Heredity and Evolution Class 10 Notes Science Chapter 9

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heredity and evolution class 10 notes science chapter 9
heredity and evolution class 10 notes science chapter 9

Heredity and Evolution Class 10 Notes, here we are going to give you a summary of Heredity and Evolution Class 10 Notes. In this chapter we will study about the heredity laws and explanations. We will also learn about fossils and evolution. Your all doubts from the chapter of Heredity and Evolution Class 10 Notes will be cleared from this summary.

Heredity and Evolution Class 10 Notes : Introduction

Reproductive processes give rise to new individuals that are similar, but subtly different. We know that some amount of variation is produced even during asexual reproduction. A number of successful variations are maximised by the process of sexual reproduction.

We are going to study the mechanism by which variations are created and inherited in this chapter. The long-term consequences of the accumulation of variations are also an interesting point to be considered.

Accumulation of variation during reproduction

Inheritance from the previous generation provides both a common basic body design, and subtle changes in it, for the next generation. The second generation will have differences that they inherit from the first generation, as well as newly created differences.

All the variations in a species do not have equal chances of surviving in the environment in which they find themselves. Different individuals would have different kinds of advantages in different environments.

Heredity

The rules of heredity determine the process by which traits and characteristics are reliably inherited.

Inherited Traits

Inherited Traits: A child may inherit certain characteristics which are similar to its parents.

Rules for the Inheritance of Traits – Mendel’s Contributions

Each trait of a child can be influenced by both paternal and maternal DNA.

Mendel worked out the main rules of such inheritance.

Mendel used a number of contrasting visible characters of garden peas –

  1. Round/wrinkled seeds,
  2. Tall/short plants,
  3. White/violet flowers and so on.

He took pea plants with different characteristics – a tall plant and a short plant, produced progeny from them, and calculated the percentages of tall or short progeny.

In the first place, – no ‘medium-height’ plants were observed. All plants were tall. Thus only one of the parental traits was seen.

But, the second-generation, or F2, progeny of the F1 tall plants were not all tall. One quarter of them were short. This indicates that both the tallness and shortness traits were inherited in the F1 plants, but only the tallness trait was expressed. So, two copies of the trait are inherited in each sexually reproducing organism. These two may be identical, or may be different, depending on the parentage.

Don’t Miss : Control and Coordination

Note that a single copy of ‘T’ is enough to make the plant tall, while both copies have to be ‘t’ for the plant to be short. Traits like ‘T’ are called dominant traits. Those that behave like ‘t’ are called recessive traits.

Different traits are independently inherited. For. eg. tall/short trait and the round seed/wrinkled seed traits.

Mendel's experiment : Heredity and Evolution Class 10 Notes
Mendel’s experiment

How do these Traits get Expressed?

A section of DNA that provides information for one protein is called the gene for that protein. These genes control characteristics, or traits.

Gene set is present, not as a single long thread of DNA, but as separate independent pieces each called a chromosome. Thus, each cell will have two copies of each chromosome, one each from the male and female parents. When two germ cells combine, they will restore the normal number of chromosomes in the progeny. This ensures stability of the DNA of the species.

Sex Determination

Some animals rely entirely on environmental cues. Thus, in some animals, the temperature at which fertilised eggs are kept determines whether the animals developing in the eggs will be male or female.

In human beings, the sex of the individual is largely genetically determined. The genes inherited from our parents decide whether we will be boys or girls. Most human chromosomes have a maternal and a paternal copy, and we have 22 such pairs. There is still one pair, called the sex chromosomes, is odd in not always being a perfect pair. Women have a perfect pair of sex chromosomes, both called X. But men have a mismatched pair in which one is a normal-sized X while the other is a short one called Y.

Thus women are XX, while men are XY.

All children will inherit an X chromosome from their mother regardless of whether they are boys or girls.

Thus, the sex of the children will be determined by what they inherit from their father.

Sex Determination : Heredity and Evolution Class 10 Notes
Sex Determination

Evolution

Genes control traits, and the frequency of certain genes in a population changes over generations. This is known as evolution.

Acquired and Inherited Traits

Change in non-reproductive tissues that cannot be passed on to the DNA of the germ cells are called acquired traits.

For example. obesity, skinny because of starvation, etc.

Change in reproductive tissues that can be passed on to the DNA of the germ cells are called inherited traits.

For example. height, eye colour, skin colour, etc.

Speciation

Formation of new species over time from an already prevailing species is known as speciation. Speciation results when one species is divided into two different sub species due to very less interaction among the two groups.

Evolution and Classification

Characteristics are details of appearance or behaviour; in other words, a particular form or a particular function. We have four limbs. Thus having four limbs is a characteristic of human beings.

We can build up small groups of species with recent common ancestors, then super-groups of these groups with more distant common ancestors, and so on. This process of forming groups based on characteristics is called Classification.

Tracing Evolutionary Relationships

Homologous characteristics: Characteristics in different organisms that are similar because they are inherited from a common ancestor are known as homologous characteristics.

For example. Mammals have four limbs, so do birds, reptiles and amphibians.

Analogous characteristics: Sometimes some characteristics might look similar because they have a common use, but their origins might not be common. These type of characteristics are called analogous.

For example: Wings of bats and wings of birds.

