all r

In which part of the nephron does maximum reabsorption of glomerular filtrate occur?
A) Loop of Henle
B) Collecting duct
C) Distal convoluted tubule
D) Proximal convoluted tubule

The correct answer is D) Proximal convoluted tubule.

🔵 Explanation:

• Maximum reabsorption (about 70-80%) of water, glucose, amino acids, and salts happens in the proximal convoluted tubule (PCT).

• The collecting duct mainly adjusts water and electrolyte balance, but most reabsorption happens earlier, at the PCT.

Which of the following processes does not occur in the renal tubules?
A) Filtration
B) Reabsorption
C) Secretion
D) Concentration of urine

🔵 Explanation:

• Filtration happens only at the glomerulus (inside Bowman's capsule), before the renal tubules start.

• Reabsorption, secretion, and concentration all happen inside the renal tubules (PCT, loop of Henle, DCT, and collecting duct).

Process	Where it happens	Quick explanation
Filtration	ONLY at Glomerulus (Bowman's capsule)	Blood pressure forces small molecules (water, salts, glucose, urea) from blood into Bowman's capsule. This happens before the renal tubules start.
Reabsorption	In tubules (mainly PCT)	Good things like glucose, amino acids, and salts are taken back into blood from the filtrate.
Secretion	In tubules (mainly DCT)	Extra waste (like drugs, ions) is added into the filtrate from blood.
Concentration	In Loop of Henle + Collecting Duct	Water is reabsorbed to concentrate the urine.

Process	Where it happens	Quick explanation
Filtration	ONLY at Glomerulus (Bowman's capsule)	Blood pressure forces small molecules (water, salts, glucose, urea) from blood into Bowman's capsule. This happens before the renal tubules start.
Reabsorption	In tubules (mainly PCT)	Good things like glucose, amino acids, and salts are taken back into blood from the filtrate.
Secretion	In tubules (mainly DCT)	Extra waste (like drugs, ions) is added into the filtrate from blood.
Concentration	In Loop of Henle + Collecting Duct	Water is reabsorbed to concentrate the urine.

Which part of the nephron is mainly responsible for concentrating the urine? A) Proximal convoluted tubule B) Distal convoluted tubule C) Loop of Henle D) Bowman's capsule

Explanation:

• The Loop of Henle plays the main role in concentrating urine.

• Especially the descending limb (permeable to water) and the ascending limb (permeable to ions like Na⁺ and Cl⁻ but not to water).

• This sets up a counter-current mechanism, creating a high osmolarity in the medullary interstitium.

• This draws water out from the filtrate later (especially at the collecting duct under the influence of ADH), concentrating the urine.

• ADH → Aqua-porins → Water

• Aldosterone → Sodium

ADH (antidiuretic hormone) primarily increases the reabsorption of which substance in the kidney?
A) Urea
B) Glucose
C) Water
D) Sodium

1. Site of Action

   • ADH acts on the collecting ducts and late distal tubules of the nephron.

2. Mechanism

   • It binds to receptors on the cells lining these tubules.

   • This triggers insertion of aquaporin-2 water channels into their membranes.

   • Result: the tubes become highly permeable to water, so water moves out of the tubule back into the blood.

3. Effect on Urine

   • More water is reabsorbed → less water is lost as urine → urine becomes more concentrated.

In a healthy adult, the typical daily volume of urine excreted is approximately:
A) 1.5 mL
B) 15 mL
C) 1.5 L
D) 5 L

Blood enters kidney via Renal Artery

↓

Enters Glomerulus in Nephron

↓

✅ Step 1: Glomerular Filtration

• Blood plasma → Filtered in Bowman's Capsule

• Forms Filtrate (water, urea, glucose, salts)

↓

✅ Step 2: Tubular Reabsorption

• PCT: Glucose, amino acids, Na⁺, water reabsorbed

• Loop of Henle: Water (descending), Na⁺ (ascending)

