Download Extranuclear Inheritance

Extranuclear Inheritance
Maternal Effects
Ÿ Phenotype of Offspring is determined (at least
in part) by mother’s nuclear genotype.
Ÿ Examples
w Early Development (later in semester)
w Limnaea (snail) Shell Coiling
Genotype of mother determines direction of
shell coiling of offspring.
w Humans:
ü Genomic Imprinting
Eggs are genomically imprinted, Sperm
are not. Prader-Willi syndrome vs
Angelman syndrome.
ü Uniparental disomies (both
chromosomes come from the same
parent
Organelle Heredity
Infectious Heredity
Organelle Heredity
Eukaryotic Organelles
Ÿ Chloroplast
Ÿ Mitochondria
Mitochondria
Structure
Ÿ Size: 16kb for Humans & other mammals
18kb for Xenopus & Drosophila
80kb for Yeast
500kb for Corn
Ÿ Shape: Circular, with supercoiling (like
Prokaryote)
Ÿ Replication:
w Normal DNA Replication Process
w Uses its own DNA polymerase
w Occurs at any time in the cell cycle
w Single origin of replication
Mitochondria -- Molecular Details
Ÿ Transcription
w Two Transcripts (one using the one strand as
the template, the other using the other strand
as the template).
w RNA polymerase is nuclear in origin
w mRNA genes are separated by tRNA genes
(used in processing)
w No Guanine Cap
w Poly-A tail is added (some genes use these
As for the final two nucleotides in the stop
codon UAA!)
Ÿ Translation
w mRNA is different from cytoplasmic
mRNA, so initiation is probably different
w fMet tRNA initiates translation
(Prokaryotic)
w Some genes are translated in the
Mitochondria, others are translated in the
cytoplasm.
w Some coding dictionary changes
Endosymbiont Theory of Evolution of
Mitochondria
Ÿ Mitochondria evolved from Prokaryotic
infection of the cell at some time during the
evolutionary development of Mitochondria
Ÿ Evidence:
w DNA is circular
w No nucleus
w Prokaryotic antibiotics effect organelle
chromsomes
w Eukaryotic antibiotics do not effect
organelle chromosomes
w rRNA in organelles are similar in sequence
to rRNA in Prokaryotes
Examples of Mitochondrial Traits
Ÿ Poky in Neurospora
w Slow growth due to defect in aerobic
respiration. This is due to a mutation in
cytochrome (a & b).
w cytoplasmically inherited
Ÿ Male sterility gene in Corn
Ÿ Petite gene in Saccharomyces
w Slow growth
w Not able to do aerobic respiration
w There is an interaction of the petites with
various genotypes in the nucleus
Ÿ Mitochondrial Myophathy in Humans
w Muscle Fatigue
w Unusually large mitochondria
Mitochondrial Eve
Ÿ Mitochondria is maternally derived in humans
Ÿ Males are Mitochondrial Dead ends
Ÿ Each individual has a single Mitochondrial
Line -- Mother to Maternal Grandmother to
Maternal-Maternal Great Grandmother, etc.
Ÿ Each generation, some Mitochondrial Lines
die out due to no females being born in that
line to carry on the mitochondria.
Ÿ Evenually, all lines converge to a single
female.
Ÿ Mutation rates can be used to estimate the
time of divergence, as well as the relationship
among the different subpopulations in the
world.
Infectious Heredity
Example
Kappa Particle in Paramecium
Ÿ Killer Strains
Ÿ Kappa Particle are bacterial strains living in
the cytoplasm of the Paramecium.