Download 94 Didn`t you notice the conversation between the grandmother and

BIOLOGY
Though she
herself broods
her eggs how
different her
offsprings are!
Grandma!
Whom do I
look like?
Didn't you notice the conversation
between the grandmother and the child
and the thoughts of the zebra and the hen?
Are the lines on all zebras alike? Aren't
there resemblances between the hen and
the chickens? How is it that the grandchild
has features of the grandmother besides
those of her father and mother? Don't you
find such examples in your surroundings?
The similarities between parents and
children are due to the transmission of
characters from parents to offsprings. But
are the characters of parents alone
transmitted to offsprings? Note down
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Who drew
the lines on
their bodies so
exactly!
Father’s colour-Mother’s hair --Then --------------eyes, your
Grandma's
your opinion.
...................................................................
Why is it that only some of the characters
of parents are expressed in offsprings?
How is it that differences also occur along
with similarities? Such questions and the
assumptions related to them have arisen
since very ancient times. But an effort to
find a scientific explanation to these was
initiated by Gregor Johann Mendel. Hence
he is known as the Father of Genetics.
Collect more information on Mendel's
contributions based on the description
given below.
BIOLOGY
Gregor Mendel - The Father of Genetics
Gregor Johann Mendel was born in a middle class peasant family at Brunn in Austria
(now Czech republic) in 1822. After school education, he studied theology and became
a priest. He also worked as a teacher after studying Physical Science
and Natural Science at the Vienna University. The experiments
conducted in pea plants while being a priest and the inferences he
arrived at, elevated him to the status of the Father of Genetics.
Mendel analysed the inheritance of 7 pairs of contrasting characters
in pea plants in detail. The colour of the flower (red, white), seed
colour (yellow, green), shape of the seed (round, wrinkled), height of
Gregor Johann
the stem (tall, short) etc. were some of the contrasting characters
Mendel
subjected to hybridisation experiments. From his experiments he
arrived at certain inferences.
—
A pair of factors responsible for each character is present in all organisms. He
indicated these factors by using symbols.
E.g.
Tallness
Dwarfness
- TT
- tt
Red flower
White flower
- RR
- rr
—
One factor in each pair is received from the mother and the other from the father.
—
There will not be any change in the result of the experiment whether contrasting
characters are from the female parent or the male parent.
—
Factors of both the contrasting characters (qualities) will be present in plants of F 1
generation, but only one character will be expressed.
Even though Mendel's findings were published in 1866, it didn't get enough recognition.
Mendel died in 1884. Sixteen years after his death, scientists like Hugo de Vries, Carl
Correns and Erich Tschermak independently discovered Mendel's laws of inheritance
and reformulated them. With that Gregor Johann Mendel was accepted as the Founder
of Heriditary Science. Genetics, the branch of science which deals with heredity and
variations was formed only after that.
From his experiments in pea plants,
Mendel formulated certain laws. These
are known as Mendel's laws of
inheritance. Examine Illustrations 7.1, 7.2,
7.3 and 7.4. Fill them up suitably and
analyse on the basis of indicators. Prepare
notes on the basis of your understanding
of the relationship between the results of
the experiments and Mendel's laws.
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BIOLOGY
Experiment - 1
Cross Pollination between Tall and Dwarf Pea Plants
Female parent (Tall)
male parent (dwarf)
TT
tt
Gametes
T
t
(.........................................)
Tt
First filial generation (F1 generation)
Illustration 7.1
Indicators
—
Which is the character expressed in F1
generation?
—
Which is the character not expressed?
—
What is the difference between the
factors contained in the Tall female
parent and the offsprings of F 1
generation?
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Law of Dominance
When a pair of contrasting characters
combines, only one is expressed
(dominant character) and the other
remains hidden (recessive character).
BIOLOGY
Experiment - 2
Self Pollination of F 1 generation
F1 generation
(.........................................)
Tt
Female gametes
Male gametes
t
T
..........
......................................... .........................................
TT
..........
.........................................
.........................................
..................
..................
Tt
Second filial generation (F2 generation)
Illustration 7.2
Indicators
—
What are the differences observed in the
progenies of the second generation from
the first generation?
—
What is the ratio in which tall and dwarf
plants are formed in the second
generation?
—
Is the genetic constitution of all tall
plants of the second generation the same?
