Science Project Work 2013
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Transcript of Science Project Work 2013
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SUBMITTED TO: - SUBMITTED BY:-
ARCHANA MALHOTRA NISHA RAI
X-D
ROLL NO 42
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Introduction
A Recognizable feature of a human being like height, complexion, shape of hair,
color of eyes and shape of nose and chin, etc, are called CHARACTER or
TRAITS.
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The transmission of characters from the parents to their offsprings is called
HEREDITY. In most simple words, Heredity means continuity of features from
one generation to the next.
Actually the Hereditary information is present in the sex cells of the parents.Thus, gametes constitute the link between one generation and the next, and pass
on the parental (fathers) and maternal (mothers) characters or traits to the
offspring.
The inheritable characteristics may be morphological/anatomical/physiological/
reproductive and are also known as traits. If we take a very close look at the
rules of inheritance, both father and mother contribute equal amount of genetic
material to the child. This means that each trait can be influenced by both
paternal and maternal genetic materiali.e., DNA.
Gregor Johann Mendel(1822-1884) worked out the first ever scientific
experimental study on heredity. Mendel, an Austrian Augustinian monk
observed variations in the characteristics of garden pea plant (Pisum sativum)
which he had cultivated in his monastery garden.
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Mendel was curious to find out the results of crossing of pea plants with the
variation in traits. The visible contrasting characters that Mendel observed in the
garden pea plants were:-
Seed shape - Round/Wrinkled
Seed color - Yellow/GreenFlower color - Violet / White
Pod shape - Full / Constricted
Pod color - Green / Yellow
Flower position - Axillaries / Terminal
Stem height - Tall / Dwarf
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VARIATIONSThe difference in the characters (or traits) among the individuals of a species iscalledVARIATION.
In most of the people, the earlobes hanging and it is called free earlobe. In
some people, however, the earlobe is closely attached to the side of the head and
it is called attached earlobe.
So, the free earlobes and attached earlobes are the two variations found in
human populations.
The variation is a necessity for organic evolution.
TYPES OF
VARIATIONS
A) Somatic Variation - It pertains to body cells and it is not
inherited.
B) Germinal Variation - It pertains to germ cells or gametes and it is
inheritable. It leads to speciation and evolution.
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Significance of Variation:-
It is the source of raw material for evolution
Animals are able to adapt themselves to the changing environment
Organisms are better suited to face the struggle for existence
Variations give the organisms an individuality of their own
Without variation, there would be no science of heredity as all individuals
of a race, would be identical in all aspects.
ACCUMULATIONThe significance of a variation shows up only if it continues to be inherited by
the offspring for several generations. The great advantage of variation to a
species is that it increases the chances of its survival in a changing environment.
A CHROMOSOME is a thread- like structure in the nucleus of a cell formed
of DNA which carries the genes. A GENES is a unit of aDNA on a
chromosome which governs the synthesis of one protein that controls a specific
characteristic (or traits) from their offspring during reproduction. TheGENEwhich decides the appearance of an organism even in the presence of an
alternative gene is known as a DOMINANT GENE.
The gene which can decide the appearance of an organism only in the presence
of another identical gene is calledRECESSIVE GENE.
The dominant gene is represented by a capital letter and the corresponding
RECESSIVE GENE is represented by the corresponding small letter.
In simple words,GENOTYPE is the description of genes present in an
organism.
The characteristic which is visible in an organism is calledPHENOTYPE.
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Mendels monohybridcrossMendel selected the garden pea plant, Pisum sativum for his experiments. He
selected tall and dwarf plants and allowed them to grow naturally. As pea plants
produce seeds only by self pollination, he observed that tall plants produced
always tall plants generation after generation under natural condition.
Similarly, dwarf plants produced always dwarf plants generation after
generation. Hence, he termed the tall and dwarf plants as wild types or pure
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breeding varieties. Then he crossed a tall plant with a dwarf plant, produced
progeny and calculated the percentage of tallness and darkness in subsequent
generations. When a pure breeding tall plant was crossed with a pure breeding
dwarf plant, all plants were tall in the first filial generation (F1) i.e., there was
not any medium height plants or dwarf plants. This means that only one of theparental traits were seen and not the mixture of the two. When such a F1 tall
plant was allowed to have self pollination, both the tall and dwarf plants
appeared in second filial generation (F2). In the ratio of 3:1. This indicates that
both tallness and darkness were inherited in the F1 plants but only tallness trait
was expressed. The first experiment of Mendel considering the inheritance of a
single trait (Height of the plant Tall/Dwarf) is called Monohybrid Cross.
Expression of morphological characters as tall or dwarf plant, violet or white
flower is called Phenotype. The expression of gene (or Chromosomal make up)of an individual for a particular trait is called Genotype
Physical basis of
heredityThe genotype of a character is influenced by factors, called Genes. The genes are
the factors which form the physical basis for inheritance of Characters. The
alternate expressions of the same gene are called alleles. The contrasting pair of
alleles makes up an allelomorph.
Examples: Tall and dwarf plants, wrinkled and smooth seed coat, white and
violet colored flower. Organisms differ or vary in expressing phenotype whichleads to variation.
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THEORY OF
NATURAL
SELECTION
Charles Darwin made a number of observations in many parts of the world andput forth the law of natural selection involving struggle for existence and
survival of the fittest. Variation leads to genetic diversity, which is the key for
evolution.
Speciation
Mankind in India and all other parts of the world, form a single species called
Homo sapiens. As in India, morphological features of people living in different
geographical areas like South India, North India, North Eastern region,
Kashmir and Andaman are not the same as the people living in different
continents are different in morphological features. Men, with these differences
in their bodily features, differentiate more and more, if there is no chance of
interbreeding among them. When two populations are isolated by geographical
barriers, or reproductive barriers, there is a chance for a change to develop in
their gene flow (Genetic drift), leading to formation of a new species. Genetic
drift with changes in the gene flow imposed by isolation mechanism acts as an
agent of speciation. Thus speciation is arising of a new species from a sub-
population of a species which is geographically or reproductively isolated over a
long period of time from the other population of the same species
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HUMAN
EVOLUTION
Fifteen million years ago, in Africa existed hairy bodied Gorilla and
Chimpanzees like Hominids. After that 3-4 million years ago, men like hominids,
walked into Eastern Africa. Evidence shows that they hunted with stone weapons
but were mostly fruit eaters. They were probably not taller than four feet but,
walked upright in the grass lands of East Africa. These creatures were called the
First human like beingthe hominid. The hominid was called Homo
habilis.The next stage of human evolution came into existence 1.5 million years
ago with the rise of Homo erectus who were meat eaters The Neanderthal man
who lived in East and Central Asia 1 million years ago, used to hide to protect
them and buried their dead. Archaic Homo sapiens arose in South Africa and
moved across continents and developed into distinct races during the ice age.
Between 75,00010,000 years, the modern Homo sapiens arose. Prehistoric
caves were developed about 18,000 years ago, agriculture came around 10,000years back and human settlements started.