Concept of quantitative inheritance, Difference between qualitative and quantitative Traits, Inheritance of quantitative trait in Maize (Cob length), Cytoplasmic inheritance: Definition and concept, Chloroplast- Variation in Four O’clock plants, Mitochondria- Petite mutants in yeast

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September 27, 2020
Quantitative and Cytoplasmic
Inheritance
Dr. A. S. Wabale
Dr. A. S. Wabale
Assistant Professor and Research Guide
Assistant Professor and Research Guide
Post Graduate Department of Botany and Research Centre,
Post Graduate Department of Botany and Research Centre,
Padmashri Vikhe Patil College of Arts, Science and Commerce,
Padmashri Vikhe Patil College of Arts, Science and Commerce,
Pravaranagar
Pravaranagar-
- 413 713
413 713
dranilwabale78@gmail.com
dranilwabale78@gmail.com

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CONTENTS
CONTENTS
Ò Concept of quantitative inheritance, Difference between
qualitative and quantitative
Ò Traits, Inheritance of quantitative trait in Maize (Cob length),
Ò Cytoplasmic inheritance: Definition and concept, Chloroplast-
Variation in Four O’clock plants,
Ò Mitochondria- Petite mutants in yeast
Dr. A. S. Wabale
September 27, 2020

3. 3
Dr. A. S. Wabale
WHAT IS QUANTITATIVE INHERITANCE?
WHAT IS QUANTITATIVE INHERITANCE?
September 27, 2020
The inheritance of traits that are visible (such as colour of flower, shape of seed) refers to qualitative
inheritance and the traits that are detected only by measurements refers to quantitative inheritance.
Genetic inheritance of a character (such as human skin color) controlled by polygene is termed as
Quantitative inheritance. The quantitative traits such as height, weight, size, number of seeds and fruits are
usually controlled by multiple genes that have additive or cumulative effect. In quantitative inheritance,
each gene has a certain amount of effect and the more number of dominant genes, the more is the degree
of expression of the characters.
Quantitative inheritance was first studied by J. Kolreuter (1760) in tobacco (height). Nilsson-Ehle (1908) gave
first the experimental proof of polygenic inheritance in wheat kernel colour. It is considered that possible
origin of this type inheritance is due to duplication of chromosome or its parts, polyploidy or mutations
producing genes having similar effects.
Characters of Quantitative Inheritance
1. Quantitative Inheritance or polygenic inheritance deals with inheritance of quantitative characters
2. Each character is controlled by more than one pair of non-allelic genes
3. The number of intermediate types increases with the increase in the number of polygene, but the
number of parental types remains the same
4. Degree of expression depends on the number of dominant genes
5. Single effect gene cannot be seen and is influenced by environmental factors
6. F1 generation shows intermediate expression between the two parents
7. F2 generation with maximum individuals having intermediate genotype and phenotype

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WHAT MEANS LINKAGE?
WHAT MEANS LINKAGE?
Dr. A. S. Wabale
September 27, 2020
Qualitative inheritance Quantitative inheritance
• Deals with the inheritance of traits of kind. i.e.
Form, structure, colour etc.
• Deals with the inheritance of traits of degree.
i.e. heights or length, weight, number etc.
• Discontinuous variations occur • Continuous variations occur
• Each trait is controlled by two or many alleles
of a single gene
• Each trait is controlled by many non- allelic
genes
• The phenotypic expression of a gene is not
influenced by the environment
• The phenotypic expression of a gene is
influenced by the environment
• It is concerned with individual mating and
their progeny
• It is concerned with population of organisms
consisting of all possible kinds of mating
• It is analyzed by making counts and ratios • It is analyzed by statistical method
• They strictly follow Mendelian type of
inheritance
• They follow Johnson/Koelreuter type of
inheritance

