🔥 Chapter 8: Heredity and Evolution

🎯 Class 10 Science Best Notes (With Hindi Explanation)

🧬 1. What is Heredity?

The passing of traits from parents to offspring is called heredity.
👉 Hindi: Heredity ka matlab hai maa-baap ke gun santaan tak jaana.

📘 2. Mendel’s Experiment

👨‍🔬 Gregor Mendel did experiments on pea plants.
He is known as Father of Genetics.

🔹 Traits studied:

• Tall/Short plant
  
  

• Round/Wrinkled seeds
  
  

• Yellow/Green seeds
  
  

🔹 Important Law:
Law of Dominance: Dominant trait always expresses itself in F1 generation.

👉 Hindi: Mendel ne pea plant par prayog kiya aur bataya ki kuch traits (gun) dominant hote hain.

🌱 3. Important Terms

• Gene: Unit of inheritance
  
  

• Allele: Different forms of a gene
  
  

• Dominant Trait: Strong gene (e.g., tall)
  
  

• Recessive Trait: Weak gene (e.g., short)
  
  

• Genotype: Genetic makeup (TT, Tt, tt)
  
  

• Phenotype: Physical appearance (Tall/Short)
  
  

🔁 4. Monohybrid Cross (1 Trait)

🔹 Cross between tall (TT) and short (tt) plants

• F1 → All Tall (Tt)
  
  

• F2 → 3 Tall : 1 Short
  👉 Ratio = 3:1
  👉 Hindi: Ek gun ke liye kriya – jaise height – isse monohybrid cross kehte hain.
  
  

🧬 5. Variation

Differences between individuals of same species
🔹 Types:

• Inherited Variation: From parents
  
  

• Acquired Variation: Due to environment
  
  

👉 Hindi: Har vyakti ek jaise nahi hote, yehi variation hai.

🧫 6. Sex Determination in Humans

🔹 Human chromosomes = 23 pairs
🔹 22 pairs = autosomes
🔹 1 pair = sex chromosomes (XX in female, XY in male)
👉 Male decides baby’s gender
👉 Hindi: Bacche ka gender pita decide karta hai (X ya Y dekar)

🦕 7. Evolution

Gradual change in living organisms over time
🔹 Proposed by Charles Darwin
👉 Hindi: Jeevon mein dheere-dheere badlav ko evolution kehte hain.

🐦 8. Speciation

Formation of new species due to:

• Genetic variation
  
  

• Natural selection
  
  

• Isolation
  
  

📊 9. Tracing Evolution

🔹 Fossils (e.g., Archaeopteryx)
🔹 Homologous Organs – Same structure, different function
👉 Example: Forelimbs of humans and bats
🔹 Analogous Organs – Different structure, same function
👉 Example: Wings of bat and insect

🔬 10. Human Evolution

🔹 Humans evolved from primates (apes)
🔹 Evidence from fossils, DNA, and tools used

📘 Important Questions for Practice — With Answers

✅ 1 Mark Questions

1. Who is known as the father of genetics?
   👉 Gregor Mendel
   
   

2. What is the sex chromosome in females?
   👉 XX
   
   

3. Give one example of an analogous organ.
   👉 Wings of birds and insects
   
   

✅ 2 Mark Questions

1. What do you mean by inherited and acquired traits?
   👉
   
   

• Inherited: Passed from parents (e.g., eye color)
  
  

• Acquired: Gained from environment (e.g., scars)
  
  

2. Why are traits acquired during the lifetime not inherited?
   👉 Because they don’t affect genes of reproductive cells.
   
   

✅ 3 Mark Questions

1. Explain Mendel’s monohybrid cross with example.
   👉 Tall (TT) × Short (tt)
   F1: All Tall (Tt)
   F2: 3 Tall : 1 Short
   This proves dominance and segregation of genes.
   
   

2. Difference between homologous and analogous organs:
   | Homologous | Analogous | |-----------------------------|-------------------------------| | Same structure | Different structure | | Different function | Same function | | Example: human arm & bat wing | Example: bat wing & insect wing |
   
   

✅ 5 Mark Questions

1. Describe sex determination in humans with diagram.
   👉
   
   

• Males: XY
  
  

• Females: XX
  
  

• If sperm gives X → Girl (XX)
  
  

• If sperm gives Y → Boy (XY)
  (Diagram banana zaroori hai)
  
  

2. What is evolution? Explain with fossil and organ evidence.
   👉 Evolution is slow change in organisms.
   Evidence:
   
   

• Fossils (e.g., Archaeopteryx)
  
  

• Homologous organs: Common ancestry
  
  

• Analogous organs: Adaptation to environment