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GENETICS/2021 SOHSS AREEKODE
the stable trait inheritance and expression for
PRINCIPLES OF INHERITENCE AND VARIATION several generation.
Genotype
The complete genetic constitution of an
Genetics
organism is called Genotype.
It deals with the inheritance, as well as the
Eg: Tt,TT,RR,Rr,YY,Yy
Variation of characters from parents to
offspring.
Homozygous (True breeding/Pure line)
It is the study of genes and chromosomes
An organism with 2 identical allele of a gene
Inheritance
Eg:TT,RR,YY,YY,rr,tt
Inheritance is the process by which characters
are passed on from parent to progeny. it is the
Heterozygous
basis of heredity
An organism with 2 different allele of a gene
Ie: Heredity is the tendency of offspring to
Eg:Tt,Rr,Yy
resemble their parents
Variation
Character and Trait
It is the tendency of offspring to differ from their
A character is a heritable feature that varies
parents
among individuals.
The main reason for variations are
Eg: Flower color,Plant Height,seed shape, Eye
Crossing over
colour.
Mutation
A trait is a variant for character,
Human knew from as early as 8000-1000BC that
Eg: white or purple colors for flowers, Dwarf
one of the cause of variation was hidden in
plant, Round seed, Blue eye.
sexual reproduction .They exploited variation
seen in nature (Plants and animal) to select
Qn. An elephant always gives birth to a baby
organism with desirable characters. However,
elephant and not some other animal, why ?
early humans had very little idea about the
Ans:
scientific basis of variation.
Eg: Sahiwal cow (Punjab) (through artificial selection Qn. A mango seed forms only a mango plant and not
and domestication from ancestral wild cows)
any Other plant why ?
Ans:
GENETIC TERMS
Allele :
They are alternative form of a gene / Genes
which code for a pair of contrasting traits are GREGOR JOHANN MENDEL
known as alleles. He was an Austrian monk.
Eg: T,t,R,r,Y,y
He is known as father of genetics.
He conducted hybridisation experiment on
Phenotype
The physical appearance of an organism is garden pea plant (Pisum sativum ) for 7 years
called Phenotype (1856-1863)
The visible/oservale characterstics of an Based on his experiment , he proposed ‘laws
organism is called phenotype of inheritance’ in living organisms .
Eg: Tall plant, blue eye, round seed During Mendel’s investigations into
inheritance patterns , it was for the first time
True breeding line that statistical analysis and mathematical
A true breeding line is one that, having logic were applied to problems in biology
undergone continuous self-pollination, shows
Principles of inheritance and variation/2021 video lesson
, Join Telegram Channel: https://t.me/hsslive Downloaded from www.Hsslive.in ®
GENETICS/2021 SOHSS AREEKODE
Mendel selected 14 true-breeding pea plant Monohybrid cross-
varieties, as pairs which were similar except for
Inheritance of one gene
one character with contrasting traits.
It is the cross involving two forms of a
The garden pea plant contains number of
single character.
characters. Out of these, he selected and studied
only 7 characters. Each of these 7 characters has 2
It is the simplest cross performed by Mendel
verities. The 7 characters are given below. Mendel crossed tall plants and dwarf pea
plant to study the inheritance of one gene.
Sl Character Contrasting traits He collected seed produced as a result of
No. Dominant Recessive above cross and grew them to generate F1
1 Height of the plants Tall Dwarf (Filial 1 Progeny ).
2 Seed shape Round Wrinkled Mendel observed that all the F1 progenies
3 Seed colour Yellow Green
were tall (Like one of its parent and none
4 Pod shape Inflated Constricted
(full) were dwarf )
5 Pod colour Green Yellow
6 Flower position Axial Terminal He made similar observations for the other
7 Flower color Violet White pairs of traits – he found that the F1 always
resembled either one of the parents, and
that the trait of the other parent was not
seen in them.
