GENETICS AND HEREDITY
Heredity: The passing of traits from the parents to offspring is called heredity. This is heredity which is responsible for many commonly observable facts; like siblings looking similar in overall appearance.
Genotype: The complete set of genes in an organism’s genome is called genotype.
Phenotype: The observable characters in an organism make the phenotype. Phenotype is a result of genotype’s interaction with the environment. Due to this reason, many phenotypes are not inheritable.
Acquired Traits: Traits which are acquired due to interaction with the environment; are called acquired traits. Acquired traits are not inheritable. Inheritable Traits: Traits; which can be expressed in subsequent generations; are called inheritable traits. Such traits bring a change in the genotype of the organism and hence become inheritable.
RULES OF INHERITANCE
Gregor Johann Mendel conducted experiments on pea plants (Pisum sativum) and proposed the rules of inheritance; based on his observations. Mendel observed that characters are often present in pairs. A pair of contrasting characters is called allele.
Possible Reasons of Pea Plants Used by Mendel:
Pea can be termed as biennial plant, i.e. two generations of a pea plant can grow in a given year
Many easily identifiable and contrasting characters are present in pea plants.
Cross pollination can be easily induced in pea plants.
Monohybrid Cross: The cross in which just two contrasting characters are studied is called monohybrid cross. Mendel did monohybrid cross for his first experiment. He selected a pair of contrasting characters for that experiment.
Mendel's First Law- the law of dominance;-
It states that a trait is controlled by two alleles. One allele called the dominant allele inhabits the expression of the resessive allele. This phenomenon is called dominance.
Let us take the example of cross between tall plants and short plants. TT represents the genotype of tall plant and tt represents the genotype of short plants. In the F1 generation, all plants were tall but their genotype was Tt; which means they were not pure tall plants. This could be established by the appearance of the character of shortness in the F2 generation; in which most of the plants were tall and some of the plants were short. This experiment showed that the character of shortness of recessive in F1 generation and hence could not be observed. The ratio of number of tall plants to that of short plants in F2 generation was 3 : 1.
Mendel's secound Law-Law of Segregation: Every individual possesses a pair of alleles for a particular trait. During gamete formation, the two alleles segregate or separate so that a gamete receives only one allele of that trait.(law of purity of gametes). A particular trait can be dominant or recessive in a particular generation. It is shown by monohybrid cross as explained above. The two alleles T and t segregate at the time of gametogenesis in f2 generation.
Mendel’s third Law-Law of Independent Assortment: Alleles of different characters separate or assort independently from each other during gamete formation.
Dihybrid Cross: The cross in which two pairs of characters are studied is called dihybrid cross. In his second experiment, Mendel used dihybrid cross.
Let us take example between plants with round and green seeds and those with wrinkled and yellow seeds. The genotype of round and green seeds is shown by RRyy and that of wrinkled and yellow seeds is shown by rrYY. In the F1 generation, all plants produced round and yellow seeds; which means that wrinkled texture was the recessive character and so was the green colour of seeds. When plants of F1 generation were allowed to self pollinate; it was observed that most of the plants in F2 generation produced round and yellow seeds. Some plants produces round green seeds, some produced wrinkled yellow seeds and some produced wrinkled green seeds. The ratio was 9 : 3 : 3 : 1; as shown in the figure.
SEX DETERMINATION IN HUMANS:- Somatic cells in human beings contain 23 pairs of chromosomes. Out of them the 23rd pair is composed of different types of chromosomes which are named as X and Y chromosomes. The 23rd pair contains one X and one Y chromosome in a male. On the other hand, the 23rd pair in a female contains X chromosomes. This means that all the eggs would have X chromosome as the 23rd chromosome, while a sperm may have either X or Y chromosome as the 23rd chromosome. When a sperm with X chromosome fertilizes the egg, the resulting zygote would develop into a female child. When a sperm with Y chromosome fertilizes the egg, the resulting zygote would develop into a male child.
EVOLUTION
The change in inherited traits in biological population over subsequent generations is called evolution. Scientists have proven that life evolved in the form of simple unicellular organisms on this earth; and all the organisms which are present today have evolved from a common ancestor. The idea of evolution is based on the premise of a common ancestry.