• DCT: Selective reabsorption of ions, water

↓

✅ Step 3: Tubular Secretion

• DCT + Collecting Duct:

• Secretion of H⁺, K⁺, NH₃, drugs into filtrate

↓

✅ Concentration of Urine

• Loop of Henle + Vasa Recta = Countercurrent

• ADH ↑ water reabsorption in collecting duct

↓

💧 Final Urine → Collecting Duct

↓

Renal Pelvis → Ureter → Bladder

↓

Excreted through Urethra (Micturition)

Which part of the nephron is the primary site for tubular secretion of H⁺ and K⁺ ions?
A) Proximal convoluted tubule
B) Loop of Henle
C) Distal convoluted tubule
D) Bowman’s capsule

Explanation:

• Tubular secretion involves the transfer of substances from the blood into the tubular fluid. The distal convoluted tubule plays a significant role in the secretion of ions, including H⁺ (protons) and K⁺ (potassium ions). This is important for regulating the body's acid-base balance and potassium levels.

• The Loop of Henle (B) is primarily responsible for the reabsorption of water and salts, contributing to the concentration of urine, but it does not play a major role in secretion.

The accumulation of urea in the blood, often indicating renal failure, is termed:
A) Glycosuria
B) Uremia
C) Albuminuria
D) Oliguria

• Uremia refers to the accumulation of urea and other nitrogenous waste products in the blood, which often occurs due to kidney failure, as the kidneys are no longer able to filter out these wastes properly.

Which of the following substances is primarily reabsorbed in the proximal convoluted tubule of the nephron?

A) Water
B) Sodium ions
C) Glucose
D) Urea

This is because glucose is almost completely reabsorbed back into the bloodstream to prevent it from being lost in the urine. The transport mechanisms in the proximal convoluted tubule are highly efficient for glucose reabsorption.

Which structure prevents the backflow of urine from the urinary bladder into the ureters?
A) Sphincter muscles
B) Ureteral valves
C) Renal pelvis
D) Collecting ducts

"Urine formed by the nephrons is ultimately carried to the urinary bladder by the ureters. The bladder stores urine until a voluntary signal is given by the CNS. The stretch receptors in the bladder send signals for micturition. The oblique passage of the ureters through the bladder wall prevents the backflow of urine."

This "oblique passage" is what works like a valve to stop urine from flowing back.

Which part of the nephron reabsorbs the maximum amount of glomerular filtrate?

A) Loop of Henle
B) Distal convoluted tubule
C) Proximal convoluted tubule
D) Collecting duct

The Proximal Convoluted Tubule (PCT) is the main site for reabsorption in the nephron.

• It reabsorbs about 70-80% of the glomerular filtrate.

• It includes glucose, amino acids, Na⁺, Cl⁻, water, etc.

• Reabsorption here is mostly selective and active.

vWhich of the following is NOT used as a biofertilizer?
A) Rhizobium
B) Azotobacter
C) Clostridium
D) Pseudomonas

Pseudomonas

• Rhizobium: This bacterium is used as a biofertilizer, especially for leguminous plants, as it helps in nitrogen fixation by forming nodules on plant roots.

• Azotobacter: This is also a nitrogen-fixing bacterium used as a biofertilizer.

• Clostridium: This bacterium also aids in nitrogen fixation and is used as a biofertilizer in certain conditions.

• Pseudomonas: This bacterium is not typically used as a biofertilizer. It is more commonly associated with plant protection as it can act as a biocontrol agent, protecting plants from pathogens.

Azospirillum is commonly used as a biofertilizer for:
A) Leguminous crops only
B) Non-leguminous cereals (like wheat, rice)
C) All flowering plants
D) Fungi cultivation

B) Non-leguminous cereals (like wheat, rice).

Why B?

• Azospirillum is a free-living, associative nitrogen-fixing bacterium that colonizes the roots of non-leguminous crops such as cereals (e.g. rice, wheat, maize).

