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PASSAGE #30
Maternal inheritance is one pattern of inheritance which does not follow the rules of Mendelian genetics. It is an example of uniparental inheritance in which all progeny have the genotype and phenotype of the female parent.
Maternal inheritance can be demonstrated in the haploid fungus Neurospora by crossing the fungi in such a way that one parent contributes the bulk of the cytoplasm to the progeny. This cytoplasm-contributing parent is called the female parent, even though no true sexual reproduction occurs. The inheritance patterns of a mutant strain of Neurospora called poky have been studied using such crosses. Poky differs from the wild-type in that it is slow-growing and has abnormal quantities of cytochromes.
Investigators suspected that the poky mutation was carried in the mitochondria, instead of in the nuclear genome. The following experiments were designed to test this hypothesis.
Step 1:
Mitochondria were extracted from poky Neurospora mutants.
Step 2:
Using an ultrafine needle and syringe, these mitochondria were injected into wild-type Neurospora cells.
Step 3:
These recipient cells were cultured for several generations, and the phenotypes were examined.
Results:
The poky phenotype was observed in some of the cultured fungi.
The experiment supports which of the following conclusions?
A) The poky mutation resides in the mitochondria.
B) Poky mitochondria induce a genomic mutation which results in the poky phenotype.
C) Maternal inheritance does not apply to poky Neurospora mutants.
D) The slow growth of poky mutants increases their mutation rate.
The answer was "A"
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My initial answer would be A, since that was the logical point of the experiment. HOWEVER, I reexamined the results line, "The porky phenotype was observed in some of the cultured fungi" and thought that: Since only SOME of the phenotype was observed (NOT ALL), that would mean it could be another form of genetic inheritance, such as nuclear recessive gene, because maternal inheritance is supposed to result in 100% gene transfer in the mitochondria. Therefore, I chose C.
Am I wrong in my assumption that mitochondia gene transfer always results in 100% maternal phenotype in the progeny? The first paragraph in the passage even said"all progeny have the genotype and phenotype of the female parent."
Maternal inheritance is one pattern of inheritance which does not follow the rules of Mendelian genetics. It is an example of uniparental inheritance in which all progeny have the genotype and phenotype of the female parent.
Maternal inheritance can be demonstrated in the haploid fungus Neurospora by crossing the fungi in such a way that one parent contributes the bulk of the cytoplasm to the progeny. This cytoplasm-contributing parent is called the female parent, even though no true sexual reproduction occurs. The inheritance patterns of a mutant strain of Neurospora called poky have been studied using such crosses. Poky differs from the wild-type in that it is slow-growing and has abnormal quantities of cytochromes.
Investigators suspected that the poky mutation was carried in the mitochondria, instead of in the nuclear genome. The following experiments were designed to test this hypothesis.
Step 1:
Mitochondria were extracted from poky Neurospora mutants.
Step 2:
Using an ultrafine needle and syringe, these mitochondria were injected into wild-type Neurospora cells.
Step 3:
These recipient cells were cultured for several generations, and the phenotypes were examined.
Results:
The poky phenotype was observed in some of the cultured fungi.
The experiment supports which of the following conclusions?
A) The poky mutation resides in the mitochondria.
B) Poky mitochondria induce a genomic mutation which results in the poky phenotype.
C) Maternal inheritance does not apply to poky Neurospora mutants.
D) The slow growth of poky mutants increases their mutation rate.
The answer was "A"
---------------------------------------------------------------------
My initial answer would be A, since that was the logical point of the experiment. HOWEVER, I reexamined the results line, "The porky phenotype was observed in some of the cultured fungi" and thought that: Since only SOME of the phenotype was observed (NOT ALL), that would mean it could be another form of genetic inheritance, such as nuclear recessive gene, because maternal inheritance is supposed to result in 100% gene transfer in the mitochondria. Therefore, I chose C.
Am I wrong in my assumption that mitochondia gene transfer always results in 100% maternal phenotype in the progeny? The first paragraph in the passage even said"all progeny have the genotype and phenotype of the female parent."