Darwin’s Theory of Evolution:
Charles Darwin wrote his famous book ‘Origin of Species’. He threw new insights on evolution of species. Some salient points of Darwin’s theory are as follows:
1. Organisms have unlimited capacity to reproduce. This is necessary for survival, because a higher number of offspring ensures that at least some of them could survive. Each organism has to struggle for its day to day survival
2. Natural Selection-Different individuals of a particular species have different traits. Those with more suitable traits are selected by the nature. Each organism needs a particular trait for finding food and finding a mate. Those with better traits are finally able to pass on their traits to the next generation.
3. Survival of the Fittest-Those organisms which are the fittest are able to survive, while others perish. That is how many species become extinct and some species continue to evolve over a period of time.
MOLECULAR ORIGIN OF LIFE
Stanley L. Miller and Harold C. Urey, conducted the Miller-Urey experiment in 1953 to demonstrate how the life would have originated on the earth. They created an environment in laboratory which mimicked the environment of earth as it was during the time of origin of life. Water, methane, ammonia and hydrogen were used in that experiment. The liquid was heated to initiate evaporation and electrodes were used to create electric discharge. At the end of two weeks, some organic molecules were formed in the setup. Some amino acids and sugar were also formed. This proved the hypothesis of J. B. S. Haldane that life originated from inorganic raw materials.
SPECIATION
The process of origin of a new species is called speciation. A species is a group of organisms in which most of the characters are similar and members of a species are able to breed among themselves. Speciation can happen if two groups of the same species are somehow prevented from interbreeding for several generations. This can happen because of geographical segregation or because of some genetic changes. Evolution of new species, because of geographical segregation is called genetic drift.
EVOLUTION AND CLASSIFICATION
The modern system of classification is based on evolutionary relationship. Due to this, this is also known as phylogenetic classification. The kingdom is the highest taxa, while the species is the lowest taxa. Members of a species have a higher number of common characters, than members of a kingdom. For example; all human beings belong to the species Homo sapiens.
HOMOLOGOUS ORGANS: Organs which have common design but serve different functions in different animals are called homologous organs. For example; the forelimbs of all tetrapods are composed of humerus, radio-ulna, tarsals and metatarsals. Yet, the forelimbs of frogs are adapted to a jumping movement, those of birds are used for flying and those of humans are used for handling tools. This shows that frogs, birds and humans have evolved from a common ancestor.
ANALOGOUS ORGANS: Organs which have different design but serve a common function in different animals are called analogous organs. Wings of birds and wings of bat are good examples of a pair of analogous organs. Wings of birds are composed of all the bones of forelimb and are covered with feathers. Wings of bats are mainly composed of the digital bones and a thin membrane covering the structure. Yet wings in both the organisms are used for flying.
FOSSILS
The preserved remains of animals or plants or other organisms from the distant past are called fossils. The term distant is a key term in this definition. Scientists usually take 10,000 years as the minimum age for the remains to be categorized as fossil. Many fossils have been discovered till date. These fossils tell us about many extinct animals and also give insights into how the evolution could have taken place.
EVOLUTION BY STAGES
Evolution of complex organs and thus of complex organisms has happened in stages. Let us take the example of evolution of eyes. Planaria is the first animal which shows ‘eye’ like structure. The dark spots on planaria are light sensitive spots but a planaria cannot distinguish between two different objects. Eyes of insects are compound eyes which are made up of thousands of optical surfaces. Eyes of higher animals are simple eyes which are composed of a single lens. Most of the animals cannot differentiate among colours. Depth perception is also weak in many animals. Human eyes are the most advanced; because humans can recognize colours and have very good depth perception.
Most of the tetrapods have to use all the four limbs for locomotion. Some apes can walk up to smaller distances by using just the hind limbs. Humans have finally evolved the bipedal walking.
EVOLUTION VS PROGRESS
Evolution does not mean progress in every case. This can be proved by example of bacteria. Bacteria are the simplest and one of the oldest organisms on the earth. Their simple body design does not make them weak from any angle. Bacteria are known to survive some of the harshest climates; like craters of volcanoes and sulfur springs. Many animals have certain features which hamper even their routine activities. For example; the branch-like horns of antelope are a handicap for them. When an antelope runs for its life; there are times when its horns get entangled in branches or bushes. This results in the death of the antelope. Colourful feathers of a male peacock are very good when it comes to attract a female. But because of its conspicuous feathers, it can be easily spotted by a predator. Because of its bulky feather it cannot fly away to safety.