—
How do the factors seen as pairs in the
female parent (Tt) appear in the
gametes?
Law of Segregation
During gametogenesis, the pair of
hereditary factors that determine the
characters segregate from each other,
and only one factor enters each gamete.
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BIOLOGY
Experiment - 3
If more than one character combines?
male parent
(dwarf with white flowers)
Female parent
(tall with red flowers)
TTRR
ttrr
TR
tr
Gametes
F1 generation
(........................................................)
TtRr
Illustration 7.3
Indicators
—
Which are the dominant characters
here?
—
Which are the recessive characters?
What is the difference between the
factors in the offsprings of F1 generation
and factors in the parental plants?
—
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Illustration 7.4. shows the experiment
conducted by Mendel subjecting the F1
generation of Experiment 3 to selfpollination. Observe the Illustration and
fill up Table 7.1. Prepare notes based on
the indicators.
...................................................................
BIOLOGY
Experiment - 4
Self Pollination of F 1 Generation
F1 generation
—
Which are the new types among the
progeny?
—
Are the characters which remained
together in the parental plants of the
F1 generation transmitted together to
all offsprings? If not how? Note down
your inference.
...................................................................
Compare your inference with the Law of
Independent Assortment.
(......................................)
Tt Rr
Law of Independent Assortment
Female gametes
Male gametes
TR ........ ........ ........
........ ........ ........ ........
Illustration 7.4
Let us see what happens when these
gametes fuse?
Male Gametes
Female gametes
TR
TTRR
TR
Tr
tR
TTRr
TtRR
tr
TtRr
Tr
............... ............... ............... ...............
tR
............... ............... ............... ...............
tr
............... ............... ...............
ttrr
Tall with red flowers
: …………….
Dwarf with red flowers
: …………….
Tall with white flowers
: …………….
Dwarf with white flowers : …………….
Ratio of F2 progeny : ………........................
Table 7.1
Indicators
—
How many types of gametes are
formed? Which are they?
—
How many types of progenies are
formed? Which are they?
When two or more pairs of characters
combine, factors for each character pair
segregate and assort independently to
pass on to the next generation.
Though characters in parents are not
expressed in children, sometimes they
get expressed in their grand children.
What is the reason for this? Discuss and
prepare notes based on Mendel's Law of
Inheritance.
...................................................................
Mendel tried to prove that characters are
inherited from parents to offsprings
through certain factors. What are these
factors? Where are they situated? A lot of
research has been done in these directions
after Mendel. Many new findings resulted
from this. These findings later grew into
the extensive branch of science called
Genetics. Some important milestones in
the history of Genetics are given below.
Analyzing them and collecting more
information, prepare notes on the
development of Genetics.
...................................................................
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BIOLOGY
Milestones in the History of Genetics
Johannsen : Coined
Gregor Johann Mendel
1866 Formulated the Laws
1909 the term gene to the
heriditary factors
explained by Mendel.
of Inheritance.
Friedrich Meischer
1869 Discovered Nucleic acid
Johannsen
Friedrich Meischer
Hugo de Vries, Erich Tschermak,
O. Avery : Research
under his
leadership identified
DNA as the genetic
material
1900 Carl Correns: Reformulated Mendel's 1943 team
Laws.
Avery
1953
Hugo de Vries
Erich Tschermak
Carl Correns
James
Watson,
Francis
Crick:
Presented the spiral helix model of
DNA
Walter S.Sutton, Theodor Boveri
1902 Discovered that hereditary factors are
located in chromosomes.
James Watson & Francis Crick
1970
Walter S.Sutton
William
Marshall Nirenberg, Har Gobind
Khorana Discovered the Genetic
Code
Theodor Boveri
Bateson
1905 Named the new branch
of science which deals
with the study of
heredity and variation
as Genetics.
William Bateson
Marshall Nirenberg
Har Gobind Khorana
Mendel's hypothesis that inheritance of characters is through certain factors was later
proved correct. It was made clear that every character in an organism is controlled by
genes which are parts of DNA (deoxyribonucleic acid) molecules. The DNA molecule
is formed by two strands of nucleotides. The DNA molecule has the shape of a spiral
double helix with two longitudinal strands made up of sugar and phosphate and steps
made up of nitrogen bases. This structure was presented by Watson and Crick. Analyse
Illustration 7.5. based on the indicators and prepare a note on the DNA molecule.
