Which one of the following disorders is caused by the substitution of Glutamic acid (Glu) by Valine (Val) at the sixth position of the beta globin chain of the haemoglobin molecule?

Related Formula

Incomplete dominance: Antirrhinum flower colour Codominance: ABO Blood Group (I^A I^B$I^A I^B$) Pleiotropy: Single gene arrow$\rightarrow$ Multiple phenotypic effects (PKU) Polygenic: Multiple genes arrow$\rightarrow$ Single trait (Skin colour)

Core Logic

• Incomplete dominance: Flower colour in Antirrhinum sp. (Snapdragon) arrow$\rightarrow$ II
• Co-dominance: ABO blood group system arrow$\rightarrow$ IV
• Pleiotropy: Phenylketonuria in humans arrow$\rightarrow$ III
• Polygenic inheritance: Human skin colour arrow$\rightarrow$ I

Step 1: Match Verification

The correct combination is A-II, B-IV, C-III, D-I. Correct option is (1).

Pattern Recognition

Incomplete dominance = Antirrhinum (A-II). Polygenic = Human skin colour (D-I). Matches option (1).

Chapter Mix

Class 12 Biology: Principles of Inheritance and Variation

Related Formula

Honeybee Sex Determination: Haplodiploid system. Female (2n = 32$2n = 32$) Meiosis$\xrightarrow{\text{Meiosis}}$ Eggs (n = 16$n = 16$) Male (n = 16$n = 16$) Mitosis$\xrightarrow{\text{Mitosis}}$ Sperms (n = 16$n = 16$)

Core Logic

• A: Fertilized egg (2n$2n$) arrow$\rightarrow$ Female (True).
• B: Unfertilized egg (n$n$) arrow$\rightarrow$ Male by parthenogenesis (True).
• C: Male (n=16$n=16$) has half the chromosome count of female (2n=32$2n=32$) (True).
• D: Males are haploid, so they produce sperms by MITOSIS, not meiosis (False).
• E: It is a haplodiploid system (True).

Step 1: Conclusion

Correct statements are A, B, C, and E. Option (4) is correct.

Pattern Recognition

Haploid male honeybees produce sperm by MITOSIS (D is False). Eliminating D immediately isolates A, B, C, E.

Chapter Mix

Class 12 Biology: Principles of Inheritance and Variation

Related Formula

Normal codon (GAG) Point mutation (A arrow U) Mutant codon (GUG) arrow Valine (Val)$\text{Normal codon (GAG)} \xrightarrow{\text{Point mutation (A } \rightarrow \text{ U)}} \text{Mutant codon (GUG)} \rightarrow \text{Valine (Val)}$

Core Logic

Sickle-cell anaemia is caused by a point mutation in the beta-globin gene. The normal 6th codon GAG is mutated to GUG in mRNA. This leads to the substitution of Glutamic acid (Glu) by Valine (Val) at the 6th position of the beta-globin polypeptide chain, causing polymerisation under low oxygen tension and distorting RBCs into a sickle shape.

Step 1: Identification of Mutant Codon

The normal codon is GAG and the mutant codon is GUG.

Pattern Recognition

Sees: "sixth mutant codon beta globin gene". Shortcut: Normal = GAG (Glutamic acid), Mutant = GUG (Valine).

Chapter Mix

Class 12 Biology: Principles of Inheritance and Variation

Related Formula

Core Logic

Mother's genotype (heterozygous A) = I^A i$I^A i$ Father's genotype (heterozygous B) = I^B i$I^B i$

Crossing these parents yields four possible genotypes in equal proportions (1 : 1 : 1 : 1):

• I^A I^B$I^A I^B$ (Blood group AB)
• I^A i$I^A i$ (Blood group A)
• I^B i$I^B i$ (Blood group B)
• i i$i i$ (Blood group O)

Step 1: Calculation of Probability

Pattern Recognition

Sees: "heterozygous A and B parents blood group O probability". Shortcut: Cross I^A i × I^B i$I^A i \times I^B i$ gives 1/4 = 25% for each blood group (A, B, AB, O).

Chapter Mix

Class 12 Biology: Principles of Inheritance and Variation