Summary of Class 10 Science Chapter 9: Heredity and Evolution
Heredity and evolution are central concepts in biology that explain how traits are passed from one generation to the next and how species change over time. Chapter 9 explores the fundamental principles of heredity, the process of inheritance, and the theory of evolution, providing insights into how genetic variations lead to the diversity of life.
What is Heredity?
Heredity is the process by which traits or characteristics are passed from parents to their offspring through genes. This process ensures that offspring inherit a combination of traits from both parents, contributing to their genetic makeup.
Genes and Chromosomes
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Genes: Genes are segments of DNA that carry genetic information. They are the basic units of heredity.
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Chromosomes: Chromosomes are structures made of DNA and proteins, located in the cell nucleus. Humans have 23 pairs of chromosomes, carrying thousands of genes.
(Caption: Chromosomes are made up of DNA and contain genes that carry hereditary information.)
1. Mendel’s Laws of Inheritance
Gregor Mendel, known as the father of genetics, conducted experiments on pea plants and formulated the basic laws of inheritance.
Mendel's Laws
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Law of Dominance: In a pair of alleles, one allele is dominant and the other is recessive. The dominant allele expresses its trait in the phenotype (physical appearance).
(Caption: Mendel’s Law of Dominance states that the dominant allele overpowers the recessive allele.) -
Law of Segregation: During the formation of gametes (sperm and egg), the two alleles for a trait separate, and each gamete receives one allele.
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Law of Independent Assortment: Alleles for different traits segregate independently of one another during gamete formation.
2. Sex Determination in Humans
In humans, sex is determined by the combination of sex chromosomes inherited from the parents.
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XX: Females have two X chromosomes.
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XY: Males have one X and one Y chromosome.
(Caption: The combination of sex chromosomes determines the gender of the offspring.)
The Y chromosome carries the gene for male characteristics, while the X chromosome contains genes for both male and female traits. The offspring’s sex is determined by the sperm cell that fertilizes the egg: if the sperm carries an X chromosome, the offspring will be female, and if it carries a Y chromosome, the offspring will be male.
3. Genetic Disorders
Genetic disorders are caused by abnormalities in the genes or chromosomes. These disorders can be inherited from one or both parents.
Types of Genetic Disorders
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Monohybrid Disorders: Caused by a mutation in a single gene. Examples include cystic fibrosis and sickle cell anemia.
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Chromosomal Disorders: Caused by abnormalities in the number or structure of chromosomes. Down syndrome is a common chromosomal disorder caused by an extra copy of chromosome 21.
(Caption: Genetic disorders can be inherited through mutations in genes or chromosomes.)
4. Evolution: The Process of Change
Evolution refers to the gradual change in the characteristics of a species over time. This process leads to the development of new species from existing ones.
Darwin’s Theory of Evolution
Charles Darwin proposed the theory of natural selection, which states that organisms with advantageous traits are more likely to survive and reproduce, passing on these traits to future generations.
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Survival of the Fittest: Organisms best adapted to their environment have higher chances of survival and reproduction.
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Variation: Variations (differences in traits) exist within a population and are inherited by offspring.
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Natural Selection: Over generations, favorable traits become more common in the population, leading to the evolution of new species.
(Caption: Darwin’s theory of evolution explains how species evolve over time through natural selection.)
Evidence for Evolution
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Fossils: Fossils provide evidence of organisms that lived millions of years ago, showing how life forms have changed over time.
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Comparative Anatomy: The study of similarities and differences in the anatomy of different species provides evidence for common ancestry.
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Embryology: Similarities in the development of embryos across species suggest common ancestry.
(Caption: Fossils provide evidence for the changes in organisms over time.)
5. Speciation: Formation of New Species
Speciation occurs when a population of organisms becomes so genetically distinct from the original population that it can no longer interbreed with it, leading to the formation of a new species.
Process of Speciation
- Isolation: A group of organisms is separated from the main population, often by geographical barriers.
- Genetic Divergence: Over time, the isolated group accumulates genetic changes.
- Reproductive Isolation: When the genetic differences become significant, the isolated group cannot reproduce with the original population.
6. Evolution and Human Beings
Humans have evolved over millions of years from a common ancestor with other primates. Evidence for human evolution comes from the study of fossils, genetic similarities, and anatomical features.
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Homo sapiens: Modern humans evolved from earlier hominids, such as Australopithecus and Homo habilis.
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Adaptation: Humans have adapted to diverse environments, and the development of complex tools, language, and culture has contributed to our success as a species.
(Caption: Human evolution shows the gradual development of human beings from early ancestors.)
Conclusion
Heredity and evolution are interconnected concepts that explain how traits are inherited and how species evolve over time. Mendel’s laws of inheritance lay the foundation for understanding genetic variation, while Darwin’s theory of evolution offers insight into how natural selection drives the process of change. Genetic disorders, speciation, and human evolution further illustrate the complexity of life on Earth.
Did You Know?
- Humans and chimpanzees share approximately 98% of their DNA, pointing to a common ancestor.
- The peppered moth in England evolved from light to dark coloration as a result of industrial pollution, an example of natural selection.
Image Sources
- Structure of chromosome: Pexels, Pixabay.
- Mendel’s law of dominance: Pixabay, Pexels.
- Sex determination: Unsplash, Pexels.
- Genetic disorders: Pixabay, Pexels.
- Darwin’s theory of evolution: Unsplash, Pixabay.
- Fossil evidence for evolution: Pixabay, Pexels.
- Human evolution: Pexels.
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