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EXTRA CHROMOSOMAL INHERITANCE

Extrachromosomal inheritance involves the transmission of genetic traits from parent to offspring through cytoplasmic organelles like chloroplasts and mitochondria, rather than through nuclear genes. Three examples are given: (1) variegated leaves in four o'clock plants are inherited cytoplasmically, (2) streptomycin resistance in Chlamydomonas is inherited through chloroplasts, and (3) "poky" phenotype and abnormal cytochromes in Neurospora are inherited maternally through mitochondria. Cytoplasmic inheritance can also cause traits like cytoplasmic male sterility in plants. Maternal effects occur when the female parent's genotype influences offspring traits regardless of the male parent's genotype.

Education◦
EXTRA CHROMOSOMAL INHERITANCE Rupen Chakma 17/BBT/11 Amarjit Singh 17/BBT/29
CONTENTS • Introduction • Chloroplast inheritance - Variegation in Four o’clock plant - Chloroplast segregation in Chlamydomonas • Mitochondrial inheritance - Pokyness in Neurospora - Cytoplasmic male sterility • Maternal effects • Conclusion • Reference
Introduction  Extra nuclear inheritance is defined as non mendelian inheritance, which occurs when phenotype result from genetic influence other than the biparental transmission of genes located on chromosomes in the nucleus  The genes that have been called cytoplasmic genes, extrachromosomal genes, or extranuclear genes are located on a unique kind of chromosome inside cytoplasmic organelle  Commonly defined as transmission through the cytoplasm (or things in the cytoplasm, including organelles) rather than the nucleus
 Generally only one parents contributes organelle heredity  Organelles that contain chromosomes- Chloroplasts and mitochondria  Infectious heredity - Involves a symbiotic or parasitic association with a microorganism Maternal effect – When the expression of a character is influenced by the genotype of female parent
Variegation in Four O’clock plant  In 1909, Carl Correns used Mirabilis jalapa as a model study for his study on cytoplasmic inheritance.  Variants of Mirabilis jalapa in which some branches had white leave some had green leaves and some had variegated leaves
VARIEGATED LEAVES IN FOUR O’CLOCK PLANT
They maybe intercrossed in a variety of different combinations by transferring pollen from one flower to another
Segregation In chlamydomonas  Chlamydomonas is a single celled haploid green algae with a single chloroplast containing 50 to 100 genome  It as two mating type mt(+) and mt(- )which can fuse to form a diploid zygote
1/2mt+ 1/2mt- 1/2mt+ 1/2mt- All streptomycin resistance All streptomycin sensitiven
Pokyness in Neurospora  In 1952, Mary Mitchell isolated a mutant strain of Neurospora that she called poky.  Poky Neurospora is: -Slow growing -It shows maternal inheritance -It has abnormal amount of cytochromes
 It is possible to cross some fungi in such a way that one parent contributes the bulk of cytoplasm to the progeny and this cytoplasmic contributing parent is called female even though no true sex is involved  Maternal inheritance for the poky phenotype was established in the following crosses Poky(female) x wild type (male) → all poky Wild type (female) X poky (male) → all wild type
Cytoplasmic male sterility -CMS is a condition in which a plant does not produce functional pollen, but the female reproduction organs and fertility are normal. -Important in agriculture extensively used to produce hybrid corn seeds. -In 1930s, Rhoades demonstrated that male
-Male sterility is transmitted through the egg cytoplasm from generation to generation. -Rhoades pollinated the ears of male sterile strain with the pollen from a male fertile strain. -Repeated backcrossing of a male sterile variety, does not restore male fertility.
Maternal effects When the expression of a character is influenced by the genotype of female parent, it is referred to as maternal effects. Such characters exhibit clearcut differences in F1 for reciprocal crosses. Maternal effects are known in both plants and animals.
Coiling pattern of shell in snail  The effect of maternal genotype on the coiling behavior in snail was studied by Sturtevant.  The coiling behavior is controlled by a single gene.  In a cross between dextral female and sinistral male, it produces dextral snails in F1 as well as in F2.  But in a cross between sinistral female and dextral male, all the snails in F1 are sinistral and in F2 all the snails are dextral.
Conclusion Thus we know that not only nuclear inheritance is responsible for gene expression in an individual but cytoplasmic inheritance is also responsible for various characters.
REFERENCE • Principle of GENETICS by Eldon John Gardner, Michael J. Simmons, D. Peter Snustad • Genetics by Phudan singh
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