Content Curator
Genes can be defined as functional units of inheritance (heredity). According to CBSE Class 10 Chapter 9 Heredity and Evolution, each gene is responsible for controlling one or more characteristic traits in different living organisms. Heredity can be defined as the process by which various properties of an organism are passed on from one generation to another.
According to Gregor Johann Mendel, there are three laws that are the basics of inheritance. These laws are:
Law of Dominance
According to the law of dominance, a gene that has two opposing alleles and of which the only gene is always expressed is called the dominant gene.
Law of segregation
The law of segregation states that features are completely separated during gamete formation without the alleles mixing.
Law of Independent assortment
According to the law of independent sorting, features can be separated from different characters independently, which occurs during the process of formation of gamete.
Mendel’s Pea Experiment
The study of heredity, or how some characteristics are inherited from father to offspring, had long puzzled scientists. Many scientists questioned what causes characteristics to pass from one generation to another; why are some characteristics inherited and others not?
To better understand this, Mendel began to study peas. He took pea plants with different traits (tall/short, green/yellow etc.) and began to breed offspring from them, noting if any traits were inherited. In this first-generation, or F1 progeny, all received tall plants. However, the second generation or the F2 offspring obtained by growing first-generation plants were not all large, but a quarter(1 out of 4) were small.
Read More About Rules for the Inheritance of Traits - Mendel's Contributions
Gender Determination
Let us now examine how gender is determined in humans. A human being has a total of 23 pairs of chromosomes, 1 pair (sex chromosomes) is different in men and women; Females have two X chromosomes in this pair, while males have an X and a Y chromosome. So, a baby always gets the X chromosome from the mother, while it gets an X or Y chromosome from the father. The XY combination results in a boy child, XX is a girl child.
Acquired and Inherited Traits
A trait of an individual that is not inherited from parents but develops in response to the environment is called an acquired trait. For example, learning to play sports is a quality that a person acquires throughout their life. They are not born with this quality and therefore cannot pass it on to the next generation. Only those properties can be passed on to the next generation in which changes in the genes or the DNA of the organism have occurred. These properties are known as inherited traits. For example eye color, hair, diseases, etc.
Specialization
A species is a population of organisms made up of similar individuals that can reproduce together and produce offspring. For example, all humans belong to the same species; But humans and dogs are different species. Scientists have determined that there are several factors that lead to the formation of new species, a process known as speciation. These factors can be: The geographical isolation of a population of a particular species (for example, due to mountain ranges, rivers, or the sea) genetic drift (caused by drastic changes in the frequencies of a particular gene that occur randomly) variations due to natural selection etc.
Homologous and Analogous Organs
Various biological studies have shown us that living organisms have undergone changes in their organization since their formation in order to evolve into new forms.
One way to analyze how closely two organisms are related is to look at their organs. Some organisms share the same structure as some organs, but use them for the same or different purposes. These organs are called homologous organs. Frog, lizard, human, and bird, Please note that these all have different functions - a man's limbs are used for grasping, Frogs use them for jumping, lizards use them for running, On the other hand, some organs may have different structures, but they are used for the same thing. These organs are called analog organs. For example, the wings of a bat and that of a bird.
Read More About Sexual and Asexual Reproduction
HEREDITY AND EVOLUTION: IMPORTANT QUESTIONS
Ques. Define the term 'evolution' and Describe Darwin's theory of evolution.
Ans. Evolution is the sequence of gradual changes that take place in primitive organisms over millions of years and from which new species emerge. Since evolution is about living organisms, it is called "Organic evolution".
Darwin's Theory of Evolution
Charles Robert Darwin introduced the Theory of Evolution in his famous book ‘The Origin of Species’. Darwin's theory of evolution is known as the Theory of Natural Selection. It is also called "Darwinism".
According to Darwin's theory of evolution, there are natural variations within any population and some individuals have more favorable variations than others. The population remains fairly constant even though all species produce a large number of sources due to "competition" or struggle for existence between the same and different species. The struggle for survival within the population eliminates unsuitable individuals and those with "favorable variations" survive and pass these variations on to their offspring. This is called natural selection. Favorable variations accumulate over a long period of time, leading to the emergence of a new species.
Ques. Define Variation in relation to a Species. Why is variation beneficial to a species?
Ans.Variation refers to differences in characters or traits between individuals of a species.
Benefits:
- They allow organisms to adapt to changing environments.
- Deviations from the basis of inheritance.
- They form the raw material for the evolution and development of new species.
Ques. What are fossils? What are they telling us about the evolutionary process?
Ans.The remains of dead plants and animals that were buried under rocks millions of years ago are known as fossils. Fossils tell us about the evolutionary process that different organisms have some characteristics similar to one species while some characteristics are similar to those of the other species; In this way, they show the connection between the two species, they tell us that one species evolves from the other.
Ques. People who look so different in color, size, and appearance belong to the same species. Why? Justify your answer.
Ans. Humans are said to belong to the same species for the following reasons:
- DNA studies.
- The number of chromosomes is the same.
- They all have a common ancestor.
- They crossbreed to produce fertile offspring of their own kind.
Ques. Explain, with examples, how the following evidence is for the evolution of organisms: (i) Homologous Organs (ii) Analogous Organs (iii) Fossils
Ans. (i) The front legs of humans and birds are homologous organs. They have the same construction structure and development origin, but different functions and appearance. Homologous organs help us understand that the organism evolved from a common ancestor. The more common features the two species have, the more closely related they are.
(ii) Analogous organs are designed and developed, but have a similar appearance and function. Example: The wings of birds and bats look similar, but have a different design in their structure. They have a common flight function, but their origins are not common.Hence, birds and bats are not closely related.
