Cycle 3
yields 8
molecules;
2 molecules
(in white boxes)
match target
sequence
Expressing Cloned EukaryoCc Genes
Aaer a gene has been cloned, its protein product can
be produced in larger amounts for research
Cloned genes can be expressed as protein in either
bacterial or eukaryoCc cells
Cultured mammalian or insect cells may be used to
express and study proteins
DNA technology allows us to study the
expression, and funcCon of a gene
DNA cloning allows researchers to
Compare genes and alleles between individuals
Locate gene expression in a body
Determine the role of a gene in an organism
Several techniques are used to analyze the DNA of genes
One indirect method of rapidly analyzing and comparing genomes
is gel electrophoresis
This technique uses a gel as a molecular sieve to separate nucleic
acids or proteins by size, electrical charge, and other properCes
A current is applied that causes charged molecules to move
through the gel
Molecules are sorted into bands by their size
Figure 20.9a
TECHNIQUE
1
Mixture of
DNA molecules of
different
sizes
Power
source
- Cathode
Anode +
Wells
Gel
2
-
Power
source
+
Longer
molecules
Shorter
molecules
DNA gel electrophoresis
RESULTS
DNA gel electrophoresis
In restricCon fragment analysis, DNA fragments
produced by restricCon enzyme digesCon of a DNA
molecule are sorted by gel electrophoresis
RestricCon fragment analysis can be used to compare
two dierent DNA molecules, such as two alleles for a
gene, if the nucleoCde dierence alters a restricCon
site
VariaCons in DNA sequence are called polymorphisms
Sequence changes that alter restricCon sites are called
RFLPs (restric9on fragment length polymorphisms)
DNA gel electrophoresis
Normal -globin allele
175 bp
DdeI
Large fragment
201 bp
DdeI
Normal Sickle-cell
allele
allele
DdeI
DdeI
Large
fragment
Sickle-cell mutant -globin allele
376 bp
DdeI
Large fragment
DdeI
DdeI
(a) DdeI restriction sites in normal and
sickle-cell alleles of the -globin gene
201 bp
175 bp
376 bp
(b) Electrophoresis of restriction
fragments from normal and
sickle-cell alleles
Studying the Expression of
Interac*ng Groups of Genes
AutomaCon has allowed scienCsts to measure the
expression of thousands of genes at one Cme using
DNA microarray assays
DNA microarray assays compare paAerns of gene
expression in dierent Cssues, at dierent Cmes, or
under dierent condiCons
Figure 20.15
TECHNIQUE
1 Isolate mRNA.
2 Make cDNA by reverse
transcription, using
fluorescently labeled
nucleotides.
3 Apply the cDNA mixture to a
microarray, a different gene
in each spot. The cDNA hybridizes
with any complementary DNA on
the microarray.
Tissue sample
mRNA molecules
Labeled cDNA molecules
(single strands)
DNA fragments
representing a
specific gene
DNA microarray
4 Rinse off excess cDNA; scan microarray
for fluorescence. Each fluorescent spot
(yellow) represents a gene expressed
in the tissue sample.
DNA microarray
with 2,400
human genes
Determining Gene FuncCon
One way to determine funcCon is to disable the gene
and observe the consequences
Using in vitro mutagenesis, mutaCons are introduced
into a cloned gene, altering or destroying its funcCon
When the mutated gene is returned to the cell, the
normal genes funcCon might be determined by
examining the mutants phenotype
Gene expression can also be silenced using RNA
interference (RNAi)
SyntheCc doublestranded RNA molecules matching
the sequence of a parCcular gene are used to break
down or block the genes mRNA
Cloning organisms may lead to
producCon of stem cells for research
Organismal cloning produces one or more organisms
geneCcally idenCcal to the parent that donated the
single cell
One experimental approach for tesCng genomic
equivalence is to see whether a dierenCated cell can
generate a whole organism
A to9potent cell is one that can generate a complete
new organism
Plant cloning is used extensively in agriculture
Cloning Plants: SingleCell Cultures
Cross
section of
carrot root
2-mg
fragments
Fragments were
cultured in nutrient medium;
stirring caused
single cells to
shear off into
the liquid.
Single cells
free in
suspension
began to
divide.
Embryonic
plant developed
from a cultured
single cell.
Plantlet was
cultured on
agar medium.
Later it was
planted in soil.
Adult
plant
Cloning Animals: Nuclear TransplantaCon
In nuclear transplantaCon, the nucleus of an
unferClized egg cell or zygote is replaced with the
nucleus of a dierenCated cell
Experiments with frog embryos have shown that a
transplanted nucleus can oaen support normal
development of the egg
However, the older the donor nucleus, the lower the
percentage of normally developing tadpoles
Figure 20.18
EXPERIMENT Frog embryo
Frog egg cell
Frog tadpole
UV
Less differentiated cell
Fully differentiated
(intestinal) cell
Donor
nucleus
transplanted
Donor
nucleus
transplanted
Enucleated
egg cell
Egg with donor nucleus
activated to begin
development
RESULTS
Most develop
into tadpoles.