HUMAN EVOLUTION
The modern humans are called Homo sapiens. Many scientific investigations have shown that the modern humans evolved in Africa. They migrated towards north; in due course of time and settled near what is known as the Mediterranean Sea. When the ice age ended, melting of ice resulted in the in water level. The humans migrated in different directions from that area. One branch went to the western Asia, then to the Indian Peninsula and finally to Australia. From the Indian Peninsula, branch migrated towards China and subsequently to the North America. From North America, the humans migrated to the South America. From the Mediterranean Sea, the second branch migrated towards Europe; where they are believed to replace the Neanderthals.
TEXTUAL QUESTIONS
1. If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?
Answer-Trait B because in asexual reproduction traits which are present in the previous generation are carried over to next generation with minimal variations. Trait B have higher percentage so it is likeliy to have arisen earlier.
2. How does the creation of variations in a species promote survival?
Answer-Variations occur due to sexual reproduction and also due to inaccurate copying of DNA. Depending on the nature of variations, different individuals would have different kinds of advantages. For example, bacteria variants which can withstand heat have better chances to survive in a heat wave non-variant bacteria having no capacity to tolerate heat wave. Thus, variations in a population of a species help in survival of a species.
1. How do Mendel's experiments show that traits may be dominant or recessive?
Answer-The trait which appears in all the members of F1 generation and also in 75% numbers of F2 generation obtained by self fertilization of F1 generation is dominant character.
The trait which does not appear in F generation but after self-fertilization of F1 generation, reappears in 25% of F2 generation is known as recessive.
Answer-Trait B because in asexual reproduction traits which are present in the previous generation are carried over to next generation with minimal variations. Trait B have higher percentage so it is likeliy to have arisen earlier.
2. How does the creation of variations in a species promote survival?
Answer-Variations occur due to sexual reproduction and also due to inaccurate copying of DNA. Depending on the nature of variations, different individuals would have different kinds of advantages. For example, bacteria variants which can withstand heat have better chances to survive in a heat wave non-variant bacteria having no capacity to tolerate heat wave. Thus, variations in a population of a species help in survival of a species.
1. How do Mendel's experiments show that traits may be dominant or recessive?
Answer-The trait which appears in all the members of F1 generation and also in 75% numbers of F2 generation obtained by self fertilization of F1 generation is dominant character.
The trait which does not appear in F generation but after self-fertilization of F1 generation, reappears in 25% of F2 generation is known as recessive.
2. How do Mendel's experiments show that traits are inherited independently?
Answer-Mendel crossed pure breeding tall plants having round seeds with pure breeding short plants having wrinkled seeds. The plants of F1 generation were all tall with round seeds indicating that the traits of tallness and round seeds were dominant. Self breeding of F1 yielded plants with characters of 9 tall round seeded, 3 tall wrinkled seeded , 3 short round seeded and one short wrinkled seeded. Tall wrinkled seeded and short round seeded plants are new combinations which can develop only when the traits are inherited independently.
3. A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits - blood group A or O - is dominant? Why or why not?
Answer-Mendel crossed pure breeding tall plants having round seeds with pure breeding short plants having wrinkled seeds. The plants of F1 generation were all tall with round seeds indicating that the traits of tallness and round seeds were dominant. Self breeding of F1 yielded plants with characters of 9 tall round seeded, 3 tall wrinkled seeded , 3 short round seeded and one short wrinkled seeded. Tall wrinkled seeded and short round seeded plants are new combinations which can develop only when the traits are inherited independently.
3. A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits - blood group A or O - is dominant? Why or why not?
Answer-No. This information is not sufficient to determine which of the traits - blood group A or O - is dominant. This is because we do not know about the blood group of all the progeny.
Blood group A can be genotypically AA or AO. Hence, the information is incomplete to draw any such conclusion.
Blood group A can be genotypically AA or AO. Hence, the information is incomplete to draw any such conclusion.
4. How is the sex of the child determined in human beings?
Answer-In human beings, the females have two X chromosomes and the males have one X and one Y chromosome. Therefore, the females are XX and the males are XY. The gametes, as we know, receive half of the chromosomes. The male gametes have 22 autosomes and either X or Y sex chromosome.
Type of male gametes: 22+X OR 22+ Y.
