Ch 09: Heredity & Evolution | Exam Fusion Prep

🧬 Genetics — Introduction

Gregor Johann Mendel

Father of Genetics

Pisum sativum

Garden pea (experiment plant)

7 pairs

Contrasting characters studied

Heredity = Transmission of traits from parent to offspring
Genetics = Study of genetic traits and their inheritance
Mendel studied 7 pairs of contrasting characters in garden pea
Tall / Dwarf | Round / Wrinkled seed | Yellow / Green seed | Purple / White flower etc.

📋 Mendel's Three Laws

1. Law of Dominance

Each trait controlled by a pair of factors/genes
One allele is dominant, other is recessive

Dominant	Recessive
Tall	Dwarf
Round seed	Wrinkled seed
Yellow seed	Green seed
Purple flower	White flower

2. Law of Segregation

During gametogenesis, allelic genes separate from each other
Each goes into different gametes
Also called "Law of Purity of Gametes"

3. Law of Independent Assortment

Inheritance of one trait does NOT affect inheritance of another trait
Genes assort independently during gamete formation

⚠ Exam Trap

Law of Segregation = "Purity of gametes". Law of Independent Assortment = Dihybrid cross se derived. Monohybrid cross = Law 1 & 2. Dihybrid = Law 3.

🔬 Monohybrid Cross

P generation: TT (Tall) × tt (Dwarf)
F1 generation: Tt (Hybrid Tall) — all tall
F1 self-pollination: Tt × Tt

	T	t
T	TT (Tall)	Tt (Tall)
t	Tt (Tall)	tt (Dwarf)

3 : 1

Phenotype ratio (Tall : Dwarf)

1 : 2 : 1

Genotype ratio (TT : Tt : tt)

🔬 Dihybrid Cross

P generation: RRYY (Round Yellow) × rryy (Wrinkled Green)
F1 generation: RrYy (Hybrid Round Yellow)
F1 gametes: RY, Ry, rY, ry × RY, Ry, rY, ry

	RY	Ry	rY	ry
RY	RRYY round yellow	RRYy round yellow	RrYY round yellow	RrYy round yellow
Ry	RRYy round yellow	RRyy round green	RrYy round yellow	Rryy round green
rY	RrYY round yellow	RrYy round yellow	rrYY wrinkled yellow	rrYy wrinkled yellow
ry	RrYy round yellow	Rryy round green	rrYy wrinkled yellow	rryy wrinkled green

9 : 3 : 3 : 1

Phenotype ratio (F2)

Round Yellow : Round Green : Wrinkled Yellow : Wrinkled Green

9 : 3 : 3 : 1

⚠ Exam Trap

Monohybrid F2 phenotype = 3:1. Dihybrid F2 phenotype = 9:3:3:1. Monohybrid genotype = 1:2:1. BbEe × BbEe mein BBEE probability = 1/16.

🧪 Chromosomal Theory of Inheritance

Chromosomal Theory

Given by Sutton and Boveri
Experimental verification: T.H. Morgan (fruit fly / Drosophila)
Genes present in pairs on homologous chromosomes
Chromosomes = carriers of genes

Gene Theory

Given by Thomas Hunt Morgan
Genes in linear order on chromosomes — like beads
Gene = physical unit = functional segment of DNA

🔬 DNA — Key Facts

Genetic material = Nucleic acid
Discoverer of nucleic acid: Friedrich Miescher (1869)
DNA as genetic material confirmed: Hershey & Chase (1952)
Double-stranded structure: Watson & Crick (1953)
Nucleotide = Nucleoside (Nitrogenous base + Deoxyribose sugar) + Phosphate (PO₄³⁻)

Nitrogenous Bases

Purines: Adenine (A) + Guanine (G)
Pyrimidines: Thymine (T) + Cytosine (C)
Base pairing: A–T and G–C

RNA vs DNA

RNA = Usually single-stranded
Sugar: Ribose (not deoxyribose)
Uracil (U) replaces Thymine (T)
Types: rRNA 80%, tRNA 10–15%, mRNA 3–5%

Gene expression flow:DNA → (Replication) → DNA → (Transcription) → mRNA → (Translation) → Protein

⚠ Exam Trap

Watson & Crick = Double helix model (1953). Hershey & Chase = Proved DNA is genetic material (1952). Miescher = Discovered nucleic acid (1869). Teen different scientists, teen different facts!

