Cytoplasmic Inheritance PDF

INTRODUCTION Cytoplasmic Male Sterility in Maize Male sterility is the failure of plants to produce functional anthers, pollen, or male gametes. Cytoplasmic male sterility, as the name indicates, is under extranuclear genetic control (under control of the mitochondrial or plastid genome...

INTRODUCTION Cytoplasmic Male Sterility in Maize Male sterility is the failure of plants to produce functional anthers, pollen, or male gametes. Cytoplasmic male sterility, as the name indicates, is under extranuclear genetic control (under control of the mitochondrial or plastid genomes). It shows non-Mendelian inheritance, with male sterility inherited maternally. In general, there are two types of cytoplasm: N (normal) and aberrant S (sterile) cytoplasm's. These types exhibit reciprocal differences. Cytoplasmic male sterility is an important part of hybrid maize production. The first commercial cytoplasmic male sterile, discovered in Texas, is known as CMS-T. The use of CMS-T, starting in the 1950s, eliminated the need for detasseling. In the early 1970s plants containing CMS-T genetics were susceptible to southern corn leaf blight and suffered from widespread loss of yield. Since then, CMS types C and S are used instead. Unfortunately, these types are prone to environmentally induced fertility restoration and must be carefully monitored in the field. Cytoplasmic male sterility (CMS) is a maternally inherited trait that causes dysfunctions in pollen and anther development. CMS is caused by the interaction between nuclear and mitochondrial genomes. A product of a CMS-causing gene encoded by the mitochondrial genome affects mitochondrial function and the regulation of nuclear genes, leading to male sterility. In contrast, the RESTORER OF FERTILITY gene (Rf gene) in the nuclear genome suppresses the expression of the CMS-causing gene and restores male fertility. The CMS/Rf system is an excellent model for understanding the genetic interactions and cooperative functions of mitochondrial and nuclear genomes in plants, and is also an agronomically important trait for hybrid seed production. INHERITANCE OF IOJAP TRAIT IN MAIZE Iojap is a condition which is found in maize. The name Iojap was derived from Iowa State (USA), the source of corn strain, japonica, the name of a striped variety. In corn the Iojap gene is recessive chromosomal gene which in homozygous condition produces green and white striped leaves on the plant. When a normal plant with green leaves (as female parent) is crossed to Iojap (as pollen parent) the offspring are green leaved.  Ij/Ij (Green) Female x ij/ij (iojap) Male Ij/ij (Green) In reciprocal cross between normal green (Male) and iojap (Female) plant there appear offspring's of three different types Ij/Ij (Green) Male x ij/ij (iojap) Female Ij/ij Ij/ij Green and Ij/ij White white Green Striped In iojap plants, green and white striped condition is inherited from female parent (maternal inheritance). It seems that in iojap plants, there occur two types of plastids; normal green and abnormal iojap plastids. During differentiation of female gametes plastids are randomly distributed in the egg cells: If the egg cells receives normal green plastids it will give rise to green leaved progeny irrespective of which plant as pollen parent. If the egg cells receives abnormal iojap colourless plastids, it after fertilization , will produce white leaved offspring. If the egg cell receives both normal green and abnormal iojap white plastids then after fertilization it will produce offspring with green and white striped leaves.