(iii) Fossils and their study are useful in understanding the species that are no longer alive. They provide evidence and missing links between the two classes. They are useful for building a sequence of organisms. Hence, fossils play a role in deciding the evolutionary relationship. Archeopteryx is a fossil bird. It had feathers, fused bones, and a beak that were all bird structures. It also had some features found in reptiles such as teeth on the jaw, claws on the free fingers, and a long tail. This fossil gives an indication that birds evolved from reptiles.
Ques. Explain the terms: (I) Speciation and (ii) Natural selection
Ans. (i) Speciation is the evolution of reproductive isolation between once interbreeding populations, that is, the development of one or more species from an existing species
(ii) According to Darwin, Natural Selection is the process that brings about the evolution of new animal and plant species.
Ques. What do you mean by human evolution?
Ans.Humans belong to the primate family and the history of human evolution stretches back to the African continent. According to studies, the evolution of humans took place in the following chain:
Dryopithecus to
Ramapithecus to
Australopithecus to
Homo erectus to
Homo neanderthalensis to
Cro Magnon man to
Homo sapiens.
Ques. What is the term speciation? Name four factors that can lead to speciation.
Ans. Speciation is the development of reproductive isolation within a population that was once formed by crossbreeding.
Factors that can lead to speciation are:
- Genetic drift may lead to speciation
- Natural selection can function differently in different places, which can lead to speciation.
- Severe DNA changes
- Variations may occur that do not allow sexual intercourse between two groups.
Ques. Indicate the meaning of inherited and acquired traits, which of the two are not passed on to the next generation? Explain using an example.
Ans. Inherited traits are those traits passed from parents to their offspring.
Acquired traits are traits that develop over the course of an individual's life. Acquired traits are not passed on to the next generation.
Example: Mice, all of their offspring bear tails. If the tails of these mice are surgically removed and allowed to reproduce, the next generation of mice will have tails too. If these tails are also removed and allowed to reproduce, the offspring of the mice will have tails again. Cells are therefore not passed on to the next generation.
Ques. "Organs or functions can adapt to fulfill a new function during evolution." Justify this statement with an example.
"Older body designs are not inefficient." Give a suitable example to support this point of view.
Ans. Many organs and features were created by modifying existing structures.The limbs developed from the lobed fins of the lungs. The wings evolved from the front legs of birds and bats. The feathers that became part of the birds' wings and body covering had already developed in dromaeosaurs. Bacteria continue to live comfortably and competitively in most habitats, even though their body design is very old and very simple compared to the more modern and elaborate body design of aquatic insects or fish. Therefore, older body designs are neither inferior nor ineffective.
Ques. A large plant with dominant height and purple flowers crossed with another plant with recessive, dwarf white flowers
- What do the plants of the F1 generation look like?
- What kind of cross is it?
- What are the phenotype ratio in the F2 generation and name the kind of plants obtained according to the phenotype ratio.
Ans. (a) All tall purple flowers,
(b) Dihybrid hybrid,
(c) Nine tall purple flowers: Three tall white flowers: Three dwarf and purple flowers: One dwarf and white flowers.
Ques. (a)Name an animal that can change sex. What is indicating?
(B) Explain the importance of fossils in the evolutionary relationship.
Ans. (a) Ophryotrocha - males at birth and converts to female later. Gender reassignment indicates that it is not genetic.
(b) Significance for evolution:
Flora and Fauna: Fossils represent flora and fauna of different ages. Early fossils were of very simple plants and animals. The increasingly complex fossils of plants and animals belong to later times.
Descent with Modification: The study of fossils shows that plants and animals of age appear as descendants of plants and animals.
The study of fossils has shown that birds evolved from reptiles or how seed plants evolved from ferns. Fossils have revealed the evolutionary stages of some organisms.
Ques. (A)Marriage between cousins is taboo in most countries of the world except for some Asian countries.
(B) What steps will you take to prevent such practices?
Ans.(a) Marriage between close cousins is similar to inbreeding. The recessive traits (from genetic defects) present in such families become homozygous and cause incurable diseases.
(b) Actions: Selecting families where cousin marriages are common, select their children who go to school and hold seminars or discussions on the illegal effects of marriage on close relatives that include those children. Cousin marriages often occur when early marriages are practiced. Families should be advised to enable their children to go to higher education. These educated people will learn about the flaws in close cousin marriages.
Ques. a) What is the approximate ratio that will be obtained in generation F2?
(b) Under what law do you find this reason?
(c) Why is this law called that?
Ans. (a) 3: 1
(b) Law of the Segregation or Principle of the purity of gametes
(c) The Law of Segregation is so well known because the two factors or alleles of a character separate and pass to different gametes at the time of gametogenesis. A gamete is just one factor of a character. They differ from analogous organs.
Ques. (a) What is geographic isolation?
(b) Use an example to illustrate the formation of a species in which individuals are very different and can reproduce with one another.
Ans. (a) Geographic isolation: Prevention of mating between breeding groups due to geographical or physical barriers (e.g. valley, mountain, water) is called geographical isolation. Isolated populations develop different variations and changes in physiology and behavior to form new species.
(b) More than 160 dog breeds have emerged through selective breeding and artificial selection. There are also about 800 breeds of cattle, which differ in size, height, characteristics, behavior, color, and other characteristics. However, all dogs belong to a species of Canis familiaris, while all cattle belong to a species of Bos indiens. Despite their structural and behavioral differences, all breeds of the same species can cross breed and produce fertile offspring. In spatial isolation, these different breeds can develop reproductive isolation and form new species, e.g. Porto Santo rabbits, Galapagos finches.
Read More:
Comments