Genetics

Step 1: Nondisjunction का परिचय.
Nondisjunction में chromosomes meiosis के दौरान सही ढंग से अलग नहीं होते, जिससे chromosomal disorders होते हैं।

Step 2: Down syndrome.
Down syndrome autosomal nondisjunction के कारण होता है, विशेषकर 21वें chromosome की trisomy से।

Step 3: अन्य विकल्पों का विश्लेषण.
(B) क्लाइनफेल्टर सिंड्रोम और (C) टर्नर सिंड्रोम → sex chromosome nondisjunction से।

Step 4: निष्कर्ष.
सही उत्तर है (D) डाउन सिंड्रोम।

Step 1: परिचय.
एडीनोसिन डिअमिनेज (Adenosine deaminase, ADA) एक महत्वपूर्ण एंजाइम है जो purine metabolism में कार्य करता है। इसका मुख्य कार्य एडीनोसिन (Adenosine) को Inosine में बदलना है।

Step 2: जैविक महत्व.
- यह एंजाइम प्रतिरक्षा प्रणाली (immune system) के सही कार्य के लिए आवश्यक है।
- ADA की कमी होने पर गंभीर रोग SCID (Severe Combined ImmunoDeficiency) हो सकता है, जिसमें रोगी की प्रतिरक्षा क्षमता बहुत कम हो जाती है।

Step 3: निष्कर्ष.
एडीनोसिन डिअमिनेज एंजाइम का अध्ययन मानव आनुवंशिकी और प्रतिरक्षा विज्ञान में अत्यधिक महत्वपूर्ण है। ADA deficiency gene therapy का एक प्रमुख क्षेत्र है।

Step 1: Hemophilia का परिचय.
Hemophilia एक genetic disorder है, जो मनुष्यों (humans) में पाया जाता है। इसमें रक्त का थक्का नहीं जमता।

Step 2: अन्य विकल्पों का विश्लेषण.
(A) बिल्ली, (B) कुत्ता, (D) घोड़ा → इनमे यह disorder नहीं होता।

Step 3: निष्कर्ष.
सही उत्तर है (C) मानव में।

Step 1: परिभाषा.
जीन उत्परिवर्तन (Gene mutation) DNA के nucleotide अनुक्रम में स्थायी परिवर्तन है।

Step 2: प्रकार.
- Substitution mutation – एक base के स्थान पर दूसरा जुड़ना।
- Deletion/Insertion mutation – एक या अधिक bases का हटना/जुड़ना।
- Frameshift mutation – reading frame बदल जाना।

Step 3: प्रभाव.
- प्रोटीन संश्लेषण प्रभावित होता है।
- कई बार आनुवंशिक बीमारियाँ (जैसे Sickle cell anaemia, Thalassemia) होती हैं।

Step 4: निष्कर्ष.
जीन उत्परिवर्तन वंशानुगत परिवर्तन और विकास (Evolution) दोनों का मूल स्रोत है।

Step 1: Gamete chromosome number.
मानव के somatic cells में 46 (2n) chromosomes होते हैं। Gametes (sperm और ovum) haploid होते हैं, इसलिए इनमें 23 chromosomes पाए जाते हैं।

Step 2: विकल्पों का विश्लेषण.
(A) 21 → गलत, यह कम है।
(B) 44 → diploid number का हिस्सा है, लेकिन gametes में नहीं।
(D) 46 → यह diploid संख्या है।

Step 3: निष्कर्ष.
सही उत्तर है (C) 23।

Step 1: Autopolyploidy का परिचय.
स्वबृंहगुणिता (Autopolyploidy) वह स्थिति है जिसमें किसी पौधे में chromosome की संख्या दोगुनी या अधिक कर दी जाती है। इसे कृत्रिम रूप से induce किया जा सकता है।

Step 2: Colchicine का कार्य.
Colchicine mitotic spindle के निर्माण को रोकता है, जिससे chromosomes विभाजित तो होते हैं पर daughter cells में अलग नहीं हो पाते और chromosome संख्या दोगुनी हो जाती है।

