BIO207 Extranuclear/ Cytoplasmic/Organelle Inheritance

organelle inheritance

an organism’s phenotype is affected by the expression of genes contained in the DNA of the mitochondria or chloroplasts rather than the nucleus

basis of endosymbiotic theory

• mitochondria and chloroplasts have their own DNA in circular form with its size and structure lik prokaryotes; there are multiple copies of the genome per organelle

• have ribosomes that are more closely resemble those in prokaryotic cells

• codon usage is similar to prokaryotes

• reproduce by fission, independent of the rest of the cell

• rRNA sequences are similar to prokaryotes

95% of proteins are required for chloroplast function are synthesized from?

nuclear genome

99% of proteins required for mitochondrial function are synthesized from?

nuclear genome

why is the analysis of the inheritance pattern resulting from mutant alleles in chloroplasts and mitochondria more complex than Mendelian characters?

1) the function of these organelles is dependent on gene products from both nuclear and organelle DNA, making the discovery of the genetic origin of mutations difficult

2) many mitochondria and chloroplasts are present in each cell; thus, if only one or a few of the organelles contain a mutant gene in the cell among a population of mostly normal mitochondria, the corresponding mutant phenotype may not be revealed

what are the 3 reasons that cytoplasmic organelles, like mitochondria and chloroplast are most often inherited from one the mother?

1) in heterogamous species, the female gamete tends to be larger and has more cytoplasmic content and organelles than the male gamete

2) post fertilization, the female gametes provides most of the cytoplasm to the resulting zygote, while the male gametes provides only little more than a nucleus

3) a fertilization triggered autophagy event causes the selective degradation of paternal mitochondria immediately after fertilization

what is paternal leakage?

in a species with maternal inheritance, normally observed, occasionally the male parent may provide mitochondria to zygote

what did Karl Correns discover?

discovered a variant of the 4-o’clock plant, mirabilis jalapa, that had branches with either white, green or variegated leaves and this provided the earliest example of inheritance linked to chloroplast transmission

what did Corren’s conclude?

concluded that inheritance was transmitted through the cytoplasm of the maternal parent because the pollen, which contributes little or no cytoplasm to the zygote, had no apparent influence on the progeny phenotypes

what is cytoplasmic male sterility?

a condition under which a plant is unable to produce functional pollen

how is cytoplasmic sterility inherited?

it is maternally inherited that is often associated with mitochondrial mutations

how can CMS be restored?

it has been found that male fertility can be restored by nuclear-encoded fertility restorer (Rf) genes

what does sterility result from?

results from mitochondrial gene mutations causing cytoplasmic dysfunction

what does fertility restoration lie on?

relies on nuclear genes that suppress cytoplasmic function

what are the 2 types of petite mutations? describe each

1) segregational petite mutations - mutation in nuclear gene resulting in defective mitochondria; segregate in mendelian fashion; 2:2 ratio in unordered spores

2) vegetative petite mutations - mutations or deletions in mitochondrial DNA resulting in defective mitochondria; do not segregate as per normal mendelian fashion; show uniparental inheritance

what are the 2 categories of vegetative petite mutations?

1) neural petite mutations are outcompeted by wild-type, resulting in all normal colonies; lack most of their mitochondrial DNA

2) suppressive petite mutations outcompete wild-type, resulting in all petite colonies - lack small segments of mitochondrial DNA

what is one example of a human mitochondrial disease that shows maternal inheritance?

the phenotype is mitochondrial myopathy and the mutation is tRNA-Leu

what is mitochondrial replacement therapy?

1) the mother’s egg with faulty mitochondrial DNA is fertilized with the father’s sperm in a lab

2) nucleus carrying both parents’ genes is transplanted into the egg containing healthy mitochondrial DNA donated by another woman

3) the “reconstructed” embryo is then implanted into the moher and therefore the baby has 3 genetic parents