He then self pollinated the F1 progeny (Tall
plants ) to generate F2. He observed that
75% of the F2 progenies were tall and
25% were dwarf (Ie: 3:1)
Ie: characters that was not seen in the F1
generation expressed in the F2 (dwarf)
He also found that ,The tall and dwarf traits
were identical to their parental type and
did not show any blending, that is all the
offspring were either tall or dwarf, none
were of in between height No blending of
characters in offsprings.
Based on this observation Mendel proposed
that something being was being stably
passed down unchanged from parents to
Reason for selecting garden pea plant offspring through gametes over successive
1. It has short life cycle so it gives quick results. generation. Mendel called it as factors. Now
2. Plants shows clear contrasting character we called them as genes.
3. Being a herb, it is Easy to cultivate
Genes, therefore, are the units of
4. It has bisexual flower
inheritance. They contain the
5. It is generally self pollinated and so self
information that is required to express a
fertilised. However , it can e Cross
pollination is easy if self pollination is particular trait in an organism. Genes is a
prevented. chemically a segment of DNA (RNA in some
virus )
Principles of inheritance and variation/2021 video lesson
, Join Telegram Channel: https://t.me/hsslive Downloaded from www.Hsslive.in ®
GENETICS/2021 SOHSS AREEKODE
Example-1
Monohybrid genotypic ratio= 1:2:1
Monohybrid phenotypic ratio =3:1
Monohybrid genotypic ratio= 1:2:1
Monohybrid phenotypic ratio =3:1
Similar results were obtained with the
other traits that he studied (Seed
shape,flower colour etc.): only one of the
parental traits was expressed in the F1
generation while at the F2 stage both the
traits were expressed in the proportion
3:1. The contrasting traits did not show
any blending at either F1 or F2 stage
Example-2
PUNNET SQUARE
It was developed by British geneticist
Reginald C Punnet
It is the graphical representation to
calculate the probability of all possible
genotype of an offspring in a genetic
cross .
The possible gametes are written on 2
sides, usually on the top row and left
column. All possible combinations are
written in boxes below in square.
Principles of inheritance and variation/2021 video lesson
GENETICS/2021 SOHSS AREEKODE
the stable trait inheritance and expression for
PRINCIPLES OF INHERITENCE AND VARIATION several generation.
Genotype
The complete genetic constitution of an
Genetics
organism is called Genotype.
It deals with the inheritance, as well as the
Eg: Tt,TT,RR,Rr,YY,Yy
Variation of characters from parents to
offspring.
Homozygous (True breeding/Pure line)
It is the study of genes and chromosomes
An organism with 2 identical allele of a gene
Inheritance
Eg:TT,RR,YY,YY,rr,tt
Inheritance is the process by which characters
are passed on from parent to progeny. it is the
Heterozygous
basis of heredity
An organism with 2 different allele of a gene
Ie: Heredity is the tendency of offspring to
Eg:Tt,Rr,Yy
resemble their parents
Variation
Character and Trait
It is the tendency of offspring to differ from their
A character is a heritable feature that varies
parents
among individuals.
The main reason for variations are
Eg: Flower color,Plant Height,seed shape, Eye
Crossing over
colour.
Mutation
A trait is a variant for character,
Human knew from as early as 8000-1000BC that
Eg: white or purple colors for flowers, Dwarf
one of the cause of variation was hidden in
plant, Round seed, Blue eye.
sexual reproduction .They exploited variation
seen in nature (Plants and animal) to select
Qn. An elephant always gives birth to a baby
organism with desirable characters. However,
elephant and not some other animal, why ?
early humans had very little idea about the
Ans:
scientific basis of variation.
Eg: Sahiwal cow (Punjab) (through artificial selection Qn. A mango seed forms only a mango plant and not
and domestication from ancestral wild cows)
any Other plant why ?
Ans:
GENETIC TERMS
Allele :
They are alternative form of a gene / Genes
which code for a pair of contrasting traits are GREGOR JOHANN MENDEL
known as alleles. He was an Austrian monk.
Eg: T,t,R,r,Y,y
He is known as father of genetics.