• It enhances their nitrogen uptake and growth, but it does not form root nodules like Rhizobium does on legumes.

Blue-green algae (cyanobacteria) used as biofertilizers in paddy fields belong to the genus:
A) Nostoc
B) Anabaena
C) Azotobacter
D) Rhizopus

The main benefit of using biofertilizers is that they:
A) Provide instant nitrogen to plants
B) Release nitrogen slowly and improve soil fertility
C) Eliminate the need for any fertilizers
D) Increase soil salinity

Explanation:

• Biofertilizers are organisms (like bacteria, fungi, and algae) that enhance the nutrient availability in the soil. They help to fix atmospheric nitrogen, decompose organic matter, and improve soil structure.

• The main advantage of biofertilizers is that they release nitrogen slowly, which enhances the soil's fertility over time and helps plants grow more sustainably. This is much better than chemical fertilizers, which can provide a quick release of nutrients but might harm the soil in the long term.

• Biofertilizers also help in maintaining the balance of soil nutrients, unlike chemical fertilizers which can lead to soil degradation.

Which part of the blastocyst is responsible for implantation into the uterine wall?
A) Inner cell mass
B) Zona pellucida
C) Trophoblast
D) Morula

Trophoblast is the correct answer.

Explanation:
The trophoblast is the outer layer of cells in the blastocyst. It helps the blastocyst attach to and invade the uterine wall, beginning the process of implantation. Later, the trophoblast gives rise to a part of the placenta.

What does the inner cell mass of the blastocyst develop into?
A) Placenta
B) Amniotic sac
C) Embryo
D) Trophoblast

• Inner cell mass (ICM) of the blastocyst develops into the embryo.

• The trophoblast is the outer layer that helps form the placenta.

• The amniotic sac forms later from extraembryonic structures, not directly from the ICM.

Which hormone released after fertilisation maintains the corpus luteum and supports early pregnancy?

A) LH (Luteinizing hormone)
B) FSH (Follicle stimulating hormone)
C) hCG (Human chorionic gonadotropin)
D) Progesterone

C) Embryo

Explanation:

• Inner cell mass (ICM) of the blastocyst develops into the embryo.

• The trophoblast is the outer layer that helps form the placenta.

• The amniotic sac forms later from extraembryonic structures, not directly from the ICM.

Which of the following events occurs immediately after the sperm penetrates the ovum?
A) Cleavage
B) Implantation
C) Cortical reaction
D) Blastocyst formation

Explanation:

• Once a sperm penetrates the ovum, the cortical reaction happens immediately. This is a defense mechanism to prevent entry of additional sperms (a process called polyspermy).

• Only after this reaction, zygote formation occurs, followed by cleavage (cell divisions), blastocyst formation, and finally implantation.

Which of the following organisms is NOT a source of restriction endonuclease?
A) Escherichia coli
B) Haemophilus influenzae
C) Streptococcus pneumoniae
D) Saccharomyces cerevisiae

✅ Correct Answer: D) Saccharomyces cerevisiae

“The first restriction endonuclease – Hind II, was isolated and characterized from Haemophilus influenzae.”

It also mentions other restriction enzymes and their bacterial origins, such as:

• EcoRI from Escherichia coli

• BamHI from Bacillus amyloliquefaciens

Which bacterium is the source of the thermostable DNA polymerase (Taq polymerase) used in PCR?
A) Escherichia coli
B) Thermus aquaticus
C) Bacillus subtilis
D) Pseudomonas putida

vCorrect answer: B) Thermus aquaticus

Explanation:
Taq polymerase, the enzyme used in PCR (Polymerase Chain Reaction), is derived from the bacterium Thermus aquaticus, which lives in hot springs. This enzyme can tolerate the high temperatures required for DNA denaturation in PCR, making it ideal for the process.