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INHERITANCE OF COB LENGTH IN MAIZE
INHERITANCE OF COB LENGTH IN MAIZE
Dr. A. S. Wabale
September 27, 2020
R. A. Emerson and E. M. East in 1913 proposed a multiple gene hypothesis on inheritance of cob length in maize. They
crossed a variety Tom Thumb producing cobs of length ranging from 5-8.2cm (Average 6.6cm) with a variety Black Mexican
producing cobs of 11.6-22cm (Average 16.8cm). The F1 progeny were intermediate producing cobs with length ranging
from 9-15cm (Average 12.1cm)
F2 represented a wider variation than the F1 with some cobs as extreme in size as that of the parents. The
mean cob length in F2 varied from 6.6cm to 16.8cm falling into seven distinct phenotypic classes (6.6, 9.1, 11.7, 14.2 and
16.8cm) with a frequency of 1:4:6:4:1. The extreme phenotypes of the parents occurred in 1 out of 16 indicating that the
inheritance of cob length is controlled by two genes.
Let us explain this with an example. Assume that two genes (AABB) are active and each gene produces an
equal effect on the size of the cob, the individual contribution will be
Parents Tom Thumb (aabb) X Black Mexican (AABB)
Gametes ab AB
F1 Generation AaBb (2 X 2.55 + 6.6 = 11.7 cm)
Gametes AB Ab aB ab AB Ab aB ab
F2 Generation
Maximum height – Minimum Height
Number of alleles
Contribution of each allele = = 16.8 – 6.6/4 = 2.55 cm
AB Ab aB ab
AB AABB (16.8cm) AABb (14.2cm) AaBB (14.2cm) AaBb (11.7cm)
Ab AABb (14.2cm) AAbb (11.7cm) AaBb (11.7cm) Aabb (9.1cm)
aB AaBB (14.2cm) AaBb (11.7cm) aaBB (11.7cm) aaBb (9.1cm)
ab AaBb (11.7cm) Aabb (9.1cm) aaBb (9.1cm) aabb (6.6cm)
The F2 progeny produced 16 genotypes out of which
1/16 have 4 dominant alleles and thus produce cobs with 16.8 cm length.
4/16 have 3 dominant alleles and thus produce cobs with 14.2 cm length.
6/16 have 2 dominant alleles and thus produce cobs with 11.7 cm length.
4/16 have 1 dominant allele and thus produce cobs with 9.1 cm length.
1/16 have no dominant alleles and thus produce cobs with 6.6 cm length.

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Genes in the chromosomes have unquestionably been confirmed to be responsible for the
transfer of the variety of hereditary characters that are located in the nucleus. But new developments in
research reveals that inheritance of characters may also occur by some self- responsible or replicating bodies
like plastids and mitochondria that possess their own apparatus for synthesizing DNA and proteins present in
the cytoplasm and not in the chromosomes present in the nucleus.
This particular type of mechanism in which cytoplasmic particles take part in transmission of
characters from one generation to other refers to cytoplasmic inheritance. The total self reproducing
hereditary material of cytoplasm is termed as Plasmon like the genome (which refers to the total gene
complement of an haploid set of chromosomes) of chromosomes and such units of cytoplasmic hereditary
material are known as cytoplasmic genes or plasma-genes or Plasmon’s.
The cytoplasmic hereditary units are denoted by Greek letters-alpha, beta, gamma, sigma etc.
and on other hand the chromosomal genes are denoted by Roman letters- a, b, c, d and so on. It has been
understood that the cytoplasm in the sperm cell is very less as compared to the cytoplasm in the egg cell.
So, we could guess that plasma-genes mostly will be transmitted only through the egg cytoplasm
rather than minute sperm. This cytoplasmic inheritance can be studied with two best examples. i.e.
Chloroplast- Variation in Four O’clock plants and Mitochondria- Petite mutants in yeast
CYTOPLASMIC INHERITANCE: DEFINITION AND CONCEPT
CYTOPLASMIC INHERITANCE: DEFINITION AND CONCEPT
Dr. A. S. Wabale
September 27, 2020