He conducted hybridisation experiment on
Phenotype
The physical appearance of an organism is garden pea plant (Pisum sativum ) for 7 years
called Phenotype (1856-1863)
The visible/oservale characterstics of an Based on his experiment , he proposed ‘laws
organism is called phenotype of inheritance’ in living organisms .
Eg: Tall plant, blue eye, round seed During Mendel’s investigations into
inheritance patterns , it was for the first time
True breeding line that statistical analysis and mathematical
A true breeding line is one that, having logic were applied to problems in biology
undergone continuous self-pollination, shows
Principles of inheritance and variation/2021 video lesson
, Join Telegram Channel: https://t.me/hsslive Downloaded from www.Hsslive.in ®
GENETICS/2021 SOHSS AREEKODE
Mendel selected 14 true-breeding pea plant Monohybrid cross-
varieties, as pairs which were similar except for
Inheritance of one gene
one character with contrasting traits.
It is the cross involving two forms of a
The garden pea plant contains number of
single character.
characters. Out of these, he selected and studied
only 7 characters. Each of these 7 characters has 2
It is the simplest cross performed by Mendel
verities. The 7 characters are given below. Mendel crossed tall plants and dwarf pea
plant to study the inheritance of one gene.
Sl Character Contrasting traits He collected seed produced as a result of
No. Dominant Recessive above cross and grew them to generate F1
1 Height of the plants Tall Dwarf (Filial 1 Progeny ).
2 Seed shape Round Wrinkled Mendel observed that all the F1 progenies
3 Seed colour Yellow Green
were tall (Like one of its parent and none
4 Pod shape Inflated Constricted
(full) were dwarf )
5 Pod colour Green Yellow
6 Flower position Axial Terminal He made similar observations for the other
7 Flower color Violet White pairs of traits – he found that the F1 always
resembled either one of the parents, and
that the trait of the other parent was not
seen in them.
He then self pollinated the F1 progeny (Tall
plants ) to generate F2. He observed that
75% of the F2 progenies were tall and
25% were dwarf (Ie: 3:1)
Ie: characters that was not seen in the F1
generation expressed in the F2 (dwarf)
He also found that ,The tall and dwarf traits
were identical to their parental type and
did not show any blending, that is all the
offspring were either tall or dwarf, none
were of in between height No blending of
characters in offsprings.
Based on this observation Mendel proposed
that something being was being stably
passed down unchanged from parents to
Reason for selecting garden pea plant offspring through gametes over successive
1. It has short life cycle so it gives quick results. generation. Mendel called it as factors. Now
2. Plants shows clear contrasting character we called them as genes.
3. Being a herb, it is Easy to cultivate
Genes, therefore, are the units of
4. It has bisexual flower
inheritance. They contain the
5. It is generally self pollinated and so self
information that is required to express a
fertilised. However , it can e Cross
pollination is easy if self pollination is particular trait in an organism. Genes is a
prevented. chemically a segment of DNA (RNA in some
virus )
Principles of inheritance and variation/2021 video lesson
, Join Telegram Channel: https://t.me/hsslive Downloaded from www.Hsslive.in ®
GENETICS/2021 SOHSS AREEKODE
Example-1
Monohybrid genotypic ratio= 1:2:1
Monohybrid phenotypic ratio =3:1
Monohybrid genotypic ratio= 1:2:1
Monohybrid phenotypic ratio =3:1
Similar results were obtained with the
other traits that he studied (Seed
shape,flower colour etc.): only one of the
parental traits was expressed in the F1
generation while at the F2 stage both the
traits were expressed in the proportion
3:1. The contrasting traits did not show
any blending at either F1 or F2 stage
Example-2
PUNNET SQUARE
It was developed by British geneticist
Reginald C Punnet
It is the graphical representation to
calculate the probability of all possible
genotype of an offspring in a genetic
cross .
The possible gametes are written on 2
sides, usually on the top row and left
column. All possible combinations are
written in boxes below in square.
Principles of inheritance and variation/2021 video lesson