Which of the following is commonly used as a vector in recombinant DNA technology?
A) Rhizobium
B) Salmonella typhi
C) Agrobacterium tumefaciens
D) Escherichia coli

Explanation:

• Agrobacterium tumefaciens is a soil bacterium used as a natural genetic engineer because it can transfer part of its DNA (T-DNA from Ti plasmid) into plant genomes.

• It's commonly used as a vector to transfer genes into plants in genetic engineering.

Which of the following is true about plasmids used in genetic engineering?

A) Plasmids are found only in plants.
B) Plasmids are small, circular DNA molecules that replicate independently of chromosomal DNA.
C) Plasmids can only carry a few genes.
D) Plasmids are always harmful to the cell.

✅ Correct! Plasmids are small, circular DNA molecules that replicate independently of chromosomal DNA. They are commonly used in genetic engineering to carry foreign genes.

Which enzyme synthesizes the RNA primer required for DNA replication?
A) DNA polymerase I
B) DNA polymerase III
C) Primase
D) DNA ligase

Correct! Primase synthesizes the short RNA primer needed for DNA polymerases to start replication.

Which enzyme removes RNA primers and replaces them with DNA during replication?
A) DNA polymerase I
B) DNA polymerase III
C) RNase H
D) DNA ligase

• DNA polymerase I is responsible for removing RNA primers and replacing them with DNA during replication.

• RNase H is involved in removing the RNA strand from an RNA-DNA hybrid molecule, but not directly involved in replacing primers.

Which DNA polymerase is the main enzyme responsible for the bulk of DNA synthesis (elongation) in prokaryotes and also possesses 3′→5′ exonuclease (proofreading) activity?
A) DNA polymerase I
B) DNA polymerase II
C) DNA polymerase III
D) Primase

During replication, the lagging strand is synthesized in short fragments called:
A) Okazaki fragments
B) Replication forks
C) Primer fragments
D) Telomeres

✅ Correct! The lagging strand is synthesized in short fragments called Okazaki fragments.

Explanation:

• The Okazaki fragments are short segments of DNA that are synthesized on the lagging strand during DNA replication.

• These fragments are later joined together by DNA ligase to form a continuous strand.

Which of the following is a biosphere reserve in India (an in situ conservation unit)?
A) Gir National Park
B) Nanda Devi
C) Bhitarkanika
D) Keoladeo National Park

✅ Correct answer: B) Nanda Devi
Explanation:
In-situ conservation means protecting animals and plants in their natural habitat.

• Biosphere Reserves like Nanda Devi are examples of in situ conservation.

• Keoladeo National Park is also protected, but it's a national park, not specifically a biosphere reserve.

Question:
Which of the following is an example of ex situ conservation?
A) Sacred groves
B) National parks
C) Botanical gardens
D) Wildlife sanctuaries

C) Botanical gardens

Explanation:

• Ex situ conservation refers to protecting an endangered species by removing part of the population from a threatened habitat and placing it in a new location, which is often human-managed.
  🔹 Examples: Botanical gardens, zoological parks, seed banks, cryopreservation.

• In situ conservation involves protecting species in their natural habitat.
  🔹 Examples: National parks, wildlife sanctuaries, biosphere reserves, and sacred groves.

Each autonomic motor pathway consists of:

A) One motor neuron from CNS to effector
B) Two motor neurons in series from CNS to effector
C) Three motor neurons in series from CNS to effector
D) Only sensory neurons

Answer: B) Two motor neurons in series from CNS to effector

Explanation: ANS pathways always have a preganglionic neuron (in the CNS) synapsing at an autonomic ganglion, then a postganglionic neuron running to the effector. (NCERT Ch.21 “Autonomic Nervous System”)

2. The neurotransmitter released by parasympathetic postganglionic fibers is:

A) Norepinephrine
B) Acetylcholine
C) Dopamine
D) Epinephrine

Answer: B) Acetylcholine

Explanation: Both pre- and post-ganglionic parasympathetic neurons release ACh at their synapses. (NCERT Ch.21)

. The sympathetic outflow from the spinal cord arises from:

A) Cervical region only
B) Thoraco-lumbar region
C) Cranial nerves exclusively
D) Sacral region only

Answer: B) Thoraco-lumbar region

Explanation: Sympathetic preganglionic neurons originate in the thoracic and lumbar spinal segments. (NCERT Ch.21)

4. “Rest and digest” functions are mediated by which division?

