SEE Science (Heredity) Notes
Heredity
1. Why Mendel is called the father of
genetics? Why?
Ans: Gregor Johann Mendel
(1822-1884 AD), is considered as the father of genetics because he introduced
the concept of genes as the basic unit of heredity for the first time.
2. What are 'dominant characteristics'? Give one example.
Ans: The characteristics which
are prominent and appear in successive generations by covering other characters
are called dominant characteristics.
For example: In the
cross-pollination between tall pea plant and dwarf pea plant, tall is dominant
characteristics.
Recessive characters:
Those characters in a cross which are unable to express themselves in successive
generation due to the presence of dominant characters are called recessive
characters.
For example: In the cross-pollination
between tall pea plant and dwarf pea plant, dwarf is dominant characteristics.
3. What are hybrids? How are they produced? State their types.
Ans: Hybrids are the organisms
produced after cross-fertilization between two genetically different organisms.
In other words, hybrids are those organisms which have phenotype and genotype
different. For e.g. When a pure tall plant is crossed with pure dwarf plant
then hybrid tall plant is produced.
When cross is made between two pair of pure contrasting characteristic
then hybrid is produced. Hybrids are the various types e.g. Monohybrids, Dihybrids
etc.
4. Differentiate between:
a) Monohybrid
cross and Dihybrid cross
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Monohybrid cross
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Dihybrid cross
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1. The cross involving
only one pair of contrasting characteristics is called monohybrid cross
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1. The cross involving
two pairs of contrasting characteristics is called dihybrid cross.
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2. As a results of
monohybrid cross, offspring having phenotypic ratio of 3:1 are produced in F2
generation. e.g. cross between a tall pea plant with a dwarf pea plant
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2. As a result of
dihybrid cross, offspring having phenotypic ratio of 9:3:3:1 are produced in
F2 generation. e.g. cross between red flowered tall pea plant with
white flowered dwarf pea plant.
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b) Phenotype and genotype
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Phenotype
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Genotype
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1. The external
appearance of an organism for a contrasting character is called phenotype.
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1. The genetic make-up or
genetic constitution of an organism is called genotype.
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2.
It is expressed in words, e.g. tall, dwarf, etc.
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2. It is expressed in
letters, e.g. TT (pure tall plant), Tt (Hybrid tall plant, tt (pure dwarf
plant), etc.
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3. Parental
characteristics of an organism cannot be found from phenotype of an organism
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3. Parental
characteristics of an organism can be found from the genotype of an organism.
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5. Why did Mendel select peas plants for his study? Give any four
reasons.
Ans: Mendel selected pea plants
(i.e. Pisum sativum) for his study because of the following reasons:
i) Pea plants contain a
large number of contrasting characteristics in pairs such as tall (T) and dwarf
(t), round (R) and wrinkled (r) sees, smooth (I) and constricted (i) pea pods,
etc.
ii) They have short life cycle.
iii) They can be cultivated easily.
iv) They produce a large
number of offspring after each successive mating.
v) They are
easy to handle.
6. State Mendel's 'Law of Dominance'.
Ans: According to Mendel's
experiments, 'Law a Dominance' states that, "When a cross is made between a
pair of pure contrasting characteristics, only one of them is able to express
itself phenotypically while other remains hidden in F1 generation."
7. State Mendel's second law (i.e. law of segregation or law of
purity of gametes).
Ans: Mendel's second law i.e. law
of segregation states that, "The hybrid offspring obtained in F1
generation contain two contrasting characteristics of dominant and recessive
nature. These characteristic remain together for a long period of time in the
hybrids but not mix with each other and separate or segregate at the time of
gamete formation so that each gamete gets only one characteristic, either
dominant characteristic or recessive characteristic."
8. State Mendel's 'Law of
independent assortment'.
Ans: The "law of
independent assortment" states that "When two pairs of independent
alleles are brought in the hybrid (F1), they at the time of gamete
formation, segregate or assort at random and freely."
9. Define mutation with
examples.
Ans: A suddenly chromosomal
change by which variation occurs in organisms is called discontinuous variation
or mutation. For example, a newly born baby without leg, with extra finger on
hand, etc.
10. Does Mendel's law
applies to human beings too? State any two difficulties Mendel would have faced
if he had carried his experiment on
human beings instead of pea plants.
Ans: Yes, Mendel's law applies to
human beings too. But while performing this experiment on human beings, many
problems would rise. If he had carried out his experiment on human beings
instead of pea plants, he would have faced following difficulties:
i) In practical life, it would be difficult for him to
cross between selected men and women for any two contrasting characteristics. They might not accept for crossing due to the
social norms.
ii) In human there is absence of large number of pair of
contrasting characteristics.
iii) Life span of human being is too long.
11. A tall (T) pea plant
and a dwarf (t) pea plant were first cross-pollinated and then self-pollinated.
The given table shows the result of
this experiment. Answer the following questions with the help of this table.
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T
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t
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T
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TT
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Tt
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t
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Tt
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tt
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i) Which filial generation
does this result belong to?
