Cytoplasmic Inheritance When inheritance of character is governed by cytoplasmic gene (plasmagene) rather than nuclear genes called cytoplas...
Cytoplasmic Inheritance
When inheritance of character is governed by cytoplasmic gene (plasmagene) rather than nuclear genes called cytoplasmic, extra-nuclear, extra-chromosomal, maternal inheritance.
Generally character from one generation to next generation inherit by nuclear genes.
Cytoplasmic inheritance was first time discovered by Correns in four ‘O’ Clcok (Mirabilis jalapa) in 1090.
Genes (DNA) responsible for cytoplasmic inheritance generally present in mitochondria (mt-DNA) and chloroplast (cp-DNA).
Features or characteristics of cytoplasmic inheritance -
Maternal Effect -
It is a inheritance or contribution of character only by the female parent not male parent.
In cytoplasmic inheritance, more cytoplasm having plasmagene comes from maternal side due to this some character only controlled by female parent.
Reciprocal differences -
Reciprocal differences means, Suppose when “A” as male parent crossed with “B” as female parent produces one character but when “B” as male parent crossed with “A” as female parent produces another character.
It is because of in one condition cytoplasm of parent which have plasmagene contributed in character formation while in another condition female parent does not have plasmagene for character contribution.
It not seen in nuclear gene inheritance.
None-Mendelian segregation -
In Mendelian inheritance a definite segregation pattern can be observe but in cytoplasmic inheritance, absence of typical segregation ration or pattern like 3:1 and 9:3:3:1.
Somatic Segregation -
Somatic segregation generally means segregation in somatic tissues.
In cytoplasmic inheritance variation exhibits in leaf (somatic tissue) which is rare in nuclear inheritance.
Controlled by plasmagenes -
In cytoplasmic inheritance character governed by cytoplasmic gene (plasmagene) like mitochondria and chloroplasts.
Mutagenesis -
Some mutagen like Ethidium bromide mutates only plasmagenes not nuclear genes.
Such mutagens describes the plasmagenes.
Parasitic infection -
Some traits transmitted by parasite, not considered as plasmagenes.
Plasmagenes not transmitted by parasites.
Difference between nuclear and cytoplasmic inheritance -
Sr. No. | Nuclear Inheritance | Cytoplasmic Inheritance |
1. | Controlled by nuclear genes | Controlled by cytoplasmic genes |
2. | Inheritance as Mendelian patter | Inheritance as non Mendelian patter. |
3. | In case of NI hereditary factor are genes. | In case of CI hereditary factor are plasmagenes. |
4. | Maternal effect not observed | Observed |
5. | Reciprocal differences not exhibits. | Exhibits |
6. | Mapping of gene is easy. | Difficult. |
7. | Shows complete and incomplete dominance. | Only female parent responsible for character expression. |
Sex-linked characters -
Sex liked character are those character which located on sex (X,Z) chromosome.
Gene located on such chromosomes are called sex linked gene.
Inheritance by such genes called sex linked inheritance.
Hemophilia, Baldness, Colour blindness in man and White eye, Vermilion eye are notable example of sex linked characters.
XcbXcb = Colour blind mother
XY = Normal father
X = Normal daughter because it have wild X allele from father and Xcb
From mother.
XcbY = Colour blind son.
Sex influenced character -
Sex influenced gene are those autosomal genes whose expression depends on the sex.
Character controlled by sex influenced gene is known as sex influenced character.
Inheritance of character by sex influenced gene is called as sex influenced inheritance.
Sex influenced character determine by the dominance of alleles in particular sex like allele responsible for baldness in man is dominant while recessive in female.
Expression of sex influenced character is determined by the hormonal process and hormones determined by alleles depend on the sex.
Baldness in human and horn in sheep is good example of sex influenced characters.
Sex limited characters -
Characters whose expression is limited in only one sex are known as sex limited character.
Gene and alleles responsible for the production of sex limited character are called as sex limited genes.
Generally gene express itself in both the sex but in certain gene express themself in only one sex while present in both sexes.
Its expression depends on sex hormone.
It also known as secondary character because it responsible for the development of secondary character.
Milk production in female is good example of sex limited characters, but male and female both have gene of milk production, unable express in male while well express in female.
Differences between sex linked, sex influenced and sex limited character -
Sr. No. | Sex linked | Sex limited |
1. | Located on sex (X,Z) chromosome. | Located on sex or autosome chromosome. |
2. | Can express in both sexes | Only in one sex. |
3. | Include character like - hemophilia, colour blindness which is not related to sex. | Include character related to sex like - milk production, beard in human being. |
UPSC Agriculture Optional Previous Year Questions Briefly describe the salient features of cytoplasmic inheritance, and give the reasons therefor. 2013 Sex-influenced and sex-limited characters. 2013 Sex expression in papaya. 2011 Briefly explain the salient features of cytoplasmic inheritance. 2001 What is sexlinked inheritance? How does it differ from Mendelian inheritance? Explain sex determination in Drosophila. 2000 Sexlimited characters2000 Critically discuss sex-linked, sex-limited and sex-influenced characters. . 1995 Distinguish between sexlinked, sexlimited and sexinfluenced characters. Give suitable examples. 1991 |
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