Chromosomes and DNA are the foundation of genetics and heredity. In this unit, students learn how genetic information is stored, copied, and transferred from parents to offspring. DNA carries the instructions for life, while chromosomes organize this genetic material inside the nucleus of the cell.
This chapter also explains important concepts like genes, RNA, transcription, mutations, and protein synthesis. These topics help students understand how traits are expressed and how proteins are formed in living organisms.
These notes are specially prepared for Class 12 Punjab Board students, keeping in mind exam requirements, short questions, and MCQs to make preparation easy and effective.
📥 Download Class 12 Biology Unit 20 – Chromosomes and DNA
Skip to PDF contentGet complete, easy-to-understand and exam-focused notes of Class 12 Biology Unit 20 in one PDF file. These notes are specially designed for Punjab Board students to help in quick revision and better exam preparation.
👉 Download PDF: Class 12 Biology Unit 20 – Chromosomes and DNA Complete Notes
❓ FAQs
Q1: What are chromosomes?
Chromosomes are thread-like structures made of DNA and proteins found in the nucleus. They carry genetic information from one generation to the next.
Q2: What is a gene?
A gene is a specific segment of DNA that contains instructions to produce a particular protein or determine a trait.
Q3: What is transcription?
Transcription is the process in which genetic information from DNA is copied into RNA. It is the first step of protein synthesis.
Q4: What are the main types of RNA?
There are three main types of RNA:
- mRNA (Messenger RNA): carries genetic information from DNA to ribosomes.
- tRNA (Transfer RNA): brings amino acids to the ribosome for protein synthesis.
- rRNA (Ribosomal RNA): forms part of the ribosome structure and helps in protein synthesis.
Q5: What was Frederick Sanger’s contribution to protein science?
In 1953, Frederick Sanger sequenced the complete amino acid sequence of insulin, proving that proteins have a specific and definite order of amino acids.
📝 MCQs – Chromosomes and DNA
1. What is the full form of DNA?
A) Deoxyribose Nucleic Acid
B) Deoxyribonucleic Acid ✔
C) Dioxyribo Acid
D) None
2. What is the main function of chromosomes?
A) Protein synthesis
B) Storing genetic information ✔
C) Energy production
D) RNA synthesis
3. Which enzyme is most important during DNA replication?
A) RNA polymerase
B) DNA polymerase ✔
C) Ligase
D) Helicase
4. What is the product of transcription?
A) Protein
B) DNA copy
C) RNA ✔
D) Amino acids
5. What are the types of RNA?
A) mRNA, tRNA, rRNA ✔
B) mRNA, dRNA, rRNA
C) tRNA, gRNA, rRNA
D) rRNA, sRNA, mRNA
6. What is the major difference between DNA and RNA?
A) DNA is single-stranded, RNA is double-stranded
B) DNA is double-stranded, RNA is single-stranded ✔
C) DNA has ribose sugar, RNA has deoxyribose sugar
D) DNA has uracil, RNA has thymine
7. What is the correct sequence of protein synthesis?
A) Transcription → Translation ✔
B) Translation → Transcription
C) DNA replication → Transcription
D) Replication → Translation