Most stop developing
before tadpole stage.
Reproduc*ve Cloning of Mammals
In 1997, Scojsh researchers announced the birth of
Dolly, a lamb cloned from an adult sheep by nuclear
transplantaCon from a dierenCated mammary cell
Dollys premature death in 2003, as well as her
arthriCs, led to speculaCon that her cells were not as
healthy as those of a normal sheep, possibly reecCng
incomplete reprogramming of the original transplanted
nucleus
Figure 20.19
TECHNIQUE
Mammary
cell donor
Egg cell
donor
1
Cultured
mammary
cells
2
Egg
cell from
ovary
3 Cells fused
4 Grown in culture
Nucleus
removed
Nucleus from
mammary cell
Early embryo
5 Implanted in uterus
of a third sheep
Surrogate
mother
6 Embryonic
development
RESULTS
Lamb (Dolly) genetically
identical to mammary cell donor
Stem Cells of Animals
A stem cell is a relaCvely unspecialized cell that can
reproduce itself indenitely and dierenCate into
specialized cells of one or more types
Stem cells isolated from early embryos at the
blastocyst stage are called embryonic stem (ES) cells;
these are able to dierenCate into all cell types
The adult body also has stem cells, which replace
nonreproducing specialized cells
Figure 20.21
Embryonic
stem cells
Adult
stem cells
Cells generating
some cell types
Cells generating
all embryonic
cell types
Cultured
stem cells
Different
culture
conditions
Different
types of
differentiated
cells
Liver
cells
Nerve
cells
Blood
cells
Stem Cells of Animals
Researchers can transform skin cells into ES cells by
using viruses to introduce stem cell master regulatory
genes
These transformed cells are called iPS cells (induced
pluripotent cells)
These cells can be used to treat some diseases and to
replace nonfuncConal Cssues
Figure 20.22
1 Remove skin cells
from patient.
2 Reprogram skin cells
so the cells become
induced pluripotent
stem (iPS) cells.
Patient with
damaged heart
tissue or other
disease
3 Treat iPS cells so
that they differentiate
into a specific
cell type.
4 Return cells to
patient, where
they can repair
damaged tissue.
PracCcal applicaCons of DNA technology
aect our lives in many ways
Medical applicaCon: One benet of DNA technology is
idenCcaCon of human genes in which mutaCon plays
a role in geneCc diseases
ScienCsts can diagnose many human geneCc disorders
using PCR and sequencespecic primers, then
sequencing the amplied product to look for the
diseasecausing mutaCon
PharmaceuCcal products: Advances in DNA technology
and geneCc research are important to the
development of new drugs to treat diseases
Human Gene Therapy
Gene therapy is the alteraCon of an aicted
individuals genes
Gene therapy holds great potenCal for treaCng
disorders traceable to a single defecCve gene
Vectors are used for delivery of genes into specic
types of cells, for example bone marrow
Gene therapy provokes both technical and ethical
quesCons
Figure 20.23
Cloned gene
1 Insert RNA version of normal allele
into retrovirus.
Viral RNA
Retrovirus
capsid
2 Let retrovirus infect bone marrow cells
that have been removed from the
patient and cultured.
3 Viral DNA carrying the normal
allele inserts into chromosome.
Bone
marrow
cell from
patient
4 Inject engineered
cells into patient.
Bone
marrow
PracCcal applicaCons of DNA technology
aect our lives in many ways
Synthesis of Small Molecules for Use as
Drugs
Protein Production in Cell Cultures
This is useful for the producCon of insulin, human
growth hormones, and vaccines
Forensic Evidence and Genetic Profiles
Protein Production by Pharm Animals
Protein Production by Pharm Animals
Transgenic animals are made by introducing genes from one
species into the genome of another animal
Transgenic animals are pharmaceuCcal factories, producers of
large amounts of otherwise rare substances for medical use
Environmental Cleanup
GeneCc engineering can be used to modify the metabolism of
microorganisms
Some modied microorganisms can be used to extract minerals
from the environment or degrade potenCally toxic waste
materials
Agricultural ApplicaCons
DNA technology is being used to improve agricultural
producCvity and food quality
GeneCc engineering of transgenic animals speeds up the
selecCve breeding process
Benecial genes can be transferred between varieCes or species
Figure 20.26
TECHNIQUE
Agrobacterium tumefaciens
Genetic engineering in plants has
been used to transfer many useful
genes including those for herbicide
resistance, increased resistance to
pests, increased resistance to salinity,
and improved nutritional value of crops
Ti
plasmid
Site where
restriction
enzyme cuts
T DNA
DNA with
the gene
of interest
RESULTS
Recombinant
Ti plasmid
Plant with new trait
Figure 20.UN04
Cloning
vector
DNA fragments from genomic DNA
or cDNA or copy of DNA obtained
by PCR
Mix and ligate
Recombinant DNA plasmids
Figure 20.UN06
Figure 20.UN07
Figure 20.UN08