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Heredity and EvolutionChapter 9 Biology

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INTRODUCTION A recognizable feature of a human being ( or any other organism) like height, complexion, shape of nose and chin, colour of eye and hair etc are called characters or traits. The transmission of traits from the parents to their offspring is called heredity. The hereditary information is present in the gametes of the parents. Thus, gametes constitute the link between one generation and the next, and pass on the maternal and paternal characters or traits to the offspring.

variations

The differences in the characters (or traits) among the individuals of a species is called variation. The offspring is never a true copy of the parent.

There are many kinds of variations in human species like:- Free and attached earlobes.Different complexions ( Dark, Light brown, Dusky, Wheatish, Fair etc.)Different eye colour ( Brown, Hazel, Blue, Green, Grey, Amber etc.)Height ( tall or short) Chin (cleft or pointed) Hair colour ( Black, Brown, Blonde, Red, Golden etc.) Hair type ( curly, wavy, Straight etc.) Nose ( Snub, Thin, Pointed etc.) Hazel eye colour Blue eye colour

Blonde HairBrown Hair

Accumulation ofVariations

The 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.

Important terms Chromosome : It is a thread-like structure in the nucleus of a cell formed of DNA which carries the genes. Gene : It is a unit of DNA on chromosome which governs the synthesis of one protein that controls a specific characteristic of an organism. Genes are actually units of heredity which transfer characteristics from parents to their offsprings during reproduction. Dominant Gene : The gene which decides the appearance of an organism even in the presence of an alternative contrasting gene is known as a dominant gene. It is represented by a capital letter. Recessive gene : The gene which can decide the appearance of an organism only in the presence of another identical gene is called a recessive gene. It is represented by the corresponding small letter. Genotype : It is the description of genes present in an organism. Phenotype : It is the characteristic which is visible in an organism . First Filial Generation or F1 Generation : When two parents cross to produce offsprings, their offspring is called First Filial generation or F1 generation. Second Filial Generation or F2 Generation : When the first generation offsprings cross among themselves to produce second generation offsprings, then this offspring is called Second Filial Generation or F2 Generation.

Mendels experiments

Gregor Mendel was the first scientist to make a systematic study of patterns of inheritance which involved the transfer of characteristics from parents to progeny.

Mendel chose pea plants for studying inheritance because pea plants had a number of clear cut differences which were easy to tell apart. For ex : tall and dwarf pea plants. Some pea plants produced round yellow seeds while others produced wrinkled green seeds etc.

Another reason for choosing pea plants was that they were self pollinating. Also, Mendel chose pea plants because many generations of pea plants can be produced in a comparatively short time span and their study is much simpler than that of animals.

Law of segregationMendel's first law of inheritance or the Law of Segregation : The characteristics (or trait) of an organism are determined by internal factors which occur in pairs. Only one such factor can be present in a single gamete.

Law of independentassortmentMendels second law of inheritance or Law of Independent Assortment states that In the inheritance of more than one pair of traits in a cross simultaneously, the factors responsible for each pair of traits are distributed independently to the gametes.

Transmission of traitsThe characteristics or traits of parents are transmitted to their offsprings through genes present on their chromosomes during the process of sexual reproduction.

Genes work in pairs. For every trait there is a pair of genes ( one dominant and one recessive). Each parent passes only one of the two genes of the pair for each characteristic.

Though the offspring inherits two genes for each trait from its parents but the trait shown by the offspring depends on which inherited gene is dominant of the two.

genes When a male gamete fuses with a female gamete during fertilization, they make a new cell called zygote with a full set of genes (on a full set of chromosomes) . This zygote grows & develops to form a new organism having characteristics (or traits) from both the parents which it has inherited through genes. The two genes (or pair of genes) responsible for a particular characteristics are always present on the corresponding positions of the pair of chromosomes .

