Q.Extra nuclear inheritance is a consequence of presence of genes in

Cytoplasmic (extra-nuclear, extra-chromosomal) inheritance is inheritance governed by genes that lie outside the nucleus, carried instead in cytoplasmic organelles - specifically the mitochondrion and the chloroplast, each of which holds its own small, independent, self-replicating genetic unit called a plasmogene. It is classed as a form of non-Mendelian inheritance because it does not follow the ordinary segregation ratios of nuclear genes. Because the egg cell supplies almost all of a zygote's cytoplasm while the sperm or pollen contributes essentially only its nucleus at fertilisation, cytoplasmic traits are characteristically transmitted maternally - offspring resemble the female parent's phenotype for the trait, regardless of which direction a cross is made. This maternal signature, revealed by comparing a pair of reciprocal crosses, is the standard test used to tell a cytoplasmically inherited trait apart from an ordinary Mendelian (nuclear) one, which instead gives identical F1 results in both directions. Variegated leaf colour in Mirabilis jalapa (chloroplast inheritance) and cytoplasmic male sterility in pearl millet (mitochondrial inheritance) are the chapter's two worked examples of this pattern.