NCERT Books for Class 10 Science Chapter 9

Topics in the Chapter

The topics discussed in this chapter are listed below-

1. Accumulation of Variation During Reproduction

2. Evolution

1. Acquired and Inherited Traits

3. Evolution and Classification

1. Evolution by Stages

2. Tracing Evolutionary Relationships

3. Fossils

4. Speciation

5. Evolution Should Not Be Equated With ‘Progress'

1. Human Evolution

6. Heredity

1. How do these Traits get Expressed?

2. Inherited Traits

3. Mendel’s Contributions

4. Sex Determination

Mind Map

Variation accumulation during Reproduction

• During reproduction, characters, features, and qualities are passed down from generation to generation.

• This inheritance supplies the next generation with both a shared fundamental body design and minor alterations.

• When this generation reproduces, the children will inherit both inherited and newly developed differences from the preceding generation.

• Variations in a population occur as a result of the accumulation of these differences from generation to generation.

• Different variations offer different benefits to the population, and the variation that offers the best chances of survival is passed down to the following generation.

Heredity

• The transmission of features from parent to offspring via genes in the chromosomes is referred to as heredity.

• Contributions of Mendel

• Mendel was the first scientist whose research led to the development of inheritance laws.

• He explored the transmission of features with two contrasting traits, such as round/wrinkled seeds, tall/short plants, white/violet flowers, and so on, in cross-hybridization tests of the garden pea plant (Pisum sativum).

Determination of sex

• Different animals employ various techniques to accomplish this:

• The temperature at which fertilised eggs are stored, for example, impacts the sex of developing creatures in the eggs. Crocodiles, turtles, and other animals have been observed to have it.

• Snails may alter their gender, suggesting that sex is not defined by genetics.

• Humans, for example, have a genetically defined sex.

Evolution

• It refers to the gradual change in population characteristics (plants and animals) over successive generations.

• Evolution is explained by errors in DNA copying during reproduction, mutations, and natural selection.

• Evolution creates biodiversity at every level of biological organisation, including species, people, molecules, and so on.

'Progress' Should Not Be Associated With Evolution

• Evolution is simply the generation and shaping of diversity through environmental selection.

• The only apparent progressive trend in evolution appears to be the formation of increasingly complex body forms throughout time. However, this does not imply that previous designs are ineffective.

• Bacteria, for example, live in the most inhospitable environments, such as hot springs, deep-sea thermal vents, and ice in Antarctica.

Human Evolution

• Tools have been employed to investigate human evolution, including excavating, time-dating, and examining fossils, determining DNA sequences, and so on.

• Regardless of skin colour or the human race, all people are a single species.

• Homo sapiens, the oldest members of the human species, may be traced back to Africa, implying that we are all descended from Africans.

• Some of our forefathers departed Africa a few hundred thousand years ago, while others remained.

• The migrants migrated gradually throughout the globe, from Africa to West Asia, then to Central Asia, Eurasia, South Asia, and East Asia.

• They traveled down the Indonesian and Philippine islands to Australia, then across the Bering land bridge to the Americas.