A) Sympathetic
B) Parasympathetic
C) Somatic
D) Enteric

Answer: B) Parasympathetic

Explanation: Parasympathetic activity lowers heart rate, stimulates digestion, and conserves energy. (NCERT Ch.21)

5. Which brain region is the principal integrative center for autonomic functions?

A) Cerebellum
B) Hypothalamus
C) Midbrain
D) Medulla oblongata

Answer: B) Hypothalamus

Explanation: The hypothalamus regulates temperature, hunger, thirst, and coordinates sympathetic & parasympathetic outputs. (NCERT Ch.21 “Neural Control and Coordination”)

1. In cockroach, the forewings arise from the:
A) Prothorax
B) Mesothorax
C) Metathorax
D) Abdomen

Answer: B) Mesothorax

2. Total number of spiracles present in a cockroach is:
A) 8 pairs
B) 10 pairs
C) 2 pairs
D) 18 pairs

Answer: B) 10 pairs

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3. In cockroach, which structure stores sperms in females?
A) Mushroom gland
B) Vas deferens
C) Spermatheca
D) Colleterial gland

Answer: C) Spermatheca

4. The type of blood vascular system in cockroach is:
A) Closed
B) Open
C) Lymphatic
D) Mixed

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Answer: B) Open

5. The number of chambers in cockroach heart is:
A) 7
B) 10
C) 13
D) 5

Answer: C) 13

6. Mouthparts of cockroach are adapted for:
A) Sucking
B) Chewing and biting
C) Piercing and sucking
D) Sponging

Answer: B) Chewing and biting

7. The compound eyes of cockroach are made up of about:
A) 100 ommatidia
B) 1000 ommatidia
C) 2000 ommatidia
D) 10,000 ommatidia

Answer: C) 2000 ommatidia

8. Mushroom glands are found in the:
A) Male cockroach
B) Female cockroach
C) Both
D) Only in nymph

Answer: A) Male cockroach

9. The excretory organs of cockroach are:
A) Nephridia
B) Flame cells
C) Malpighian tubules
D) Green glands

Answer: C) Malpighian tubules

10. The development in cockroach is:
A) Complete metamorphosis
B) No metamorphosis
C) Incomplete metamorphosis
D) Direct

Answer: C) Incomplete metamorphosis (paurometabolous)

11. Anal styles are found in:
A) Female only
B) Male only
C) Both
D) Absent in cockroach

Answer: B) Male only

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12. What is the function of antennae?
A) Respiration
B) Excretion
C) Sensory (smell and touch)
D) Reproduction

Answer: C) Sensory (smell and touch)

13. In female cockroach, ootheca is formed by secretions of:
A) Spermatheca
B) Colleterial glands
C) Mushroom glands
D) Phallic gland

Answer: B) Colleterial glands

Genetics –

The branch of biology studying heredity and variation.

Inheritance –

The transmission of traits from parents to offspring. This is what keeps a mango seed from growing into an apple tree.

Variation –

The differences between offspring and their parents, or among siblings.

• Gregor Johann Mendel – Father of Genetics

• Performed hybridization experiments on garden pea plants (Pisum sativum)

• Duration: 1856 to 1863 (7 years)

• Applied statistical analysis & mathematical logic to biology for the first time!

• Observed inheritance patterns using large sampling size

👨‍🔬 Who was Mendel?

• Short life cycle

• Easy to grow

• Self-pollinating but can also be cross-pollinated

• Showed clear contrasting traits

Why Pea Plants (Pisum sativum)?