Evolutionary Relationships : Heredity and Evolution Class 10 Notes
Evolutionary Relationships

Fossils

If a dead animal might get caught in hot mud, for example, it will not decompose quickly, and the mud will eventually harden and retain the impression of the body parts of the animal, such preserved traces of living organisms are called fossils.

Evolution should not be equated with ‘progress’

Evolution might result into better adaptation of an organism. But it is not necessarily always a better adaptation. Thus it might not be a progress. There is no real ‘progress’ in the idea of evolution.

Evolution is simply the generation of diversity and the shaping of the diversity by
environmental selection. Many of the older and simpler designs also still survive. For example. bacteria and cockroaches.

Just like that all humans are a single species. Regardless of where we have lived for the past few thousand years, we all come from Africa. The earliest members of the human species, Homo sapiens, can be traced there.

Heredity and Evolution Class 10 Notes : Exercises

Q. 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
(a) TTWW
(b) TTww
(c) TtWW
(d) TtWw

Ans. (c) TtWW

Q. An example of homologous organs is
(a) our arm and a dog’s fore-leg.
(b) our teeth and an elephant’s tusks.
(c) potato and runners of grass.
(d) all of the above.

Ans. (b) our teeth and an elephant’s tusks.

Q. In evolutionary terms, we have more in common with
(a) a Chinese school-boy.
(b) a chimpanzee.
(c) a spider.
(d) a bacterium.

Ans. (a) a Chinese school-boy.

Q. 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?

Ans. It cannot be concluded whether light eye colour is dominant or recessive.

Q. How are the areas of study – evolution and classification – interlinked?

Ans. Two species are more closely related if they have more characteristics in common. And if two species are more closely related, it will mean that they have a more recent ancestor.

In evolution also if the two different species have more characteristics similar that will mean that they might have had a common ancestor.

Heredity and Evolution Class 10 Notes : More Questions

Q. Explain the terms analogous and homologous organs with examples.

Ans. Homologous characteristics: Characteristics in different organisms that are similar because they are inherited from a common ancestor are known as homologous characteristics.

For example. Mammals have four limbs, so do birds, reptiles and amphibians.

Q. Analogous characteristics: Sometimes some characteristics might look similar because they have a common use, but their origins might not be common. These type of characteristics are called analogous.

For example: Wings of bats and wings of birds.

Q. Explain the importance of fossils in deciding evolutionary relationships.

Ans. If a dead animal might get caught in hot mud, for example, it will not decompose quickly, and the mud will eventually harden and retain the impression of the body parts of the animal, such preserved traces of living organisms are called fossils.

These fossils provide evidence of animals which are extinct too. Those animals help us link today’s animals and let us draw the evolutionary chart.

This way fossils are important in deciding evolutionary relationships.

Q. What evidence do we have for the origin of life from inanimate matter?

Ans. J.B.S. Haldane, a British scientist, suggested in 1929 that life must have developed from the simple inorganic molecules which were present on earth soon after it was formed. He speculated that the conditions on earth at that time, which were far from the conditions we see today, could have given rise to more complex organic molecules that were necessary for life. The first primitive organisms would arise from further chemical synthesis.

Heredity and Evolution Class 10 Notes : Think It Yourself

Q. 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?

Ans. A section of DNA that provides information for one protein is called the gene for that protein. These genes control characteristics, or traits.

Gene set is present, not as a single long thread of DNA, but as separate independent pieces each called a chromosome. Thus, each cell will have two copies of each chromosome, one each from the male and female parents. When two germ cells combine, they will restore the normal number of chromosomes in the progeny. This ensures stability of the DNA of the species.

These different sets of genes arises more viable variations than asexual reproduction.

This helps in bringing more stable variations which helps the organism in adapting to its surrounding and it eliminates the weak genes.

Heredity and Evolution Class 10 Notes : Test Yourself

Q. How is the equal genetic contribution of male and female parents ensured in the progeny?

Ans. Gene set is present, not as a single long thread of DNA, but as separate independent pieces each called a chromosome. Thus, each cell will have two copies of each chromosome, one each from the male and female parents. When two germ cells combine, they will restore the normal number of chromosomes in the progeny. This ensures stability of the DNA of the species.

Now in human beings, the sex of the individual is largely genetically determined. The genes inherited from our parents decide whether we will be boys or girls. Most human chromosomes have a maternal and a paternal copy, and we have 22 such pairs. There is still one pair, called the sex chromosomes, is odd in not always being a perfect pair. Women have a perfect pair of sex chromosomes, both called X. But men have a mismatched pair in which one is a normal-sized X while the other is a short one called Y.

Thus women are XX, while men are XY.

This is how the equal genetic contribution of male and female parents ensured in the progeny.

Q. 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?

Ans. Yes, I agree withthis statement the different sets of genes arises more viable variations than asexual reproduction.

This helps in bringing more stable variations which helps the organism in adapting to its surrounding and it eliminates the weak genes.

Therefor only variations that confer an advantage to an individual organism will survive in a population.

Heredity and Evolution Class 10 Notes : Conclusion

Heredity and Evolution Class 10 Notes. The chapter Heredity and Evolution is a very important chapter. Here you have learnt about evolution and heredity of species. You have learnt about analogous and homologous organs which provide an important basis on evolutionary chart. We also got to know about fossils.

This chapter is important as this forms the basics to more important chapters on the same topic in the higher classes.

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