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ᒪEᗩᖇᑎIᑎG ᒍᑌᑎᑕTIOᑎ
CBSE
CLASS 10 SCIENCE
CHAPTER 9:HEREDITY AND EVOLUTION
NOTES
1. Heredity:
👉Heredity is the process by which traits or characteristics are passed from parents to offspring.
👉The unit of heredity is called a gene, which is a segment of DNA.
👉Genes are located on chromosomes, and humans have 23 pairs of chromosomes.
👉The different forms of a gene are called alleles.
2. Mendel's Laws of Inheritance:
👉Gregor Mendel, an Austrian monk, is known as the father of genetics.
👉Mendel formulated three laws of inheritance based on his experiments with pea plants.
👉Law of Dominance: In a pair of alleles, one allele dominates or masks the effect of the other.
👉Law of Segregation: During gamete formation, the alleles segregate or separate from each other.
👉Law of Independent Assortment: The segregation of alleles for one gene occurs independently of the segregation of alleles for another gene.
3. Sex Determination:
👉In humans, the sex of an individual is determined by the sex chromosomes.
👉Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).
👉The sex of a child is determined by the father because he can contribute either an X or Y chromosome.
4. Evolution:
👉Evolution is the gradual change in the inherited characteristics of a population over successive generations.
👉Charles Darwin proposed the theory of evolution through natural selection.
👉Natural selection is the process by which organisms with favorable traits survive and reproduce more successfully than those with less favorable traits.
👉The factors that lead to the survival of certain traits include variations, competition, survival of the fittest, and inheritance of favorable traits.
5. Speciation:
👉Speciation is the process by which new species arise from existing ones.
👉It occurs due to isolation and accumulation of differences between populations.
👉The two types of isolation are geographical isolation (physical barriers) and reproductive isolation (barriers to reproduction).
👉Speciation can lead to the formation of new species over long periods of time.
6. Fossils and Evolution:
👉Fossils are the preserved remains or traces of ancient organisms.
👉Fossils provide evidence of the existence of organisms that lived in the past and how they have evolved over time.
👉Transitional fossils show intermediate forms between different groups of organisms, supporting the theory of evolution.
7. Evolution and Human Evolution:
👉Humans have evolved from primates, specifically from a common ancestor with apes.
👉The study of human evolution is based on fossil records, comparative anatomy, embryology, and molecular evidence.
👉Homo sapiens (modern humans) have distinctive features like an upright posture, larger brain size, and the ability to use tools.
⭐These are some key points from Chapter 9: Heredity and Evolution. Make sure to refer to your textbook and class notes for more detailed information on the topic.