..............................................................................................................................
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BIOLOGY
Indicators
Cell
Chromosome
—
Where is the DNA chiefly found?
—
What are nucleotides? What are its
components?
—
Which are the nitrogen bases that pair
with each other?
Nucleus
DNA ultra structure
DNA
Specific parts of the DNA are responsible
for regulating metabolism and effecting
specific characters. These parts are known
as genes. How do genes perform their
functions? Examine the given description
and Illustration 7.6. and prepare a note.
...................................................................
Gene Action
Nucleotide
Phosphate
Nitrogen base
Deoxyribose Sugar
Nitrogen bases - 4 types
Adenine-A
Thymine - T
Cytosine-C
Guanine-G
Nucleotides in DNA
Formation of specific characters and
regulation of metabolism are done by
proteins. Genes in the DNA determine
which types of proteins are to be made.
DNA does not manufacture protein
directly. DNA makes RNA (Ribonucleic
acid) from its own strands. RNA reaches
ribosomes and synthesizes proteins by
linking together of amino acids.
Information for the synthesis of specific
proteins is encoded in each gene.
Nuclear membrane
DNA
Different amino acids Protein
Molecule
RNA
Adenine nucleotide
Cytosine nucleotide
DNA unwinds and
RNA is synthesized
Ribosome
Thymine nucleotide
Guanine nucleotide
Deoxyribose sugar
Illustration - 7.5
Illustration - 7.6
Protein synthesis
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BIOLOGY
Indicators
—
Where is RNA synthesized?
—
Where does this RNA reach?
—
What is the role of RNA in protein
synthesis?
Haven't you understood that DNA
performs its function by synthesizing
another nucleic acid called RNA?
Observing the differences between RNA
and DNA given in Illustration 7.7 fill up
the Table 7.2 given below.
Strands made up of
sugar and phosphate
molecule
of DNA. Proteins responsible for specific
characters are synthesized according to the
directions of hereditary factors called
genes. Offsprings get these genes from
parents. If it is so, should'nt the offspring
get characters only from parents? Some
times characters different from parents are
expressed in offsprings. These are called
variations. How do variations occur?
Haven't you studied that gametes are
formed by meiosis? Homologous
chromosomes from the mother and father,
pair and exchange chromosomal material
during meiosis. Analyse Figure 7.1. and
form inferences.
Crossing over in Meiosis Different stages
Nitrogen bases
DNA
Chromosome pair
RNA
Nucleotides in RNA
Chromosome from
mother
Chromosome from
father
Adenine
Cytosine
Beginning of crossing over
Uracil
Guanine
Ribose sugar
Phosphate
The chromosome pairs exchanging genes
Illustration 7.7
Characteristics
DNA
RNA
Number of strands
Type of sugar
Daughter chromosomes after the exchange of genes
Nitrogen base
Table 7.2
You have understood that specific proteins
are responsible for all the processes taking
place in the cells and proteins are
synthesized according to the instructions
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Fig.7.1. Gene exchange (different stages of exchange of
genetic material by chromosome pairs during meiosis).
BIOLOGY
Haven't you understood that exchange of
genes causes variations in offsprings?
Variations are seen in offsprings because
characters that are hidden in parents also
get transmitted to offsprings.
Now we have understood the role of
chromosomes and the genes in the
development of characteristics of an
organism. But due to several reasons there
may be changes in chromosome number
and structure. Such spontaneous changes
are called mutations. These are inherited.
Most of the mutations are harmful to
organisms. Pictures and the press report
given below include some such examples.
Find more examples.
Sickle cell anaemia widespread
among tribals
Thiruvananthapuram: Study reports
reveal that the genetic disease called sickle
cell anaemia is widespread among tribals.
Decrease in the oxygen carrying capacity
of the red blood cells as it bends like a sickle
is the notable feature of this disease. In the
gene structure..
Child - male or female?
What is the reason behind the formation
of a male or female child?
Analyse Illustration 7.8. based on
indicators and form inferences.
...................................................................
Mother
Turner syndrome
Loss of one sex
chromosome (only
one X chromosome,
no Y chromosome).
Deficient females
Turner syndrome
Chromosomes = 44 + X with sterility and
dwarfness.