However, since the females have XX sex chromosomes, their gametes can only have X sex chromosome.
Answer-In human beings, the females have two X chromosomes and the males have one X and one Y chromosome. Therefore, the females are XX and the males are XY. The gametes, as we know, receive half of the chromosomes. The male gametes have 22 autosomes and either X or Y sex chromosome.
Type of male gametes: 22+X OR 22+ Y.
However, since the females have XX sex chromosomes, their gametes can only have X sex chromosome.
Type of female gamete: 22+X
Thus, the mother provides only X chromosomes. The sex of the baby is determined by the type of male gamete (X or Y) that fuses with the X chromosome of the female.
1. What are the different ways in which individuals with a particular trait may increase in a population?
Answer-Individuals with a particular trait may increase in a population as a result of the following:
Natural selection: When that trait offers some survival advantage.
Genetic drift: When some genes governing that trait become common in a population. -When that trait gets acquired during the individual's lifetime.
2. Why are traits acquired during the life-time of an individual not inherited?
Answer-This happens because an acquired trait involves change in non-reproductive tissues which cannot be passed on to germ cells or the progeny. Therefore, these traits cannot be inherited.
3. Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?
Answer-The small number of members in a population of tigers do not allow large number of variation to occur which are essential to survival of the species. A deadly disease or calamity may cause death of all the tigers. The small number of tiger also indicates that existing tiger variants are not well adopted to the existing environment and may extinct soon.
1. What factors could lead to the rise of a new species?
Answer-Natural selection, genetic drift and acquisition of traits during the life time of an individual can give rise to new species.
Natural selection: When that trait offers some survival advantage.
Genetic drift: When some genes governing that trait become common in a population. -When that trait gets acquired during the individual's lifetime.
2. Why are traits acquired during the life-time of an individual not inherited?
Answer-This happens because an acquired trait involves change in non-reproductive tissues which cannot be passed on to germ cells or the progeny. Therefore, these traits cannot be inherited.
3. Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?
Answer-The small number of members in a population of tigers do not allow large number of variation to occur which are essential to survival of the species. A deadly disease or calamity may cause death of all the tigers. The small number of tiger also indicates that existing tiger variants are not well adopted to the existing environment and may extinct soon.
1. What factors could lead to the rise of a new species?
Answer-Natural selection, genetic drift and acquisition of traits during the life time of an individual can give rise to new species.
2. Will geographical isolation be a major factor in the speciation
of a self-pollinating plant species? Why or why not?
Answer-Geographical isolation can prevent the transfer of pollens among different plants. However, since the plants are self-pollinating, which means that the pollens are transferred from the anther of one flower to the stigma of the same flower or of another flower of the same plant, geographical isolation cannot prevent speciation in this case.
3. Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?
Answer-No, because geographical isolation does not affect much in asexually reproducing organisms. Asexually reproducing organisms pass on the parent DNA to offsprings that leaves no chance of speciation. However, geographical isolation works as a major factor in cross pollinated species. As it would result in pollinated species. As it would result in accumulation of variation in the two geographically separated population.
1. Give an example of characteristics being used to determine how close two species are in evolutionary terms.
Answer-Feathers in some ancient reptiles like dinosaurs, as fossils indicate, evolved to provide insulation in cold weather. However, they cannot fly with these feathers later on birds adapted the feathers to flight. This means that birds are very closely related to reptiles, since dinosaurs were reptile.
2. Can the wing of a butterfly and the wing of a bat be considered homologous organs? Why or why not?
Answer-The wing of a butterfly and the wing of a bat are similar in function. They help the butterfly and the bat in flying. Since they perform similar function, they are analogous organs and not homologous.
3. What are fossils? What do they tell us about the process of evolution?
Answer-Fossils are the remains of organisms that once existed on earth.
They tell us about the development of the structures from simple structured to complex structured organisms.They tell us about the phases of evolutions through which they must have undergone in order to sustain themselves in the competetive environment.
1. Why are human beings who look so different from each other in terms of size, colour and looks said to belong to the same species?
Answer-A species is a group of organisms that are capable of interbreeding to produce a fertile offspring. Skin colour, looks, and size are all variety of features present in human beings. These features are genetic but also environmentally controlled. Various human races are formed based on these features. All human races have more than enough similarities to be classified as same species. Therefore, all human beings are a single species as humans of different colour, size, and looks are capable of reproduction and can produce a fertile offspring.