7. CHLOROPLAST
CHLOROPLAST-
- VARIATION IN FOUR O’CLOCK PLANTS
VARIATION IN FOUR O’CLOCK PLANTS
7
The plant cytoplasm constitute minute bodies called plastids. Some of the plastids contain chlorophyll
pigment produced by chloroplastids. Others are colorless, produced by leucoplastids which are rich in starch.
Plastids look like genes in two respects (i) they are capable of multiplying by division and (ii) they are capable
of mutation.
Correns studied the plastid inheritance of plants in the four O’ clock plant (Mirabilis jalapa) in which the
leaves instead of normal green tissue are irregularly spotted with pale green or white patches. He found that
flowers from wholly green branches produce seeds that develop into normal plants. Flowers of variegated
plants yielded offspring's with leaves of 3 kinds viz., green, pale and variegated in various proportions.
Flowers from wholly white give progeny without chlorophyll. In each case the pollen has no influence on the
offspring. Inheritance was wholly maternal.
The colour of the offspring (Pale, green, pale-green and variegated) is determined by the egg and what the
egg produces, depends upon the characters of its plastids. Since plastids are found in the cytoplasm, one can
consider this as an example of cytoplasmic inheritance. Moreover, plastids are plasma genes since they have
the capacity of self duplication and mutation as that of the normal genes.
Dr. A. S. Wabale
September 27, 2020
Progeny of a variegated four ‘O’ clock plant

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Mitochondria are cytoplasmic organelles containing their own DNA and some enzymes that catalyze the
process of oxidative phosphorylation. Mitochondria are not autonomous bodies because they require their
own genes and nuclear genes to function normally.
The role of mitochondria in cytoplasmic inheritance was first understood when Ephrussi and his colleagues
(1955) studied petite mutants (petite meaning small) in yeast (Saccharomyces cerevisiae). When a cell
divides, approximately equal numbers of mitochondria pass into daughter cells. They can originate from
pre-existing mitochondria, and can probably divide transversely.
Ephrussi’s Experiment with Yeast:
Certain strains of yeast (s. cerevisiae) produce tiny colonies when grown on agar medium. Ephrussi (1953)
observed that one or two out of every one thousand colonies were only about one-third or one- half of the
diameter of the remainder. The small colonies are termed as petite colonies.
Cells from the normal large colonies, when spread on culture medium, further produced a small proportion
of petite colonies and this happened so time after time. The cells from the small colonies were true
breeding and they produced only petites.
Biochemical studies have established that the slow growth of petite colonies was due to the loss of aerobic
respiratory enzymes particularly cytochrome ‘a’ and ‘b’ and enzyme cytochrome oxidase occurring in
mitochondria of the cells and the utilization of the less efficient fermentation process by the cells.
The petite phenotype can result either from mutation of nuclear genes or from mitochondrial genes. Petite
mutants resulted due to mutation in a nuclear gene following Mendelian pattern of inheritance with
segregation occurring in heterozygotes.
This type of petite mutation is called segregational petite or nuclear petite. When the individuals of petite
colony are crossed to the individuals from normal large sized colony, normal zygotes are formed which
produce normal cells vegetatively.
When meiosis takes place in diploid cells, haploid cells are recovered that will form petite and normal
colonies in 1: 1 ratio as shown below:
MITOCHONDRIA
MITOCHONDRIA-
- PETITE MUTANTS IN YEAST
PETITE MUTANTS IN YEAST
Dr. A. S. Wabale
September 27, 2020

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When meiosis takes place in diploid cells, haploid cells are recovered that will form petite and normal
colonies in 1: 1 ratio as shown below:
Dr. A. S. Wabale
September 27, 2020
MITOCHONDRIA
MITOCHONDRIA-
- PETITE MUTANTS IN YEAST
PETITE MUTANTS IN YEAST

10. 10
1. Define Quantitative inheritance and comment on the concept of quantitative inheritance
2. Explain the characters of quantitative inheritance
3. Give the difference between qualitative and quantitative inheritance
4. Explain quantitative inheritance w.r.t cob length in maize
5. Define and describe the concept of cytoplasmic inheritance
6. Describe quantitative inheritance w.r.t Chloroplast- Variation in Four O’clock plants
7. Describe quantitative inheritance w.r.t Mitochondria- Petite mutants in yeast
June 27, 2020
ASSIGNMENT
Dr. A. S. Wabale