Autosomes = 44
Sex chromosomes
= xx
Total = 46
XX
Female gametes
Father
XY
Autosomes = 44
Sex chromosomes
= xy
Total = 46
Male gametes
Down syndrome
One extra autosomal
chromosome (three
chromosomes in 21st
pair, total 47
Chromosomes). Mental
retardation, sterility, low
immunity.
Down syndrome
Chromosome = 45 + XX or 45 + XY
Female
Child
XX
................
................
................
Illustration - 7.8
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BIOLOGY
Indicators
—
How many types of sex chromosomes
are there?
—
What are the similarities and
dissimilarities
between
the
chromosomes of man and woman?
—
What is the probability of formation of
male and female children?
Haven't you understood that sex
chromosomes in males play a major role
in sex determination? This is the reason
for the more or less equal proportion of
female- male ratio.
How difficult it is to assess the
contributions of genetics to human
progress! Like any other branch of science,
is there a possibility to make genetics also
a means of exploitation? Read the article
given below, collect additional
information and conduct a debate on the
topic.
The Branch of Science that Transforms the Living World
The genetic revolution that was started by Gregor Mendel in pea plants has developed
to such an extent that today it influences all sections of society. The knowledge we have
gained about genes and the technology that alters genetic structure are progressing
every moment. Technology that is used to make desired changes in genetic structure is
called genetic engineering or recombinant DNA technology. Right at the outset of the
1970s, the scientific world gained the ability to cut the DNA at specific sites. Enzymes
which are used to cut DNA at specific sites are called molecular scissors. Restriction
endonuclease enzymes belong to this category. Similarly, enzymes like ligase bind genes.
Such enzymes are called molecular glues.
Genetic engineering has caused tremendous changes in the field of agriculture and
medicine. Insulin, for the treatment of diabetes was extracted from animals. This caused
allergy - like problems. But today insulin without any side effects is being manufactured
through genetic engineering. The insulin gene separated from human beings is combined
with bacterial DNA and using this bacteria, human insulin is manufactured.
Bt cotton and Bt Brinjal which triggered so many hot discussions in the field of agriculture
are the products of genetic engineering (Bt-Bacillus
thuringiensis). The gene when introduced in these plants cause
the production of a protein. Since this protein can destroy pests,
pest control is possible without pesticides. However studies are
yet to be completed to ensure whether
it has any side effects in human beings.
Bt Cotton
Bt Brinjal
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Another product of genetic engineering
is super bugs. These are new types of
bacteria produced by combining
different types of bacterial genes.
Some super bugs eat and destroy
petroleum products. This bacterium
can be used as a remedy for oil spills
BIOLOGY
in oceans and for the clearing of obstructions in oil pipes. This super bug was first
produced by Anand Mohan Chakrabarty of Indian origin.
Many improved agricultural crop varieties could be produced through artificially created
mutations. The DNA finger printing which is used to prove disputed parentage and criminal
offenses, is a contribution of genetics.
By 2003 we attained complete knowledge about the nucleic acid
sequence in human chromosomes through the Human Genome
Project. This is considered as a major achievement which could
result in a major leap in therapeutics. Geneticists all over the world
are still at work in their laboratories for many more achievements.
But one cannot ignore situations where such achievements may
be used for exploitation and selfish motives. What will be the
future of the human race, if pathogens, which will not yield to any
medicine, are used as biological weapons? What will happen if
Dr. Anand Mohan
super bugs, that can be used to prevent oil pollution, are introduced
Chakrabarty
in oil fields? Science always has the potential to be the protector
of man. But some times, man misuses science for destructive
purposes. While being proud of the boons of science we should be able to use it for the
benefit of the human race too.
Science is a product of collective human thought. Only when it is used for the benefit
of mankind, we can do justice to our ability to think. The individual and the society
should be able to approach science with such an attitude.
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BIOLOGY
Follow up Activities
1. The offsprings of two types of hybridization of homozygous black and white rabbits
are illustrated.
White female rabbit
Black male rabbit
C
Black female rabbit
White male rabbit
D
a. Is the coat colour sex-linked?
b. When C and D are crossed, what will be the colour of the coat in the offsprings?
2. A husband, along with other family members, constantly accused his wife of
delivering only female children. As a science student what is your response to this
attitude. State with definite reasons.
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