4
Principles of
Inheritance
and Variation
It is a well-known fact that people with a known family history of Huntington's
disease are understandably concerned about whether they may pass the
Huntington gene on to their children. Advanced research in genetics has resulted
in early identi�cation of such genetic diseases where the embryos are tested for
the presence of Huntington gene, and only those testing negative for the
Huntington gene are implanted in the mother's uterus.
SELF-PRACTICE Q's
Introduced throughout the Chapter to self assess
your learning. Solutions of these unsolved Q's are
not in the book but given online via QR code.
Scan to download solutions
, MENDEL’S LAWS OF INHERITANCE 1
| TOPIC 1 |
MENDEL'S EXPERIMENT
Living organisms through the process of reproduction produce young
ones of their own kinds. Although the offsprings produced through
sexual reproduction resemble their parents and also each other. But still,
they show variations.
Genetics
It is the branch of biology that deals with the inheritance and variation
of characters from parents to offsprings.
Inheritance
It can be defined as the process of transmission of characters or traits
from parents to their progeny. Inheritance forms the basis of heredity.
Variation
It is defined as the degree by which the offsprings (progeny) differ from
their parents. Variations occur due to several reasons:
(1) Recombination of genes or crossing over.
(2) Reshuffling of genes/chromosomes.
(3) Mutation and environmental effects.
Humans have been exploiting the variations that were naturally present
in the wild populations of plants and animals to selectively breed and
select the organisms with desirable characters. This is done by artificial
selection and domestication from ancestral wild cows, e.g., well-known
Indian breed, Sahiwal cows in Punjab. Our ancestors knew about the
inheritance of characters and variations, but they have very little idea
about the scientific basis of these phenomena.
Gregor Johann Mendel is known as the “Father of genetics”. He was
the first one to conduct the experiments to understand the pattern of
inheritance and variations in living organisms.
2 Biology Class XII
Click here to access complete Educart book of Biology (Special Discount)
, Mendel chose garden pea (Pisum sativum) and conducted hybridisation
experiments on it for seven years (1856-1863) and proposed the ‘Laws
of Inheritance’ in living organisms.
In his experiments, Mendel performed artificial pollination/cross-
pollination with the help of emasculation (removal of anthers) using
several true breeding pea lines.
A true breeding line can be defined as the one which have undergone
continuous self-pollination and demonstrate the stable trait inheritance
and expression for several generations.
Mendel's Experimental Approach
(1) Mathematical logic and statistical analysis formed the basis of
Mendel’s methodology.
(2) Large sampling size of his experiments gave credibility to the data
which he collected.
(3) The inferences from his experiments on successive generations of
test plants showed that his results are in accordance to general rules
of inheritance rather than being unsubstantiated ideas.
Mendel's Experimental Background
Mendel selected garden pea – Pisum sativum for his experiments. The
reasons for adopting this plant were:
(1) Pea plants are annual plants with shorter life span.
(2) Flowers demonstrate self-pollination as the plant has bisexual
cleistogamous flowers (closed flowers), but cross-pollination is also
possible.
(3) Pea plant is easily available on a large scale.
(4) Pea plants can be easily grown and maintained.
(5) Pea plant has many distinct contrasting characteristics. The plants
show clearly distinct two opposing traits, e.g., tall or dwarf plants,
yellow or green seeds, etc.
Fourteen true-breeding pea plant varieties were selected by Mendel, as
pairs which were similar except for one character with contrasting traits.
The seven contrasting characteristics of garden pea plant studied by
Mendel were:
Principles of Inheritance and Variation 3
Click here to access complete Educart book of Biology (Special Discount)
Principles of
Inheritance
and Variation
It is a well-known fact that people with a known family history of Huntington's
disease are understandably concerned about whether they may pass the
Huntington gene on to their children. Advanced research in genetics has resulted
in early identi�cation of such genetic diseases where the embryos are tested for
the presence of Huntington gene, and only those testing negative for the
Huntington gene are implanted in the mother's uterus.
SELF-PRACTICE Q's
Introduced throughout the Chapter to self assess
your learning. Solutions of these unsolved Q's are
not in the book but given online via QR code.
Scan to download solutions
, MENDEL’S LAWS OF INHERITANCE 1
| TOPIC 1 |
MENDEL'S EXPERIMENT
Living organisms through the process of reproduction produce young
ones of their own kinds. Although the offsprings produced through
sexual reproduction resemble their parents and also each other. But still,
they show variations.
Genetics
It is the branch of biology that deals with the inheritance and variation
of characters from parents to offsprings.
Inheritance
It can be defined as the process of transmission of characters or traits
from parents to their progeny. Inheritance forms the basis of heredity.
Variation
It is defined as the degree by which the offsprings (progeny) differ from
their parents. Variations occur due to several reasons:
(1) Recombination of genes or crossing over.
(2) Reshuffling of genes/chromosomes.
(3) Mutation and environmental effects.
Humans have been exploiting the variations that were naturally present
in the wild populations of plants and animals to selectively breed and
select the organisms with desirable characters. This is done by artificial
selection and domestication from ancestral wild cows, e.g., well-known
Indian breed, Sahiwal cows in Punjab. Our ancestors knew about the
inheritance of characters and variations, but they have very little idea
about the scientific basis of these phenomena.
Gregor Johann Mendel is known as the “Father of genetics”. He was
the first one to conduct the experiments to understand the pattern of
inheritance and variations in living organisms.
2 Biology Class XII
Click here to access complete Educart book of Biology (Special Discount)
, Mendel chose garden pea (Pisum sativum) and conducted hybridisation
experiments on it for seven years (1856-1863) and proposed the ‘Laws
of Inheritance’ in living organisms.
In his experiments, Mendel performed artificial pollination/cross-
pollination with the help of emasculation (removal of anthers) using
several true breeding pea lines.
A true breeding line can be defined as the one which have undergone
continuous self-pollination and demonstrate the stable trait inheritance
and expression for several generations.
Mendel's Experimental Approach
(1) Mathematical logic and statistical analysis formed the basis of
Mendel’s methodology.
(2) Large sampling size of his experiments gave credibility to the data
which he collected.
(3) The inferences from his experiments on successive generations of
test plants showed that his results are in accordance to general rules
of inheritance rather than being unsubstantiated ideas.
Mendel's Experimental Background
Mendel selected garden pea – Pisum sativum for his experiments. The
reasons for adopting this plant were:
(1) Pea plants are annual plants with shorter life span.
(2) Flowers demonstrate self-pollination as the plant has bisexual
cleistogamous flowers (closed flowers), but cross-pollination is also
possible.
(3) Pea plant is easily available on a large scale.
(4) Pea plants can be easily grown and maintained.
(5) Pea plant has many distinct contrasting characteristics. The plants
show clearly distinct two opposing traits, e.g., tall or dwarf plants,
yellow or green seeds, etc.
Fourteen true-breeding pea plant varieties were selected by Mendel, as
pairs which were similar except for one character with contrasting traits.
The seven contrasting characteristics of garden pea plant studied by
Mendel were:
Principles of Inheritance and Variation 3
Click here to access complete Educart book of Biology (Special Discount)
