This document summarizes cytoplasmic or extra-nuclear inheritance. It discusses how cytoplasmic genes located in organelles like mitochondria and plastids can be passed from the female parent to offspring, since females contribute most of the cytoplasm during reproduction. Examples of cytoplasmic inheritance are provided, including variegated leaves in four o'clock plants inherited from the female parent's plastids, and the iojap trait in maize leaves inherited maternally from abnormal plastids. Cytoplasmic male sterility is also summarized, along with petite mutants in yeast related to aerobic respiration defects inherited from mitochondrial genes.

1. Department of Botany
Topic:-Cytoplasmic
Inheritance: Cellular
Organelles
Submitted to:- Prof. G.Kumar
Dr.Vaibhav Kumar
Dr. Ashwani Kumar
Submitted by:- Raman Shivhare
M.Sc. III Semester
2023-2024

2. Cytoplasmic Inheritance or Extra
nuclear Inheritance
 It is defined as the transmission of the genes that
occurs outside the nucleus.
 Inheritance due to genes located in cytoplasm
(plasma genes).
 Extra chromosomal inheritance defined as non
mendelian inheritance, usually involving DNA in
replicating mitochondria and some other organelles
of cell.
 Because female gametes contributes almost all of
the cytoplasm to the zygote and male gamete
contribute only nucleus , so the influence of
mothers extranuclear genotype on the phenotype
of the progeny is reffered to as maternal
inheritance or uniparental inheritance

3. ORGANELLAR INHERITANC
 Extra-nuclear inheritance is also associated with
certain cytoplasmic organelles (mitochondria,
plastids) that contain naked circular DNA and
protein synthesizing apparatus.

4. Plastid Inheritance in Variegated
Four “o” Clock Plant
 Plastid inheritance means the inheritance of plastid
characteristics due to plasma genes located in
plastids.
 Plastid inheritance was first described by C. Correns
(1908) in the four o’clock plant, Mirabilis jalapa.
 Leaves of Mirabilis jalapa may be green, white or
variegated and some branches may have only
green, only white or only variegated leaves.
Variegation means the presence of white or yellow
spots of variable size on the green background of
leaves.
 From various crosses of leaf phenotypes of Mirabilis
jalapa, clearly indicates that leaf phenotype of the
progeny is the same as that of the female parent.

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6. Inheritance of Iojap Trait in
Maize:
 In maize plant, iojap is a trait which produces green
and white stripped leaves.
 This trait is controlled by a recessive chromosomal
gene (ij) when present in homozygous state.
 The name iojap was derived from ‘Iowa’ state
(USA), the source of maize strain and japonica, the
name of a stripped variety.
 Iojap (ij) has been mapped by M.Rhoades (1946).
 When a normal plant with green leaves used as a
female parent is crossed with ioja parent, the
offspring will be green leaved Again, when a
reciprocal cross is made between a normal green

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 In iojap plants, green and white stripped trait of leaf is
inherited from the female parent due to maternal
inheritance. It seems that iojap plants contain two
types of plastids— normal green, and abnormal iojap
plastids.

8. Mitochondrial Inheritance
 Mitochondria contain their own DNA which may be
circular or linear.
 Haploid in nature . Mt.DNA contain g37 genes and
enclosed two types of rRNA and 22tRNA
Poky strains in Neurospora
 The best studt of poky strains of
Neurospora crassa first described by
Mitchell and Mitchell in 1952.
 A poky mutant differs from wild type
strains of N.crassa in the following

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 It is slow growing
 It shows maternal inheritance
 It has abnormal cytochrome(cyt a and b are absent
,only c present in excess while they all are present in
wild type)
 [poky] phenotype is inherited with the cytoplasm.

10. Cytoplasmic Male Sterility
 In maize and other plants ,cytoplasmic control of
male sterility is known .
 In such cases if the female parent is male
sterile(having plasmagene for male sterility),the f1
progeny would always be male sterile, because the
cytoplasm is mainly derived from the egg which is
obtain from the male sterile female parent.
 CMS is used in hybrid seed production in crops like
maize, jawar ,bajra etc.

11. Petite Mutant in Yeast
 Cells carrying a petite mutation grow slowly and
form tiny colonies on agar in contrast with the larger
ones of the wild phenotype
 These petites posses enzyme defects and are
deficient in aerobic respiration
TYPES OF PETITE MUTATION
1-segregational or nuclear petite
2-neutral petite
3-suppressive petite

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13. Clarification
 In neutral petite Almost whole population of cells
can be transformed into wild type
 No known mutagen can affect nuclear genes to
such an extent that all the population become
mutated.
 In suppressive petite If ascospore formation takes
place very soon after the zygote forms, it is found
that most of the asci will give a segregation of 0:4,
that is all the spores will give rise to petites.
 mtDNA of cytoplasmic petites has undergone
some sort of alteration.

14. Reference
 Genetics : Principle and Analysis – Daniel L. Hartl
& Elizabeth W. Jones
 Genetics : Dr.P.S. Verma & Dr. V.K. Agarwal
Thank you