Principles of Inheritance and Variation — NEET UG practice

1. Recall the sex-determination system in grasshoppers. Grasshoppers follow the XX-XO type of sex determination, where females carry a pair of X chromosomes and males carry only a single X chromosome with no corresponding partner.

2. Write the sex chromosome makeup of each sex. Given that the autosome number stays the same in both sexes,

$$\text{Female} = \text{Autosomes} + XX, \qquad \text{Male} = \text{Autosomes} + X0$$

3. Compare total chromosome counts. Since the male has one fewer chromosome than the female (missing the second X),

$$\text{Male total} = \text{Female total} - 1$$

4. Apply this to the given numbers. Therefore, the member with 23 chromosomes must be the male, and the member with 24 chromosomes must be the female.

Hence, the correct answer is Option C, males and females, respectively.

1. Recall how sex is determined in honeybees. In honeybees, sex is decided by the number of chromosome sets an individual receives, not by a pair of sex chromosomes like in humans.

2. Check the fate of a fertilised egg. When a sperm fuses with an egg, the resulting individual is diploid, and it develops into a female — either a queen or a worker.

So, Statement A is true.

3. Check the fate of an unfertilised egg. An egg that develops without fertilisation (a process called parthenogenesis) grows into a male (drone), which is haploid.

So, Statement B is true.

4. Compare the chromosome numbers of males and females. Since females (diploid) have 32 chromosomes and males (haploid) have 16 chromosomes,

$$\text{Male chromosome number} = \frac{1}{2} \times \text{Female chromosome number}$$

So, Statement C is true.

5. Check how males produce sperm. Because males are already haploid, they cannot undergo a normal reduction division (meiosis) to halve their chromosome number further. Instead, they produce sperm by mitosis, not meiosis.

So, Statement D is false.

6. Name this overall system. Since males are haploid and females are diploid, this system of sex determination is called the haplodiploid system.

So, Statement E is true.

7. Combine the correct statements. Since A, B, C, and E are true while D is false,

Hence, the correct answer is Option A, A, B, C and E only.

1. Recall the molecular basis of sickle-cell anaemia. This disorder arises due to a change (mutation) in a single gene, the gene that codes for the beta chain of haemoglobin.

2. Identify the exact molecular change. Given that the mutation causes glutamic acid to be replaced by valine specifically at the sixth position of the beta chain,

$$\text{Glutamic acid (position 6)} \rightarrow \text{Valine (position 6)}$$

this abnormal haemoglobin molecule causes red blood cells to become sickle (crescent) shaped, especially under low oxygen conditions.

3. Eliminate the other disorders. Thalassemia results from a reduced rate of synthesis of globin chains, not an amino acid substitution. Phenylketonuria results from a defect in an enzyme that metabolises phenylalanine. Haemophilia results from a defect in a blood clotting factor, unrelated to haemoglobin structure.

Hence, the correct answer is Option B, Sickle-cell anaemia.