Willer Academy

Class 10 Biology - Heredity and Evolution

Lectures

3

Key Topics

12

Activities

7

Homework

9

Introduction to Heredity & Mendel's Laws

Learning Objectives

Define heredity and variation

Understand Gregor Mendel's contributions to genetics

Explain key genetic terms: genes, alleles, traits

Analyze Mendel's monohybrid cross

Heredity vs. Variation

Heredity: Transmission of traits from parents to offspring

Example: A child inherits eye color from parents

Variation: Differences in traits among individuals

Example: Siblings have different heights despite same parents

Why Study Heredity?

• Explains continuity of life
• Understanding of biodiversity
• Key to evolutionary mechanisms

Gregor Mendel: Father of Genetics

Background: Austrian monk (1822-1884) who experimented with pea plants

Why Pea Plants?

• Easy to grow, short life cycle
• Clear contrasting traits
• Cross-pollination controllable

Traits studied: Plant height, seed color, flower position

Genetic Terminology

Gene: Unit of heredity (e.g., gene for plant height)

Allele: Variant form of a gene (T for tall, t for short)

Dominant Allele: Expressed with one copy (T)

Recessive Allele: Needs two copies to express (t)

Genotype: Genetic makeup (TT, Tt, tt)

Phenotype: Physical expression (tall or short)

Mendel's Monohybrid Cross

Experiment: Crossed purebred tall (TT) and purebred short (tt) pea plants

F1 Generation: All offspring tall (Tt)

Observation: Dominant trait masked recessive trait

F2 Generation: Self-pollinated F1 plants (Tt × Tt)

Punnett Square:

	T	t
T	TT (tall)	Tt (tall)
t	Tt (tall)	tt (short)

Results:

Genotypic ratio: 1 TT : 2 Tt : 1 tt

Phenotypic ratio: 3 tall : 1 short

Mendel's Laws

Law of Dominance: In heterozygous pair, dominant allele expresses itself

Law of Segregation: Alleles segregate during gamete formation

Activities & Visual Aids

Punnett Square Practice

Cross homozygous yellow (YY) and green (yy) pea plants. Predict F1 and F2 ratios.

Heredity Flowchart

Visualize the inheritance pattern from P generation to F2 generation.

Class Trait Survey

Record traits like tongue-rolling ability to observe variation in class.

Homework

1

Define: allele, genotype, phenotype with examples.

2

Cross a homozygous dominant (RR) red-flowered plant with a homozygous recessive (rr) white-flowered plant. Show F1 and F2 generations.

3

Reflect: Why did recessive traits disappear in F1 but reappear in F2?

Dihybrid Cross, Sex Determination & Evolution Basics

Learning Objectives

Apply Mendel's dihybrid cross and Law of Independent Assortment

Explain sex determination in humans

Differentiate between inherited and acquired traits

Introduce evolution and fossil evidence

Mendel's Dihybrid Cross

Experiment: Crossed plants with two traits (round-yellow × wrinkled-green)

P Generation: RRYY × rryy

F1 Generation: All RrYy (round-yellow)

F2 Generation: Self-pollinated RrYy × RrYy

Phenotypic Ratio: 9:3:3:1

Law of Independent Assortment: Genes for different traits segregate independently during gamete formation.

Sex Determination in Humans

Chromosomes:

• Autosomes: 22 pairs (non-sex traits)
• Sex Chromosomes:
  • Females: XX
  • Males: XY

Parent	Gametes	Offspring
Father	X or Y sperm	XX (Female) XY (Male)
Mother	X egg	XX (Female) XY (Male)

Key Insight: Sex of child determined by father's sperm

Inherited vs. Acquired Traits

Inherited Traits	Acquired Traits
Passed via genes (DNA)	Gained during lifetime
Example: Blood group	Example: Muscle strength
Evolutionary significance	Not passed to offspring

Evolution: The Basics

Definition: Gradual change in species over generations due to genetic variations

Fossils: Time Capsules

Evidence of extinct organisms (e.g., dinosaur bones)

Dating Methods:

• Relative: Rock layer depth
• Absolute: Radioactive carbon dating

Archaeopteryx: Fossil showing transition between reptiles and birds

Activities & Visual Aids

Dihybrid Cross Challenge

Cross: TtGg (tall, green pod) × TtGg. Predict F2 phenotypic ratio.

Karyotype Activity

Identify XX/XY chromosomes from printed images.

Fossil Timeline

Arrange fossil cards from oldest to youngest.

Homework

1

Solve: Cross AaBb (round-yellow) × aabb (wrinkled-green). Show F1 & F2 ratios.

2

Debate: "Acquired traits can drive evolution." (Lamarck vs. Darwin)

3

Research: One Indian fossil site and its significance.

Natural Selection, Speciation & Human Evolution

Learning Objectives

Explain Darwin's theory of natural selection

Describe speciation and genetic drift

Trace human evolutionary stages

Analyze evidence for evolution

Darwin's Natural Selection

Key Steps:

1. Overproduction: Species produce more offspring than can survive
2. Competition: Struggle for resources
3. Variation: Genetic differences in populations
4. Adaptation: Beneficial traits enhance survival
5. Survival of the Fittest: Adapted individuals reproduce
6. Speciation: Accumulated changes create new species

Peppered Moths:

Pre-1800s: Light moths camouflaged on lichen-covered trees

Post-Industrial Revolution: Soot darkened trees → dark moths survived better

Speciation

Definition: Evolution of new species from existing ones

Causes:

• Geographical Isolation: Physical barriers split populations
Example: Grand Canyon squirrels evolved into distinct species
• Genetic Drift: Random allele changes in small populations
Example: Amish community's high polydactyly rate

Outcome: Reproductive isolation (inability to interbreed)

Human Evolution

Species	Time	Features
Australopithecus	4 mya	Bipedal, small brain
Homo habilis	2.4 mya	Stone tools, 600cc brain
Homo erectus	1.8 mya	Fire use, migration
Homo sapiens	0.3 mya	Art, language, large brain

Key Insight: Brain size doubled in 2 million years

Evidence for Evolution

Homologous Organs: Same structure, different function

Example: Human arm, bat wing, whale flipper

Analogous Organs: Different structure, same function

Example: Bird wing vs. butterfly wing

Molecular Evidence:

• Humans-chimps: 98% DNA identical
• Shared "junk DNA" sequences

Activities & Visual Aids

Natural Selection Game

Use colored beans on cloth to simulate predator-prey dynamics.

Skull Cast Analysis

Compare Australopithecus vs. Homo sapiens skulls.

Concept Mapping

Create evolution concept maps showing relationships.

Homework

1

Label homologous structures in human, bird, and bat limbs.

2

Case Study: How antibiotic resistance proves natural selection.

3

Create timeline of human evolution using models.

"It is not the strongest species that survive, nor the most intelligent, but the ones most responsive to change." — Charles Darwin (adapted)

Willer Academy - Biology Chapter Notes | Heredity and Evolution

Class 10 | Prepared for Academic Excellence