Step 3: अन्य विकल्प.
(B) क्लोरोफॉर्म → anaesthetic है।
(C) कोल्चिसेमिन और (D) क्लोरोसिन → अप्रासंगिक।

Step 4: निष्कर्ष.
सही उत्तर है (A) कोल्चिसिन द्वारा।

The sex-determination system in honeybees is unique, as it follows a system known as the haplodiploid system, which is different from the XY or XX system seen in many other species. Step 1: Basic Mechanism.
- Haplodiploidy means that males are haploid (having only one set of chromosomes) and females are diploid (having two sets of chromosomes). - The queen bee lays both fertilized and unfertilized eggs: - Fertilized eggs develop into female bees (workers or queens). - Unfertilized eggs develop into male bees (drones).
Step 2: Chromosome Determination.
- In females (workers and queens), the egg is fertilized by sperm from the male drone. The fertilized egg receives one chromosome set from the mother and one from the father, making it diploid. - In males (drones), the egg is not fertilized, so the egg only contains the mother's genetic material, making the male haploid (one set of chromosomes).
Step 3: Queen and Drone Differentiation.
- The queen bee and worker bees are both female, but their roles are determined by diet during the larval stage. A female larva that is fed a special diet called royal jelly will develop into a queen, while the others develop into worker bees.
Final Answer: In honeybees, males are haploid (developing from unfertilized eggs), while females are diploid (developing from fertilized eggs). The queen's fate is determined by diet during the larval stage.

Epistasis refers to the interaction between different genes, where one gene can mask or modify the expression of another gene. Step 1: Understanding epistasis.
- In epistasis, one gene (the epistatic gene) suppresses or alters the expression of another gene (the hypostatic gene) at a different locus.
Step 2: Types of epistasis.
1. Recessive epistasis: The epistatic gene must be homozygous recessive to mask the expression of the other gene. 2. Dominant epistasis: A dominant allele at the epistatic gene locus can suppress the expression of the other gene, regardless of its genotype.
Final Answer: Epistasis is the genetic interaction where one gene suppresses or modifies the expression of another gene at a different locus.

Sickle cell anemia is a genetic disorder that affects red blood cells. Step 1: Symptoms of sickle cell anemia.
1. Pain episodes - Due to the sickle-shaped cells blocking blood flow, individuals often experience episodes of severe pain. 2. Fatigue - The sickle-shaped cells cannot carry enough oxygen, leading to tiredness and weakness.
Final Answer: 1. Pain episodes 2. Fatigue

Klinefelter syndrome is a genetic condition in which a male has an extra X chromosome, leading to various physical, cognitive, and reproductive issues. Step 1: Cause of Klinefelter syndrome.
Klinefelter syndrome occurs when a male inherits an additional X chromosome (XXY instead of the typical XY), which results in 47 chromosomes instead of the usual 46.
Step 2: Symptoms and characteristics.
- Reduced testosterone production. - Underdeveloped secondary sexual characteristics (e.g., reduced facial hair, smaller testes). - Learning difficulties and speech problems in some individuals.
Final Answer: Klinefelter syndrome is a genetic condition in males with an extra X chromosome, leading to physical and cognitive symptoms.

Step 1: Understand the factors affecting skin colour.
Skin colour in humans is influenced by multiple genetic factors and environmental influences. The genetic determination is primarily controlled by multiple genes, which exhibit both quantitative and qualitative traits.
Step 2: Analyze the options.
- Quantitative traits refer to those influenced by many genes with small effects. Skin colour is partly quantitative as it is influenced by several genes. - Multiple gene involvement means more than one gene contributes to the phenotype, which is true for skin colour. - Qualitative traits are those that exhibit distinct categories, but skin colour does not fit perfectly into distinct qualitative categories. However, it is also influenced by qualitative genetic variation.
Step 3: Conclusion.
Since skin colour involves both quantitative genetic contributions and multiple genes, the correct answer is ((D) All of these.
Final Answer:

