14.2.1 Genetic Cross
Since DNA is present not only in the nucleus but also in mitochondria, whether the factor that determines senescence is in the nucleus or in the mitochondria can be determined from its mode of inheritance. When two parents are crossed, generally the cytoplasm (mitochondria) from the maternal (female) parent is transmitted to the progeny; rarely is there transfer of cytoplasm from the paternal parent (male). For example, in P. anserina, the cross (exceptional) non-senescent female X senescent male yielded non-senescent progeny, whereas the reciprocal cross senescent female X non-senescent male (exceptional) yielded senescent progeny. It was inferred that the senescence-determining factor is inside the mitochondria.
In the heterokaryon test, a heterokaryon is made between a senescent strain and a related nonsenescent strain by mixing and fusion of their germinating conidia or hyphal cells.
Wild-type cb aa3
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