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Chapter
9
Extranuclear
Inheritance
Lecture Presentation by
Dr. Cindy Malone,
California State University Northridge
© 2015 Pearson Education, Inc.
Chapter 9: Introduction – Inheritance
 Observations revealed inheritance patterns fail
to reflect Mendelian principles
 Indicate apparent extranuclear influence on
phenotype
 Discovery of DNA in mitochondria and
chloroplasts; extranuclear inheritance is now
recognized as important aspect of genetics
© 2015 Pearson Education, Inc.
© 2015 Pearson Education, Inc.
Chapter 9: Extranuclear Inheritance
 Extranuclear inheritance
– Transmission of genetic information to offspring
through cytoplasm not nucleus
– Usually from one parent
 Varieties in extranuclear inheritance
– Organelle heredity
– Infectious heredity
– Maternal effect
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Chapter 9: Organelle Heredity
 Organelle heredity
– One variety of extranuclear inheritance
– DNA contained in mitochondria or chloroplasts
determines certain phenotypic characteristics of
offspring
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Chapter 9: Infectious Heredity
 Infectious heredity
– Variation of extranuclear inheritance
– Results from symbiotic or parasitic association
with microorganism
– Inherited phenotype affected by microbe in host’s
cytoplasm
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Chapter 9: Maternal Effect
 Maternal effect on phenotype
– Variation of extranuclear inheritance
– Nuclear gene products are stored in egg, then
transmitted through ooplasm to offspring
– Gene products in ovule distributed to embryo
cells – influence phenotype
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9.1 Organelle Heredity Involves DNA in
Chloroplasts and Mitochondria
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Section 9.1: Organelle Heredity
 Organelle heredity
– Involves DNA in chloroplast or mitochondria
– Inheritance of chloroplast or mitochondrial traits
often determined by phenotype of ovule source
(Figure 9-1)
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Section 9.1: Chloroplast Mutation
 Mirabilis jalapa (four o’clock plant)
– Plant has white, green, and variegated leaves
– Mutation in DNA housed in chloroplast
– Genetic defect eliminated green chlorophyll (lightabsorbing pigment within chloroplasts)
(Figure 9-1)
© 2015 Pearson Education, Inc.
© 2015 Pearson Education, Inc.
Figure 9-1
Section 9.2: DNA in Chloroplasts and
Mitochondria
 DNA in mitochondria and chloroplasts is unlike
DNA seen in nucleus of eukaryotic cells that
house these organelles
(Figures 9-6 and 9-7)
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Section 9.2: Endosymbiotic Theory
 Endosymbiotic theory (Lynn Margulis et al.)
– Mitochondria and chloroplasts (organelles)
arose independently 2 billion years ago from freeliving bacteria
– Organelles possessed attributes of aerobic
respiration and photosynthesis, respectively
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Section 9.2: Endosymbiotic Theory
 Main points of endosymbiotic theory
– Bacteria were engulfed by larger eukaryotic cells
– Beneficial symbiotic relationship developed
– Bacteria lost ability to function autonomously
– Eukaryotic cells gained oxidative respiration and
photosynthesis
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Section 9.2: mtDNA and cpDNA
 mtDNA: Mitochondrial DNA
– Exists in eukaryotes as double-stranded circular
DNA
– Smaller than DNA in chloroplasts
 cpDNA: Chloroplast DNA
– Genes encode products involved in
photosynthesis and translation
© 2015 Pearson Education, Inc.
Section 9.2: Ribosomal Variation
 Cytoplasm
– Ribosomes are uniformly 80S
 Mitochondria
– Ribosomes vary from 55S to 80S
 Chloroplasts
– Genes coding for rRNA (16S and 23S)
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Section 9.2: Mitochondrial Gene Products
 Majority of proteins for mitochondrial
function are encoded by nuclear genes
– DNA and RNA polymerase
– Initiation and elongation factors
– Ribosomal Proteins
– Aminoacyl tRNA synthetases
(Figure 9-8)
© 2015 Pearson Education, Inc.
© 2015 Pearson Education, Inc.
Figure 9-8
9.3 Mutations in Mitochondrial DNA Cause
Human Disorders
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Section 9.3: mtDNA in Humans
 Human mtDNA
– Contains 16,569 base pairs
– Coding for 13 proteins required for aerobic
cellular respiration
– Disruption of mitochondrial genes via mutation
has severe impacts on organism
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Section 9.3: mtDNA Mutations
 mtDNA susceptible to mutations
– No structural protection from histones
– DNA repair mechanism limited
– High concentrations of ROS (reactive oxygen
species) generated by cell respiration
 ROS is toxic—damages organelle contents (proteins,
lipids, mtDNA)
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Section 9.3: mtDNA Human Disorder
 Criteria for human disorder to be attributed to
mtDNA
– Inheritance must exhibit maternal inheritance
pattern
– Disorder must reflect deficiency in bioenergetic
function of organelle
– Must have mutation in one or more mitochondrial
gene
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Section 9.3: mtDNA Disorders
 Three disorders arising from mtDNA
– MERRF (myoclonic epilepsy and ragged-red fiber
disease)
– LHON (Leber’s hereditary optic neuropathy)
– KSS (Kearns–Sayre syndrome)
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Section 9.3: mtDNA Disorder: MERRF
 Myoclonic epilepsy and ragged-red fiber
disease
– Pattern of inheritance consistent with maternal
transmission
– Lack of muscular coordination
– “Ragged-red” skeletal muscle fibers
(Figure 9-9)
© 2015 Pearson Education, Inc.
Section 9.3: Mitochondria, Health, and Aging
 Mitochondrial dysfunction implicated in most
human diseases
– Anemia
– Blindness
– Type II diabetes
– Autism
– Infertility
– Neurodegenerative diseases: Parkinson and
Alzheimer
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Section 9.3: Prevention of mtDNA Disorders
 1 in 5000 humans have mtDNA-based disease or
are at risk for developing one
– Can be detected by genetic testing
– New therapies can prevent transmission of
mtDNA mutations to offspring
– Figure 9-10: Mitochondrial swapping in
oocytes
© 2015 Pearson Education, Inc.
© 2015 Pearson Education, Inc.
Figure 9-10
Section 9.4: Maternal Effect
 Maternal effect (maternal influence)
– Offspring’s phenotype is under control of nuclear
gene products present in egg
– Nuclear genes of female gamete transcribed;
genetic products accumulate in egg’s cytoplasm
– Products distributed among newly formed cells,
influencing patterns/traits established early in
development
© 2015 Pearson Education, Inc.
Section 9.4: Maternal Effect (Snails)
 Lymnaea peregra (snail)
– Shell coiling in Lymnaea peregra
– Example of maternal effect on permanent rather
than transitory phenotype
– Coiling pattern of progeny snails determined by
genotype of parent producing egg, regardless of
phenotype of parent
(Figure 9-11)
© 2015 Pearson Education, Inc.
© 2015 Pearson Education, Inc.
Figure 9-11