Genetics

Step 1: Understanding Klinefelter’s Syndrome

- Klinefelter’s syndrome is a genetic disorder in males caused by an extra X chromosome (XXY).
- Affected individuals have 47 chromosomes.
Step 2: Conclusion

Since Klinefelter’s syndrome is characterized by 47(XXY), the correct answer is Option (3).

Step 1: Understanding Blood Group Inheritance

- Blood group A (homozygous) = AA
- Blood group B (homozygous) = BB
- Their offspring inherit one allele from each parent → AB.
Step 2: Possible Blood Groups in Children

- Offspring will have the AB blood group.
- A, B, and O blood groups are not possible.
Step 3: Conclusion

Since A, B, and O blood groups are not expected, the correct answer is Option (2).

Step 1: Understanding the Sex Index Ratio

- Sex determination in *Drosophila* depends on the X/A ratio (number of X chromosomes to autosome sets).
- A sex index of 0.33 indicates Metamale.

Step 1: Understanding STDs and Their Causative Agents

- Gonorrhea is caused by *Neisseria gonorrhoeae*. - Syphilis is caused by *Treponema pallidum*. - Genital warts are caused by the Human papilloma virus (HPV).
Step 2: Correcting the Incorrect Pair

- Cervical cancer is primarily associated with HPV, not Herpes simplex virus. - Herpes simplex virus (HSV) is responsible for genital herpes.
Step 3: Conclusion

Since Cervical cancer is incorrectly linked to Herpes simplex virus, the correct answer is Option (3).

Step 1: Understanding Turner's Syndrome:
Turner's syndrome is a chromosomal disorder in females caused by the absence of one of the X chromosomes. This is a case of monosomy .
Step 2: Analyzing the Karyotype:

• Normal Human Karyotype: 46 chromosomes (44 autosomes + 2 sex chromosomes).
• Turner's Syndrome: Loss of one X chromosome.
• Total Chromosomes: .
• Sex Chromosomes: Only one X is present (denoted as XO).
• Notation: 45, X or sometimes written with autosomes as AA + XO.

Step 3: Analyzing Other Options:
(B) 47, XXY represents Klinefelter's Syndrome.
(C) 47, XX + 13 represents Patau Syndrome (Trisomy 13).
(D) 47, XX + 18 represents Edwards Syndrome (Trisomy 18).
Step 4: Final Answer:
The correct karyotype is 45, X [AA + XO].

Step 1: Determine Genotypes:
Colour blindness is an X-linked recessive disorder.

• Colour blind man:
• Carrier woman: (where is normal, is the colorblind allele)

Step 2: Perform the Cross:
Parents: (Female) (Male) \begin{center} \begin{tabular}{|c|c|c|} \hline Gametes & (Male) & (Male)
\hline (Female) & (Carrier Daughter) & (Normal Son)
\hline (Female) & (Colour blind Daughter) & (Colour blind Son)
\hline \end{tabular} \end{center}
Step 3: Calculate Probability:
Total possible children genotypes: 4 ( ).

• Colour blind children: (Daughter) and (Son).
• Number of colour blind children = 2.
• Total children = 4.
• Percentage = .

Step 4: Final Answer:
The chance of children being colour blind is 50%.

Step 1: Analyze Assertion (A):
Skin colour in humans is controlled by three (or more) pairs of genes (usually denoted as A, B, C). Traits controlled by multiple genes are called Polygenic traits (or Quantitative inheritance). Thus, (A) is true.
Step 2: Analyze Reason (R):
In polygenic inheritance, each dominant allele contributes a small amount to the phenotype (e.g., melanin production). The final phenotype is the result of the additive or cumulative effect of all the dominant alleles present in the genotype. For example, AABBCC is darkest, aabbcc is lightest, and AaBbCc is intermediate. This mechanism (cumulative effect) is the definition and explanation of how a polygenic trait works. Thus, (R) is true and explains (A).

Step 1: Analyze Each Pair:

• (A) Lactational amenorrhea: Absence of menstruation during intense breastfeeding. It is a Natural method of contraception. (Correct pair).
• (B) Vaults: Rubber caps inserted into the female reproductive tract to cover the cervix. They are Barrier methods. (Correct pair).
• (C) Multiload 375: A copper-releasing IUD. It is an Intrauterine Device. (Correct pair).
• (D) Saheli: Saheli is a non-steroidal preparation (Centchroman) taken as a pill (once a week). It is an Oral Contraceptive Pill, NOT an implant. Implants are subcutaneous devices containing progesterone/estrogen (e.g., Norplant). (Incorrect/Odd pair).

Step 2: Conclusion:
Option (D) is the odd pair because the classification is wrong.

• I is correct: I{A} and I{B} are both dominant over I{O}; I{A} and I{B} are co-dominant with each other.
• II is correct: in birds (and some reptiles/fish) females are ZW (heterogametic) and males ZZ (homogametic).
• III is incorrect: genic balance theory relates X:autosome ratio, not presence of Y — Y is not essential for male Drosophila (it carries male fertility genes but sex is determined by X:A ratio).
• IV is false: O group individuals lack A and B antigens (that's why they are universal donors), but the statement incorrectly says their RBC contain both antigens — wrong.
• Therefore correct statements are I, II → option (1).

• Gonorrhea is caused by Neisseria gonorrhoeae — correct.
• Genital herpes is caused by Herpes simplex virus (HSV), not Human papilloma virus (HPV) — this is the mismatched pair.
• AIDS is caused by HIV — correct.
• Syphilis is caused by Treponema pallidum — correct.
• Hence the mismatched pair is (2).

• Homozygous A = genotype I\textsuperscript{A}I\textsuperscript{A}, Homozygous B = I\textsuperscript{B}I\textsuperscript{B}.
• All offspring will receive I\textsuperscript{A} from one parent and I\textsuperscript{B} from the other → genotype I\textsuperscript{A}I\textsuperscript{B} → phenotype AB only.
• Therefore blood groups A, B and O are **not expected** among the children (only AB is expected).
• Hence the correct answer is (3) A, B and O.

Holandric genes are located on the non-homologous region of Y chromosome, transmitted strictly from father to son. Y-chromosome is male-specific, explaining the male-limited inheritance pattern.

• Male hymenopterans (e.g., honeybee drones) are haploid — they develop from unfertilised eggs (arrhenotoky).
• In haploid males, spermatogenesis proceeds by mitotic divisions (there is no meiosis because cells are already haploid) — so A is true and R explains it.
• Therefore the correct choice is (1).

For a gene with four alleles (A1, A2, A3, A4), the number of genotypes is calculated using formula: for homozygous and heterozygous combinations. Here , so number of genotypes = for heterozygotes plus 4 homozygotes = 14? Wait, let's carefully calculate: - Homozygotes: A1A1, A2A2, A3A3, A4A4 → 4 - Heterozygotes: A1A2, A1A3, A1A4, A2A3, A2A4, A3A4 → 6 Total = 4 + 6 = 10.

I. True — Haemophilia-A/B are X-linked recessive disorders. II. False — In sickle cell anaemia, glutamic acid is replaced by valine, not vice versa. III. True — Protonopia is red colour blindness (red cones defect). IV. False — Phenylketonuria is autosomal recessive, not allosomal.

Gonorrhea: Neisseria gonorrhoeae; Syphilis: Treponema pallidum; Chlamydiasis: Chlamydia trachomatis; Genital warts: Human papilloma virus (HPV). Correctly match diseases with their causal agent.