1. Heredity, Genes, and Genetics
➤ Heredity
= Heredity is the transmission of traits (characters) from parents to offspring.
➤ Genes
= A gene is the basic unit of heredity made up of DNA, which determines specific characteristics.
- Located on chromosomes
- Control traits like height, eye color, etc.
➤ Genetics
= Genetics is the branch of science that studies heredity and variation.
2. Cell Division
= Cell division is the process by which a parent cell divides into two or more daughter cells.
➤ Somatic Cells vs. Gametogenic Cells
| Feature | Somatic Cells | Gametogenic Cells |
| Also called | Body cells | Sex cells (sperm/egg) |
| Chromosomes | Diploid (2n) | Haploid (n) |
| Cell division | Mitosis | Meiosis |
| Role | Growth and repair | Reproduction |
3. Types of Cell Division
Mitosis (Equational Cell Division)
- Occurs in somatic cells
- Produces two identical daughter cells
- Each daughter cell has the same number of chromosomes as the parent cell (2n → 2n)
Main Features of Mitosis
- One division only
- No change in chromosome number
- Four phases: Prophase, Metaphase, Anaphase, Telophase
Significance of Mitosis
- Growth of organisms
- Repair and regeneration of tissues
- Asexual reproduction
Meiosis (Reduction Division)
- Occurs in gametogenic cells
- Produces four haploid daughter cells (2n → n)
- Involves two successive divisions
Two Main Stages of Meiosis:
- Meiosis I – Homologous chromosomes separate
- Meiosis II – Sister chromatids separate
Main Features
- Chromosome number is halved
- Introduces genetic variation
- Four non-identical cells produced
Significance of Meiosis
- Maintains chromosome number in species
- Creates genetic diversity through recombination
4. DNA (Deoxyribonucleic Acid)
Structure of DNA
- Double helix (like a twisted ladder)
- Made of nucleotides: phosphate, sugar (deoxyribose), nitrogen base
- Bases: Adenine (A), Thymine (T), Cytosine (C), Guanine (G)
🔁 A pairs with T, C pairs with G
Functions of DNA
- Stores genetic information
- Directs protein synthesis
- Passes traits to the next generation
5. RNA (Ribonucleic Acid)
Structure of RNA
- Single-stranded
- Sugar: Ribose
- Bases: A, Uracil (U), C, G
(No thymine)
Functions of RNA
- Helps in protein synthesis (mRNA, tRNA, rRNA)
- Carries messages from DNA to ribosomes
6. Chromosomes
Structure of Chromosomes
- Thread-like structures made of DNA and proteins
- Visible during cell division
Types of Chromosomes
- Autosomes – Body chromosomes (in humans: 22 pairs)
- Sex chromosomes – Determine sex (1 pair)
Number of Chromosomes
- Humans: 46 chromosomes (23 pairs)
- 44 autosomes
- 2 sex chromosomes (XX in females, XY in males)
7. Sex Determination
- Determined by sex chromosomes
- Male: XY, Female: XX
- Male sperm determines the sex of the baby
🧠 Mnemonic: “XY means a guy”
8. Mendelism and Genetic Technology
Gregor Mendel’s Work
- Father of Genetics
- Conducted experiments on pea plants
Mendel’s Material:
- Garden pea (Pisum sativum)
Why Pea Plants?
- Short life cycle
- Easily distinguishable traits
- Can self- or cross-pollinate
- Easy to grow and maintain
Dominant and Recessive Traits
| Type | Expressed When | Example |
| Dominant | At least one dominant allele present | Tall (T) |
| Recessive | Only when both alleles are recessive | Dwarf (tt) |
Genotype vs. Phenotype
| Term | Meaning | Example |
| Genotype | Genetic makeup | TT, Tt, tt |
| Phenotype | Physical appearance | Tall or Dwarf |
Monohybrid Cross
- Cross between parents with one pair of contrasting traits
e.g., Tall (TT) × Dwarf (tt)
Dihybrid Cross
- Cross involving two pairs of contrasting traits
e.g., Round Yellow × Wrinkled Green seeds
Mendel’s Laws
- Law of Dominance
Dominant allele masks the effect of a recessive allele. - Law of Segregation
Alleles segregate during gamete formation and reunite during fertilization.
9. Introduction to Genetic Technology
Definition
= Genetic technology involves manipulating genes to improve or modify organisms.
Methods:
- DNA testing
- Genetic engineering
- Gene therapy
- Recombinant DNA techniques
Advantages of Genetic Technology
- Cure genetic diseases
- Improve crop and animal breeds
- Solve paternity and crime investigations
- Produce insulin, vaccines, etc.
10. Role of DNA Testing
- Paternity testing
- Crime investigations
- Identification of genetic diseases
- Research in ancestry and evolution
11. Selective Breeding
Definition:
= Breeding organisms with desirable traits to produce better offspring.
Advantages:
- Improves yield
- Enhances resistance to diseases
- Better quality meat, milk, crops
Disadvantages:
- Reduces genetic variation
- Risk of inherited diseases
12. Methods of Selective Breeding
Inbreeding
- Mating between closely related individuals
✅ Fixes traits
❌ Can increase genetic disorders
Line Breeding
- Inbreeding with less close relatives
- Maintains useful traits with less risk
Self-Pollination
- Fertilization within the same flower
✅ Maintains purity
❌ No variation
Cross-Pollination
- Fertilization between different flowers
✅ More variation
❌ Risk of unwanted traits
13. Cross Breeding
Advantages
- Increases genetic variation
- Improves productivity and resistance
Disadvantages
- Unpredictable traits
- May lose some desired traits
Examples of Cross-Bred Organisms
- Mule (Donkey × Horse)
- Triticale (Wheat × Rye)
14. Artificial Insemination (AI)
Definition
Introducing sperm into the female’s uterus without natural mating.
Advantages:
- Controlled breeding
- Disease-free sperm
- High-quality offspring
Disadvantages:
- Costly and technical
- Not always successful
15. In-Vitro Fertilization (IVF)
- Fertilization outside the body, in a lab
- Egg and sperm are combined in a test tube
About Louise Brown
- First baby born through IVF in 1978, UK
Procedure:
- Eggs and sperms collected
- Fertilization done in a lab
- Embryo inserted into uterus
Advantages
- Helps infertile couples
- Increases chances of pregnancy
Disadvantages
- Expensive
- Ethical issues
- May lead to multiple births
🌟 Interesting Facts about Heredity
- Humans share about 98.8% DNA with chimpanzees!
- One strand of DNA is 2 meters long when uncoiled.
- Gregor Mendel used over 28,000 pea plants in his experiments.
- There are about 20,000–25,000 genes in the human genome.
🧠 Quick Revision Summary
- Heredity passes traits; genes carry information
- Mitosis (growth), Meiosis (reproduction)
- DNA stores info, RNA helps make proteins
- Chromosomes: 46 in humans, determine traits & sex
- Mendel discovered inheritance laws via pea plants
- Genetic tech helps improve organisms
- Selective breeding, AI, IVF help enhance reproduction
❌ Common Mistakes Students Make
🚫 Confusing mitosis and meiosis
🚫 Assuming both parents decide baby’s sex (only sperm decides!)
🚫 Mixing genotype with phenotype
🚫 Forgetting function of royal jelly
🚫 Assuming artificial insemination and IVF are the same
also learn :- chapter 1 , chapter 2 , chapter 3 , chapter 4 , chapter 5