Blood groups A person has one of the four blood groups: A, B, O, AB. A and B are co-dominant genes whereas O is a recessive gene. The genes for blood groups are denoted by: IA ( A in superscript), IB etc. If the genotype is IA IA or IA IO, then the blood group is A. If the genotype is IB IB or IB IO, then the blood group is B.If the genotype is IO IO, then the blood group is O.

Sex determinationThe process by which the sex of a person is determined is called sex determination . The chromosomes which determine the sex of a person are called sex chromosomes . Sex chromosome in male is XY and in female it is XX If a sperm carrying X chromosome fertilizes an ovum then the child born will be a girl .If a sperm carrying Y chromosome fertilizes an ovum then the child born will be a boy .It is the sperm which determines the sex of a child .

Acquired and inheritedtraits A trait of an organism which is not inherited but develops in response to the environment is called an acquired trait. Acquired traits cannot be passed on to the future generations. Ex: Knowledge of doing something or any characteristic which was caused due to environmental factors and not present by birth .

A trait of an organism which is caused by a change in its DNA or genes is called an inherited trait. These are characteristics which we receive from our parents. Only these traits can be transmitted to future generations. Ex: Eye colour, skin complexion etc.

QUESTIONSThe epidermal cell of a plant contains 28 chromosomes. How many chromosomes are there in each gamete produced by the plant?

2. A pure tall pea plant (TT) is crossed with a pure dwarf plant (tt). What is the ratio of pure tall plants to pure short plants in the F2 generation?

3. What are the visible characters in an organism known as? 4. Which of the following is an inherited traits? eye color, scarred face, skin complexion, hair texture, size of body.

5. What are the phenotypes of the following types of hybrid pea seeds. (a) Rryy (b) rrYy (c) RrYy (d) RRyy

ANSWERS14 chromosomes

1:1

3. Phenotype

Eye color is an inherited trait. Scarred face is not an inherited trait Skin complexion is an acquired trait, but environmental factors can also affect skin complexion of a person. Hair texture is an inherited trait, but it can be altered manually. Size of body is not an inherited trait.

(a) Round Green (b) Wrinkled Yellow (c) Round Yellow (d) Round Green

EVOLUTIONEvolution is the sequence of gradual changes which take place in the primitive organisms over millions of years in which new species are produced.

The more characteristics a species have in common, the more closely they will be related.

Some important sources which provide evidence for evolution are Homologous, Analogous, Vestigial organs and fossils.

Archaeopteryx which is believed to be the missing link between dinosaurs and birds.

HOMOLOGOUS ORGANSHomologous organ : Organs which have same fundamental structures but different in functions. Ex: wings of birds , hands of humans.

ANALOGOUS ORGANSAnalogous organs : Organs which similar functions but different in their structure. Ex: wings of insects and wings of birds

Vestigial organsVestigial organs : Organs which are nonfunctional in the present day forms but were functional in ancestors. Ex: appendix, wisdom tooth .

The remains of dead animals or plants that lived in the remote past are known as Fossils. Fossils are obtained by digging into the Earth. The age of fossils are estimated by the relative method or carbon dating method.There are various kinds of fossils. Some important fossils are ammonite, trilobite and dinosaur.

DARWINS THEORYDarwins theory can be described as follows: Within any population, there is natural variation. Some individuals have more favorable variations than others. Even though all species produce a large number of offsprings, populations remain fairly constant naturally. This is due to the struggle between members of the same species and different species for food, space and mate. The struggle for survival within populations eliminates the unfit individuals. The fit individuals possessing favorable variations survive and reproduce. This is called natural selection. The individuals having favorable variations pass on these variations to their progeny from generation to generation. These variations when accumulated over a long period of time, lead to the origin of new species.

NATURAL SELECTIONNatural selection is the process of evolution of a species whereby characteristics which help individual organisms to survive and reproduce are passed on to their offsprings, and those characteristics which do not help are not passed on.

Though Darwins theory was widely accepted, but it was criticized on the ground that it could not explain how the variations arise. With the progress in genetics, the source of variation was explained to be the Genes. Genes vary in natural population. Genetic variation is the raw material of evolution. So, Darwins theory was modified accordingly. These days, the most accepted theory of evolution is the Synthetic theory of evolution. In which the origin of species is based on both genetic variation and natural selection .

SPECIATIONA species is a population of organisms consisting of similar individuals which can breed together and produce fertile offspring.

The process by which new species develop from existing species is known as speciation.

Important factors which could lead to formation of new species are: Geographical isolation of a population which leads to reproductive isolation due to which there is no flow of genes between separated groups of population. Genetic drift due to drastic changes in the frequencies of particular genes by chance alone. Variations caused in individuals due to natural selection.

EVOLUTION OF EYESThe eye is a complicated organ which cannot be generated by a single DNA change.The complex body organs of animals such as eyes have been created in stages over many generations.First of all the basic eye like that of a flatworm which are simple eyespots which can detect light.After this, more and more complex eyes were evolved in many organisms.The structure of eyes in each organism is different.The evolution of eye is an example of evolution by stages.

EVOLUTION OF FEATHERSSometimes an evolutionary change produced in an organism for one purpose later on becomes more useful for an entirely different function.

For ex: Birds evolved feathers as a means of providing insulation to their bodies in cold weather but later on these feathers became more useful for the purpose of flying. Even some dinosaurs had feathers though they could not fly using feathers. Birds, however adapted feathers for flying. The presence of feathers on birds tell us that birds are closely related to dinosaurs.

EVOLUTION BY ARTIFICIALSELECTIONDifferent looking organisms can be created from the same basic design of the ancestors.This is called Evolution by artificial selection.For ex: Cabbage, broccoli, cauliflower, kohlrabi and kale can be made artificially from wild cabbage.

When farmers wanted very short distances between the leaves of wild cabbage, the common variety of cabbage was evolved. When farmers wanted arrested flower development of wild cabbage, broccoli was evolved. When farmers wanted sterile flowers of wild cabbage, cauliflower was evolved. When farmers wanted swollen parts of wild cabbage, kohlrabi was evolved. When farmers wanted to grow large leaves of wild cabbage, kale was evolved.

EVOLUTION IS NOT PROGRESSThere is no real progress in the concept of evolution. Evolution is just the production of diversity of life forms and shaping of this diversity by environmental selection. The only progress in evolution is that more and more complex organisms have emerged over ages.

It is a common belief that chimpanzees are the ancestors of human beings. This is not true. Actually, both chimpanzees and human beings had a common ancestor long time ago.

HUMAN EVOLUTIONHuman evolution has been studied using various tools of tracing evolutionary relationships like excavating, carbon-dating, studying fossils and determining DNA sequences.

All human beings are a single species called Homo Sapiens.It has now been established by research that the earliest members of the human species came from Africa. So, irrespective of where we have lived for past thousand years, we all have African roots.

ORIGIN OF LIFEDarwins theory of evolution tells us how life evolved from simple to more complex forms and Mendels experiments give us the mechanism for the inheritance of traits from one generation to the next. But neither tells us anything about how life began on earth in the first place.

QUESTIONSWhich variety of cabbage evolved due to the farmers opting for swollen parts of wild cabbage?

What is the science of heredity known as?

3. What is the scientific names of humans?

4. State one characteristic which shows tat birds are closely related to dinosaurs.

5. Name the animal which was the link between reptiles and birds.

6. Did human beings evolve from chimpanzees ? Why / Why not ?

7. Name one way how the age of fossils are estimated.

ANSWERSKohlrabi.

Genetics

Homo sapiens

Some dinosaurs had feathers though they could not fly using these feathers. The presence of feathers on birds tell us that the birds are closely related to dinosaurs.

Archaeopteryx

Human beings have not evolved from chimpanzees. Actually, both human beings and chimpanzees had a common ancestor a long time ago.

Carbon-dating method or Relative method.

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Made By:AthiraHrutubalaKeerthiNeha HrishitaaAmeesha