Science Project Work 2013

7/29/2019 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.

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Science Project Work 2013