2. In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a 'better' body design? Why or why not?
Answer-Evolution cannot always be equated with progress or better body designs. Evolution simply creates more complex body designs. However, this does not mean that the simple body designs are inefficient. In fact, bacteria having a simple body design are still the most cosmopolitan organisms found on earth. They can survive hot springs, deep sea, and even freezing environment. Therefore, bacteria, spiders, Excercise
1. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as ► (c) TtWW
2. An example of homologous organs is ► (b) our teeth and an elephant's tusks.
3. In evolutionary terms, we have more in common with► (a) a Chinese school-boy.
4. A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?
Answer-This information is not sufficient. For considering a trait as dominant or recessive, we need data of at least three generations. This data is about only two generations.
5. How are the areas of study - evolution and classification - interlinked?
Answer-Classification involves grouping of organism into a formal system based on similarities in internal and external structure or evolutionary history.
Two species are more closely related if they have more characteristics in common. And if two species are more closely related, then it means they have a more recent ancestor. For example, in a family, a brother and sister are closely related and they have a recent common ancestor i.e., their parents. A brother and his cousin are also related but less than the sister and her brother. This is because the brother and his cousin have a common ancestor i.e., their grandparents in the second generation whereas the parents were from the first generation. With subsequent generations, the variations make organisms more different than their ancestors. This discussion clearly proves that we classify organisms according to their resemblance which is similar to creating an evolutionary tree.
6. Explain the terms analogous and homologous organs with examples.
Answer-Homologus organs are those organs which have the same basic structural design and origin but have different functions. e.g The forelimbs of humans and the wings of birds look different externally but their skeletal structure is similar.
3. Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?
Answer-No, because geographical isolation does not affect much in asexually reproducing organisms. Asexually reproducing organisms pass on the parent DNA to offsprings that leaves no chance of speciation. However, geographical isolation works as a major factor in cross pollinated species. As it would result in pollinated species. As it would result in accumulation of variation in the two geographically separated population.
1. Give an example of characteristics being used to determine how close two species are in evolutionary terms.
Answer-Feathers in some ancient reptiles like dinosaurs, as fossils indicate, evolved to provide insulation in cold weather. However, they cannot fly with these feathers later on birds adapted the feathers to flight. This means that birds are very closely related to reptiles, since dinosaurs were reptile.
2. Can the wing of a butterfly and the wing of a bat be considered homologous organs? Why or why not?
Answer-The wing of a butterfly and the wing of a bat are similar in function. They help the butterfly and the bat in flying. Since they perform similar function, they are analogous organs and not homologous.
3. What are fossils? What do they tell us about the process of evolution?
Answer-Fossils are the remains of organisms that once existed on earth.
They tell us about the development of the structures from simple structured to complex structured organisms.They tell us about the phases of evolutions through which they must have undergone in order to sustain themselves in the competetive environment.
1. Why are human beings who look so different from each other in terms of size, colour and looks said to belong to the same species?
Answer-A species is a group of organisms that are capable of interbreeding to produce a fertile offspring. Skin colour, looks, and size are all variety of features present in human beings. These features are genetic but also environmentally controlled. Various human races are formed based on these features. All human races have more than enough similarities to be classified as same species. Therefore, all human beings are a single species as humans of different colour, size, and looks are capable of reproduction and can produce a fertile offspring.
2. In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a 'better' body design? Why or why not?
Answer-Evolution cannot always be equated with progress or better body designs. Evolution simply creates more complex body designs. However, this does not mean that the simple body designs are inefficient. In fact, bacteria having a simple body design are still the most cosmopolitan organisms found on earth. They can survive hot springs, deep sea, and even freezing environment. Therefore, bacteria, spiders, Excercise
1. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as ► (c) TtWW
2. An example of homologous organs is ► (b) our teeth and an elephant's tusks.
3. In evolutionary terms, we have more in common with► (a) a Chinese school-boy.
4. A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?
Answer-This information is not sufficient. For considering a trait as dominant or recessive, we need data of at least three generations. This data is about only two generations.
5. How are the areas of study - evolution and classification - interlinked?
Answer-Classification involves grouping of organism into a formal system based on similarities in internal and external structure or evolutionary history.