Ans: This result belongs to second filial (F2)
generation.
ii) What is the percentage of pea
plants having hybrid character?
Ans: The
percentage of pea plants having hybrid character is 50.
iii) What pair of genes indicates pure tall plant?
Ans: The 'TT' pair of genes
indicates pure tall plant.
12. Yellow coloured round seeded pea
plants and green coloured wrinkle seeded pea plants are first cross-pollinated
and then self-pollinated. The result hence obtained is shown in the following
table. Answer the following questions on the basis of this table.
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YR
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Yr
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yR
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yr
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YR
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YYRR
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YYRr
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YyRr
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YyRr
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Yr
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YYRr
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YYrr
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YyRr
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Yyrr
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yR
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YyRR
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YyRr
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yyRR
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YyRr
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Yr
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YyRr
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Yyrr
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yyRr
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yyrr
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R =
round (dominant) r = wrinkled (recessive) Y = yellow (dominant)
y = green (recessive)
i) Which filial generation does this result
belong to?
Ans: This result belongs to second
filial (F2) generation.
ii) Write the phenotypic ratio (Round yellow
seeds: round green seeds: wrinkled yellow seeded) of this result.
Ans: The phenotypic ratio of round
yellow seeds: round green seeded: wrinkled yellow seeded: wrinkled green seeded
pea plant is 9:3:3:1 respectively.
iii) Which types of peer generation of seeded
pea plant are indicated by YyRr and YYrr?
Ans: YyRr and YYrr indicate hybrid
pea plant with round yellow seeds and wrinkled yellow seed respectively.
13. What is meant by genetic variation?
Ans: Genetic variation is defined as the differences
among the members of a species.
14. After the mating of a black dog
with a brown dog, all the offspring in the F1 generation were black. Why brown
dog is not seen in
the offspring?
Ans: According to Mendel's law of
dominance, in crossing between pure organisms for contrasting characteristics
of a pair, only one character of the pair appears in the first generation. The
dominant character suppresses the recessive character in F1 - generation.
When a black dog and a brown dog are crossed, all dogs become black as the
black character. Suppresses the brown character in F1 - generation.
15. For mice, black (B) is a dominant phenotype
and white (b) is recessive. In a certain experiment, a black male mouse of
genotype Bb is crossed with a white female
of genotype bb. Show with the help of a chart diagram that, when babies are
produced, the ratio
of black babies and white babies will be 1:1.
Ans: the chart diagram for
crossing between a black male mouse of genotype (Bb) and a white female mouse
of genotype (bb) is shown below:
16. Explain the region that only one
characteristic is found expressed in F1 generation of Mendel's
experiment. The characteristic which is not seen in F1 generation is
found expressed in F2 generation after crossing the hybrid of F1 generation, how?
Ans: In F1 -
generation, both characteristics of dominant and recessive nature remain
together for a long time but do not mix with each other in hybrids and finally
separate into two different pure gametes. Those hybrids after interbreeding
produce different types of offspring in F2 - generation. Due to the
segregation of gametes, the characteristic which is not seen in F1 -
generation is found expressed in F2 - generation.
17. Every living being reproduces its own kind of
offspring, why?
Ans: Genes are responsible for
transmitting hereditary characteristics from parents to their offspring.
Therefore, every living being reproduces its own kinds.
18. What are indicated by ATGC?
Ans: The nitrogen bases present in
the DNA are indicated by ATGC in which
A – Adenine
T - Thymine
G – Guanine
C – Cytosine
19.
DNA (Deoxyribose Nucleic Acid):
DNA is double stranded helically coiled macromolecule which is commonly found
in chromosome.
20.
RNA (Ribose Nucleic Acid):
RNA is a single stranded macromolecule which is commonly found in cytoplasm and
nucleus of a cell.
21. The nitrogen bases present
in the RNA are indicated by AGUC in which
A – Adenine
T - Thymine
U – Uracil
C – Cytosine
22. Variation: The structural differences
that provide individuality to each member of a species is called variation.
23. Heredity: The process, by which
living organism transmits parental characteristics to their offspring, is
called heredity or inheritance.
25. Differences between.
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DNA
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RNA
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It
is Deoxyribose Nucleic Acid.
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It
is Ribose Nucleic Acid.
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It
is double stranded.
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It
is single stranded.
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It
transfers the parental characters into offspring.
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It
synthesizes protein.
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It
contains deoxyribose sugar.
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It
contains ribose sugar.
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26. Name the sugar present in
RNA.
Ans: The sugar present in RNA is
ribose sugar.
27. Write the name of
sex-linked disease only seen in male and female.
Ans: Sex-linked disease only
seen in male are:
a) Colour blindness
b) Haemophilia
c) Baldness
Sex-linked
disease only seen in female are:
a) Breast cancer
b) Uterine cancer
28. Differences
between
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Dominant
character
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Recessive
character
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It
appears in successive generation.
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It
remains hidden in successive generation.
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It
suppresses the recessive characteristic.
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It
is suppressed by dominant characteristic.
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Tall
is dominant over dwarf in pea plant.
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Dwarf
is recessive over tall in pea plant.
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