Step 1: Understand Neurospora reproduction.
In Neurospora, the formation of ascospores follows a sequence of nuclear divisions. The ascospore formation involves both mitosis and meiosis.
Step 2: Analyze the process.
- First, meiosis occurs, which results in the formation of haploid cells. - Then, mitosis occurs to produce the 8 ascospores, ensuring that each spore has the correct genetic makeup.
Step 3: Conclusion.
Thus, the correct process for forming 8 ascospores is ((D), which involves 1 meiosis followed by 1 mitosis.
Final Answer:

Step 1: Understanding linkage groups.
Linkage groups refer to groups of genes that tend to be inherited together due to their physical proximity on a chromosome. In humans, the number of linkage groups corresponds to the number of chromosomes.
Step 2: Analyze the options.
- 46: Humans have 46 chromosomes, but this is not the number of linkage groups. - 22: There are 23 pairs of chromosomes, so this is incorrect. - 92: This is not the correct number of linkage groups for humans. - 23: Humans have 23 pairs of chromosomes, which are the linkage groups in human beings.
Step 3: Conclusion.
The correct answer is (D) 23, as humans have 23 pairs of chromosomes, which represent the linkage groups.
Final Answer:

Step 1: Understanding basic number of chromosomes.
The basic number of chromosomes refers to the number of chromosomes in a gamete (sperm or egg) and is denoted by "n." This number represents the haploid number, which is half of the diploid number (2n) found in somatic cells.
Step 2: Analyze the options.
- n: This represents the haploid number, which is the correct answer. - 2n: This represents the diploid number, which is twice the basic number of chromosomes. - 4n: This would indicate a tetraploid number of chromosomes, which is incorrect. - n/2: This does not represent a correct number of chromosomes.
Step 3: Conclusion.
The basic number of chromosomes is "n," which refers to the haploid number in a gamete.
Final Answer:

Step 1: Understand sex-linked traits.
Sex-linked traits are those that are associated with the sex chromosomes (X and Y). These traits are often found on the X chromosome and can result in certain conditions being more common in one sex.
Step 2: Review the options.
- Anaemia, specifically sickle cell anaemia, can be inherited as a sex-linked trait, though not as commonly. - Colourblindness and baldness are classic examples of sex-linked traits. They are often passed on through the X chromosome, with males being more likely to express these traits due to having only one X chromosome.
Step 3: Conclude.
All three conditions—anaemia, colourblindness, and baldness—can be sex-linked, making option (D) the correct answer.
Final Answer:

Step 1: Understand chromosomal abnormalities.
- Trisomy occurs when there is one extra chromosome, making the total number of chromosomes 47 instead of the normal 46 (e.g., Down syndrome with an extra chromosome 21). - Double trisomy involves two extra chromosomes. - Tetrasomy refers to the presence of an extra pair of chromosomes (four copies of a chromosome). - Nullisomy occurs when there is a loss of both chromosomes from a pair.
Step 2: Review the options.
- Trisomic refers to the condition where an organism has one extra chromosome. This is a known chromosomal abnormality. - Double trisomic refers to having two extra chromosomes, not just one. - Tetrasomic refers to having four copies of a chromosome. - Nullisomic refers to the absence of both chromosomes from a pair.
Step 3: Conclude.
The correct term for having an extra pair of chromosomes is trisomic, so option (A) is the correct answer.
Final Answer:

Step 1: Understand codominance.
In codominance, both alleles contribute equally and visibly to the organism's phenotype, unlike incomplete dominance where the phenotype is an intermediate blend.
Step 2: Review the options.
- The 3:1 ratio is observed in incomplete dominance, not codominance.
- The 1:3 ratio is incorrect for codominance, as it does not apply to F2 generation.
- The 1:2:1 ratio is characteristic of codominance, where both alleles are expressed equally in the phenotype.
- The 1:1 ratio is seen in monohybrid crosses with a dominant and recessive allele, but it doesn't apply to codominance.
Step 3: Conclude.
The correct phenotypic ratio for F2 generation in case of codominance is 1 : 2 : 1, making option (C) the correct answer.
Final Answer: