CBSE Class 12 Biology Principles of Inheritance and Variation Diagrams

CBSE Class 12 Biology Principles of Inheritance and Variation Diagrams. Please refer to the examination notes which you can use for preparing and revising for exams. These notes will help you to revise the concepts quickly and get good marks.

PRINCIPLES  OF INHERITANCES 

MENDEL`S DIHYBIRD CROSS

Class 12 Biology diagrams for Chapter 5 Principles of Inheritance and Chapter 6 Molecular Basis of Inheritance, covering Mendel's dihybrid cross, the structure of a polynucleotide chain, nucleosome, replication fork of DNA, Hershey and Chase experiment, tRNA adapter molecule, Meselson and Stahl's experiment, structure of a transcription unit and the lac operon, as per the CBSE syllabus.

CHAPTER 5 PRINCIPLES OF INHERITANCE

1. MENDEL'S DIHYBRID CROSS

[Figure: Mendel's dihybrid cross. P generation: Round yellow (RRYY) crossed with Wrinkled green (rryy). Gametes of P generation: RY and ry. F1 generation: Round yellow (RrYy), obtained by selfing. Gametes of F1 generation shown as RY, Ry, rY and ry on the female and male sides. F2 generation shown as a diamond-shaped 4 x 4 Punnett square with genotypes RRYY, RRYy, RrYY, RrYy, RRyy, Rryy, rrYY, rrYy and rryy. Phenotypic ratio: round yellow : round green : wrinkled yellow : wrinkled green = 9 : 3 : 3 : 1]

CHAPTER 6 MOLECULAR BASIS OF INHERITANCE

1. Double stranded polynucleotide chain

[Figure: Double stranded polynucleotide chain labelled POLYNUCLEOTIDE STRANDS. Each strand has a sugar with phosphate (P) linkages. The 5' end is at the top left of one strand and the 3' end (OH) is at the top right. The opposite strand runs from 3' (HO) at the bottom left to 5' at the bottom right. Bases are paired with hydrogen bonds shown by dotted lines: A (top left strand) with T (opposite strand), T with A, G with C, and C with G. Hydrogen bonds are marked by a red arrow.]

2. NUCLEOSOME

[Figure: Nucleosome. A DNA strand (labelled DNA) is wrapped around a core of histone molecules. The core is labelled Histone octamer. The H1 histone is shown on the outside of the DNA. The whole core is labelled Core of histone molecules.]

3. REPLICATION FORK OF DNA

[Figure: Replication fork of DNA. Two template DNA strands (parental strands) are shown as blue lines with 5' and 3' ends marked. The newly synthesised strands are shown in red. One new strand is synthesised continuously, running 5' to 3' towards the fork, labelled Continuous synthesis. The other new strand is synthesised discontinuously in short pieces, labelled Discontinuous synthesis, with arrows running 5' to 3' away from the fork. The new strands are labelled Newly synthesised strands.]

4. HERSHEY AND CHASE EXPERIMENT

[Figure: Hershey and Chase experiment with a bacteriophage. Left side: bacteriophage with radioactive (35S) labelled protein capsule. Right side: bacteriophage with radioactive (32P) labelled DNA. Three steps are shown in order: 1. Infection, 2. Blending, 3. Centrifugation. Left side result: no radioactive (35S) detected in cells, and radioactive (35S) detected in supernatant. Right side result: radioactive (32P) detected in cells, and no radioactivity detected in supernatant.]

5. tRNA- adapter MOLECULE

[Figure: tRNA adapter molecule drawn in cloverleaf form. The amino acid Tyr is attached at the top end of the molecule. The anticodon loop at the bottom carries the bases A, U, G, shown above the mRNA. The mRNA strand is shown below with the codon bases U, A, C.]

6. MESELSON AND STAHL'S EXPERIMENT

[Figure: Meselson and Stahl's experiment. Starting DNA is labelled 15N-DNA (heavy). After 20 minutes, Generation I shows 15N-14N hybrid DNA. After 40 minutes, Generation II shows a mix of 14N-DNA (light) and 15N-14N hybrid DNA. Separation of DNA by centrifugation under gravitational force is shown in test tubes: Heavy (15N-15N), Hybrid (15N-14N) and Light (14N-14N) bands.]

7. STRUCTURE OF TRANSCRIPTION UNIT

[Figure: Structure of a transcription unit. The transcription start site is marked by an arrow. The promoter is shown at the left, on the 3' to 5' template strand. The structural gene lies between the promoter and the terminator. The terminator is shown at the right on the template strand. The template strand runs 3' to 5' (top) and the coding strand runs 5' to 3' (bottom).]

8. LAC OPERON

[Figure: Lac operon. The operon has the regions P (promoter), i (regulator gene), P, o (operator), z, y and a. In presence of inducer: the repressor mRNA is translated into repressor, the repressor binds to the operator region (o) and prevents RNA polymerase from transcribing the operon. In absence of inducer: the operon is transcribed into lac mRNA, which is translated into beta-galactosidase, permease and transacetylase. The inducer binds to the repressor to form an inactive repressor.]