Two species are more closely related if they have more characteristics in common. And if two species are more closely related, then it means they have a more recent ancestor. For example, in a family, a brother and sister are closely related and they have a recent common ancestor i.e., their parents. A brother and his cousin are also related but less than the sister and her brother. This is because the brother and his cousin have a common ancestor i.e., their grandparents in the second generation whereas the parents were from the first generation. With subsequent generations, the variations make organisms more different than their ancestors. This discussion clearly proves that we classify organisms according to their resemblance which is similar to creating an evolutionary tree.
6. Explain the terms analogous and homologous organs with examples.
Answer-Homologus organs are those organs which have the same basic structural design and origin but have different functions. e.g The forelimbs of humans and the wings of birds look different externally but their skeletal structure is similar.
Analogus organs are those organs which have the different basic structural design and origin but have similar functions. For Example: The wings of birds and insects.
7. Outline a project which aims to find the dominant coat colour in dogs.
Answer-Dogs have a variety of genes that govern coat colour. There are at least eleven identified gene series (A, B, C, D, E, F, G, M, P, S, T) that influence coat colour in dog. A dog inherits one gene from each of its parents. The dominant gene gets expressed in the phenotype. For example, in the B series, a dog can be genetically black or brown. Let us assume that one parent is homozygous black (BB), while the other parent is homozygous brown (bb) In this case, all the offsprings will be heterozygous (Bb).
Since black (B) is dominant, all the offsprings will be black. However, they will have both B and b alleles.
If such heterozygous pups are crossed, they will produce 25% homozygous black (BB), 50% heterozygous black (Bb), and 25% homozygous brown (bb) offsprings.
7. Outline a project which aims to find the dominant coat colour in dogs.
Answer-Dogs have a variety of genes that govern coat colour. There are at least eleven identified gene series (A, B, C, D, E, F, G, M, P, S, T) that influence coat colour in dog. A dog inherits one gene from each of its parents. The dominant gene gets expressed in the phenotype. For example, in the B series, a dog can be genetically black or brown. Let us assume that one parent is homozygous black (BB), while the other parent is homozygous brown (bb) In this case, all the offsprings will be heterozygous (Bb).
Since black (B) is dominant, all the offsprings will be black. However, they will have both B and b alleles.
If such heterozygous pups are crossed, they will produce 25% homozygous black (BB), 50% heterozygous black (Bb), and 25% homozygous brown (bb) offsprings.
8. Explain the importance of fossils in deciding evolutionary relationships.
Answer-Fossil provide us evidence about
→ The organisms that lived long ago such as the time period during which they lived, their structure etc.
→ Evolutionary development of species i.e., line of their development.
→ Connecting links between two groups. For example, feathers present in some dinosaurs means that birds are very closely related to reptiles.
→ Which organisms evolved earlier and which later.
→ Development of complex body designs from the simple body designs.
9. What evidence do we have for the origin of life from inanimate matter?
Answer-The evidence for the origin of life from inanimate matter, was provided through an experiment, conducted in 1953, by Stanley L. Miller and Harold C. Urey. In experiment, they assembled an atmosphere containing molecules like ammonia, methane and hydrogen sulphide, but no oxygen, over water. This was similar to atmosphere that thought to exist on early earth . This was maintained at a temperature just below 100°C and sparks were passed through the mixture of gases to simulate lightning. At the end of a week, 15% of the carbon from methane, had been converted to simple compounds of carbon including amino acids which make up protein molecules and support the life in basic form. Thus, amply suggesting that life arose afresh on earth.
Answer-Fossil provide us evidence about
→ The organisms that lived long ago such as the time period during which they lived, their structure etc.
→ Evolutionary development of species i.e., line of their development.
→ Connecting links between two groups. For example, feathers present in some dinosaurs means that birds are very closely related to reptiles.
→ Which organisms evolved earlier and which later.
→ Development of complex body designs from the simple body designs.
9. What evidence do we have for the origin of life from inanimate matter?
Answer-The evidence for the origin of life from inanimate matter, was provided through an experiment, conducted in 1953, by Stanley L. Miller and Harold C. Urey. In experiment, they assembled an atmosphere containing molecules like ammonia, methane and hydrogen sulphide, but no oxygen, over water. This was similar to atmosphere that thought to exist on early earth . This was maintained at a temperature just below 100°C and sparks were passed through the mixture of gases to simulate lightning. At the end of a week, 15% of the carbon from methane, had been converted to simple compounds of carbon including amino acids which make up protein molecules and support the life in basic form. Thus, amply suggesting that life arose afresh on earth.
