Heredity and Evolution Class 10 – Continuing our series for Class 10 Revision for CBSE board exams, we bring you a new chapter today i.e. Heredity and Evolution Class 10.
In previous years, questions of 2, 3 and 5 marks have been asked from this chapter. One important concept that is asked repeatedly is Mendel’s pea experiment, so make sure you study this thoroughly.
The concepts that are going to be discussed in this article are:
- Mendel’s pea experiment
- Sex determination
- Acquired and Inherited traits
- Speciation
- Homologous and Analogous organs
- Fossils
- Human evolution
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Let’s discuss each topic of Heredity and Evolution Class 10 one-by-one
Mendel’s pea experiment:
The study of inheritance or how some characters get inherited from parents to offspring has been baffling our scientists for long. What causes characters to be passed from one generation to another, why some characters are inherited and some not – were some questions that were to be answered. For this, Mendel started studying peas. He took pea plants with different characteristics – a tall plant and a short plant and started creating progenies out of them, and noticing if any characteristics have been inherited.
In this first generation, or F1 progeny he obtained all tall plants. However, the second-generation, or F2 progeny obtained by breeding first generation plants were not all tall. Instead, one quarter of them were short. Now what conclusions Mendel made regarding this, are explained in this video:
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Sex determination:
Let us now study how sex is determined in humans. This happens as:
Humans have a total of 23 pairs of chromosomes. 1 pair out of this – sex chromosomes – is different in males and females. Females have two X chromosomes in this pair, while males have an X and a Y.
Thus, a baby always receives X chromosome from the mother, while he/she can receive an X or a Y chromosome from father. Baby born with an XX combination is a girl, while an XY combination results in a boy.
Acquired and Inherited traits:
A trait or characteristic of an individual which is not inherited from parents but develops in response to the environment is called an acquired trait. For example, learning skating. It is a trait that a person acquires in his/her lifetime. he/she is not born with this trait, and thus cannot pass it onto the next generation.
Only those traits can be passed to the next generation in which changes have occurred in the genes or DNA of the organism. Such traits are called inherited traits. For example, colour of eyes, hair, etc
Speciation:
First we need to know what is ‘species’. A species is a population of organisms consisting of similar individuals which can breed together and produce an offspring. For example, all humans belong to the same species; but humans and dogs are different species. Scientists have seen that there are some factors that lead to formation of new species, a process known as speciation. These factors can be:
- Geographical isolation of a population of a certain species (such as by mountain ranges, river or sea)
- Genetic drift (caused by drastic changes in the frequencies of particular gene occurring by chance)
- Variations caused by natural selection)
Homologous and Analogous organs:
Various biological studies have told us that since their origin, living organisms have undergone changes in their organisation to evolve into new forms. Thus, we can say that more characteristics two species have in common, more closely they will be related.
One way of analysing how closely related two organisms are is by observing their organs.
Some organisms have the same structure of some organs, but use them for same or different purposes. Such organs are called homologous organs. For example, limbs of frog, lizard, human and bird, as you can see from the image:
Note that all these have different functions –
- Limbs of a man 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 are used for the same thing. Such organs are called analogous organs. For example, wings of a bat and a bird.
Fossils:
Preserved traces of living organisms are called fossils. Study of fossils is very important, as it provides evidence for evolution. But the interesting question is, how are fossils formed!?
Usually, when organisms die, their bodies will decompose and be lost. But every once in a while, the body or at least some parts may be in an environment that does not let it decompose completely
Human Evolution:
Excavating, time dating, etc have revealed a lot of information about human evolution. Scientists today know that all humans, irrespective of their colour, are a single species. Not only that, regardless of where we have lived for the past few thousand years, we all come from Africa. It is also not true that human beings evolved from chimpanzees. Rather, both human beings and chimpanzees have a common ancestor from a long time ago. That common ancestor is likely to have been neither human or chimpanzee.