RNA mein Thymine nahi hoti — Uracil hoti hai. Honeybees: Male = Haploid, Female = Diploid.

🏥 Genetic Diseases — Complete Table

Disease	Type / Cause	Chromosomes	Key Symptoms / Effects
Haemophilia	X-linked recessive gene; Female carrier = XʰX	Sex chromosome	Blood does not clot — excessive bleeding. Haemophilia-A (Factor VIII deficiency), Haemophilia-B (Factor IX deficiency)
Colour Blindness (Daltonism)	X-linked recessive gene	Sex chromosome	Cannot distinguish between green and red colour
Sickle-cell Anaemia	Mutation in β-chain of Haemoglobin gene	Chromosome 11	Valine replaces Glutamic acid at 6th position → RBC become sickle-shaped → transport less O₂
Down's Syndrome	Trisomy of chromosome 21	Total = 47	Flat face, broad hands (palm crease), broad forehead, short & swollen fingers, thick tongue, rough skin, congenital heart disease, male impotent
Turner's Syndrome	Absence of one X chromosome (44 + X0)	Total = 45	Underdeveloped ovaries, infertility, short stature, webbed neck, absent menstrual cycle, underdeveloped breast
Klinefelter's Syndrome	Trisomy of X chromosome (44 + XXY)	Total = 47	Tall height, small testes, underdeveloped breasts, mentally retarded, impotent, Gynecomastia (both male & female characteristics)

⚠ Exam Trap

Down's = Trisomy 21, total 47 chromosomes. Turner's = 44+X0, total 45 (females). Klinefelter's = 44+XXY, total 47 (males). Haemophilia = X-linked, only females are carriers. Sickle cell = chromosome 11.

⚡ Quick Recall

Haemophilia-A = Factor VIII deficiency | Haemophilia-B = Factor IX deficiency. Colour blindness also X-linked — males more affected (they have only one X).

🦴 Biological Evolution

Development of complex organisms from simple and primitive life forms
Also called "Descent with modification"

📋 Evidences of Evolution

(i) Fossils

Remains of dead organisms preserved in primitive rocks of earth's crust
Age determination methods:
C¹⁴ Dating
U-Pb Dating
K-Ar Dating

(ii) Comparative Morphology & Anatomy

Type	Origin/Structure	Function	Example
Homologous organs	Similar origin & basic structure	Different functions	Forelimbs of vertebrates
Analogous organs	Different origin & basic structure	Similar functions	Wings of insects and birds
Vestigial organs	Functional in ancestors	Non-functional now	Vermiform appendix, Wisdom teeth, Coccyx (in humans)

(iii) Connecting Links

Organisms showing primitive + evolved traits together
Virus: Connecting link between Living and Non-living
Euglena: Between Animal and Plant
Archaeopteryx: Between Reptile and Bird

⚠ Exam Trap

Homologous = Same structure, DIFFERENT function (divergent evolution). Analogous = Different structure, SAME function (convergent evolution). Ye dono ulte lagte hain — confuse mat karna!

Archaeopteryx = Reptile + Bird connecting link. Euglena = Plant + Animal.

📚 Theories of Evolution

(i) Lamarckism

By: Jean Baptiste de Lamarck
Book: Philosophie Zoologique
Traits acquired from environmental effects are inherited
Organ becomes more developed if used frequently; disappears if not used
e.g. Giraffe's neck lengthened by stretching; snakes lost legs due to non-use

(ii) Darwinism / Natural Selection

By: Charles Darwin
Book: On the Origin of Species (1859)
Organisms overproduce, but numbers stay stable due to struggle for survival
"Survival of the Fittest"
New species over long period by natural selection

(iii) Mutation Theory

By: Hugo de Vries
Experiments on Evening Primrose
Mutations = Accidental and inherited changes in genome
New species arise by sudden mutations, not gradual changes

⚠ Exam Trap

Darwin's book = On the Origin of Species (1859). Lamarck's book = Philosophie Zoologique. Hugo de Vries = Mutation theory (Evening Primrose experiments). Darwin ne Lamarckism ko refute kiya!

⚡ Quick Recall

Lamarck → Learned traits inherited | Darwin → Descent, Natural selection | Hugo de Vries → Hop (sudden mutations)

🧬 Chapter 09 — Heredity & Evolution