10. Explain how sexual reproduction gives rise to more viable variations than asexual reproduction. How does this affect the evolution of those organisms that reproduce sexually?
Answer-Sexual reproduction causes more viable variations due to the following reasons: → Error in copying of DNA, which are not highly significant.→ Random seggregation of paternal and maternal chromosome at the time of gamete formation.
→ Exchange of genetic material between homologous chromosomes during formation of gametes. → Accumulation of variations occured due to sexual reproduction over generation after generation and selection by nature created wide diversity. In case of asexual reproduction, only the very small changes due to inaccuracies in DNA copying pass on the progeny. Thus, offsprings of asexual reproduction are more or less genetically similar to their parents. So, it can be concluded that evolution in sexually reproducing organisms proceeds at a faster pace than in asexually repoducing organisms.
11. How is the equal genetic contribution of male and female parents ensured in the progeny?
Answer-In human beings, equal genetic contribution of male and female parents is ensured in the progeny through inheritance of equal number of chromosomes from both parents. There are 23 pairs of chromosomes All human chromosomes are not paired. Out of these 23 pairs, the first 22 pairs are known as autosomes and the remaining one pair is known as sex chromosomes represented as X and Y. Females have a perfect pair of two X sex chromosomes and males have a mismatched pair of one X and one Y sex chromosome.
During the course of reproduction, as fertilization process takes place, the male gamete (haploid) fuses with the female gamete (haploid) resulting in formation of the diploid zygote. The zygote in the progeny receive an equal contribution of genetic material from the parents. Out of 23 pairs of chromosomes in progeny, male parent contributes 22 autosomes and one X or Y chromosome and female parent contributes 22 autosomes and one X chromosome.
12. Only variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement? Why or why not?
Answer-We agree with the statement that Only variations that confer an advantage to an individual organism will survive in a population. All the variations do not have an equal chance of surviving in the environment in which they find themselves. The chances of surviving depend on the nature of variations. Different individual would have different kind of advantages. A bacteria that can withstand heat will survive better in a heat wave. Selection of variants by environmental factors forms the basis for revolutionary process.
Answer-Sexual reproduction causes more viable variations due to the following reasons: → Error in copying of DNA, which are not highly significant.→ Random seggregation of paternal and maternal chromosome at the time of gamete formation.
→ Exchange of genetic material between homologous chromosomes during formation of gametes. → Accumulation of variations occured due to sexual reproduction over generation after generation and selection by nature created wide diversity. In case of asexual reproduction, only the very small changes due to inaccuracies in DNA copying pass on the progeny. Thus, offsprings of asexual reproduction are more or less genetically similar to their parents. So, it can be concluded that evolution in sexually reproducing organisms proceeds at a faster pace than in asexually repoducing organisms.
11. How is the equal genetic contribution of male and female parents ensured in the progeny?
Answer-In human beings, equal genetic contribution of male and female parents is ensured in the progeny through inheritance of equal number of chromosomes from both parents. There are 23 pairs of chromosomes All human chromosomes are not paired. Out of these 23 pairs, the first 22 pairs are known as autosomes and the remaining one pair is known as sex chromosomes represented as X and Y. Females have a perfect pair of two X sex chromosomes and males have a mismatched pair of one X and one Y sex chromosome.
During the course of reproduction, as fertilization process takes place, the male gamete (haploid) fuses with the female gamete (haploid) resulting in formation of the diploid zygote. The zygote in the progeny receive an equal contribution of genetic material from the parents. Out of 23 pairs of chromosomes in progeny, male parent contributes 22 autosomes and one X or Y chromosome and female parent contributes 22 autosomes and one X chromosome.
12. Only variations that confer an advantage to an individual organism will survive in a population. Do you agree with this statement? Why or why not?
Answer-We agree with the statement that Only variations that confer an advantage to an individual organism will survive in a population. All the variations do not have an equal chance of surviving in the environment in which they find themselves. The chances of surviving depend on the nature of variations. Different individual would have different kind of advantages. A bacteria that can withstand heat will survive better in a heat wave. Selection of variants by environmental factors forms the basis for revolutionary process.
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