📘Class 10 Science – Chapter: Heredity and Evolution Notes
🧬 Introduction to Heredity and Evolution
-
Heredity: Transmission of traits from parents to offspring.
-
Evolution: Gradual change in organisms over generations leading to the formation of new species.
🧬 Mendel’s Experiments
-
Gregor Mendel conducted experiments on pea plants.
-
Studied inheritance of traits.
Key Terms:
| Term | Meaning |
|---|---|
| Trait | Characteristic inherited (e.g., flower color, seed shape) |
| Gene | Unit of inheritance |
| Allele | Different forms of a gene |
| Dominant Trait | Expressed when at least one dominant allele is present |
| Recessive Trait | Expressed only in absence of dominant allele |
Mendel’s Laws:
-
Law of Dominance
-
Law of Segregation
-
Law of Independent Assortment
Example:
-
Cross between Tall (TT) and Dwarf (tt) pea plant:
Parent: TT × tt
F1 Gen: Tt (all tall)
F2 Gen: TT, Tt, Tt, tt (3 tall : 1 dwarf)
🧬 Sex Determination in Humans
-
Males: XY chromosomes; Females: XX chromosomes.
-
Sex of child depends on sperm contribution.
Table: Sex Determination
| Sperm (Father) | Egg (Mother) | Offspring’s Sex |
|---|---|---|
| X | X | Female (XX) |
| Y | X | Male (XY) |
Conclusion: Father is responsible for determining the sex of the child.
🔁 Evolution
-
Evolution explains origin and diversity of life.
-
Supported by fossils, comparative anatomy, and embryology.
Key Concepts:
| Concept | Explanation |
|---|---|
| Fossils | Remains of ancient organisms preserved in rocks |
| Homologous Organs | Same structure, different function (e.g., forelimbs of humans & bats) |
| Analogous Organs | Different structure, same function (e.g., wings of birds & insects) |
| Speciation | Formation of new species due to evolution |
Example: Archaeopteryx is a fossil showing features of both reptiles and birds.
🔄 Evolution and Classification
-
Evolution helps in classification based on common ancestors.
-
More similar characteristics → more closely related.
🔬 Acquired vs Inherited Traits
| Trait Type | Description | Example |
|---|---|---|
| Inherited Traits | Passed from parents via genes | Eye color, blood group |
| Acquired Traits | Gained during lifetime, not passed genetically | Learning to cycle, tattoos |
📊 Summary Table of Differences
| Concept | Inherited Trait | Acquired Trait |
|---|---|---|
| Transfer to offspring | Yes | No |
| Basis | Genetic | Environmental |
| Examples | Height, skin color | Injuries, language |