• Plants that show stable trait inheritance on continuous self-pollination

• Mendel used 14 true-breeding pea plant varieties

🌿 True-Breeding Lines

🔁

• Selected pairs of traits with one contrasting character each

• Performed artificial pollination / cross-pollination

• Observed results over successive generations

Experimental Design

• Proposed basic laws of inheritance

• Results were repeatable and reliable

• Formed the foundation for classical genetics

Key Outcomes of Mendel’s Work

🧬 1. Monohybrid Cross:

• Cross between two true-breeding plants differing in one contrasting trait

• Example: Tall (TT) × Dwarf (tt)

• All plants were Tall (Tt)

• Resembled only one parent → Tall = Dominant Trait

• Dwarf trait not seen → Recessive

🌿 F₁ Generation (First Filial):

🔁 F₂ Generation (Self-pollination of F₁ i.e. Tt × Tt):

| Gametes from each Tt parent:
T and t (in equal proportion)

🧮 Punnett Square:

• Genotype Ratio:
  1 TT : 2 Tt : 1 tt (1:2:1)

• Phenotype Ratio:
  3 Tall : 1 Dwarf (3:1)

Dominant trait appears 75% of the time, recessive 25%

F₂ Results:

• No blending: Traits remained distinct, not mixed

• Factors = Genes, passed from parents to offspring

• Alleles: Alternate forms of a gene (e.g., T and t for height)

• Genotype: Genetic makeup (TT, Tt, tt)

• Phenotype: Physical appearance (Tall or Dwarf)

🧠 Key Concepts:

• In heterozygote (Tt) → only T (Tall) is expressed

• Hence, T is dominant, t is recessive

Dominance:

• Cross between dominant phenotype plant (unknown genotype: TT or Tt)
  ×
  recessive plant (tt)

• If offspring all tall → parent is TT

• If 1:1 Tall:Dwarf → parent is Tt

🧪 Test Cross:

In heterozygous condition, one allele masks the expression of the other.

Mendel's Two Laws (from Monohybrid Cross): 1⃣ Law of Dominance

Alleles separate during gamete formation, and each gamete receives only one allele.

2⃣ Law of Segregation

🧮 BONUS: Binomial Representation

(½T + ½t)² = ¼TT + ½Tt + ¼tt → matches F₂ genotype ratio

🌟 LAW OF DOMINANCE (Mendel’s 1st Law)

📘 Definition:

In a heterozygous condition, one allele (factor) expresses itself (dominant), while the other remains hidden (recessive).

🧬 Key Points:

1. ✅ Characters are controlled by discrete units → called factors (now called genes).

2. 🔗 Factors occur in pairs → one from each parent.

3. 💪 In a dissimilar pair (heterozygous) →
   One factor is dominant, the other is recessive.

🌿 Application in Monohybrid Cross:

• F₁ Generation:
  Only the dominant trait appears
  (e.g., Tall in Tt = Tall)

• F₂ Generation:
  Both traits appear in a 3:1 phenotypic ratio

  • 3 Tall (TT, Tt)

  • 1 Dwarf (tt)

🧬 LAW OF SEGREGATION (Mendel’s 2nd Law)

📘 Definition:

During gamete formation, the two alleles of a gene pair segregate (separate) from each other so that each gamete receives only one allele of the pair.

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🔑 Key Points:

1. ⚖ No blending of alleles

   • Both traits reappear in F₂ generation as distinct traits, not mixed.

   • Even if only the dominant trait appears in F₁, recessive shows up again in F₂.

2. 🌱 Gamete Formation:

   • Alleles segregate randomly

   • Each gamete carries only one allele

   • 💡 Example:

     • Homozygous TT → gametes: all T

     • Heterozygous Tt → gametes: T and t (in 1:1 ratio)

3. 🎯 F₂ Generation Outcome:

   • Reappearance of both parental traits (e.g., Tall & Dwarf in 3:1 ratio)

🧠 Conclusion:

🔑Law of Segregation is universal – applies to all sexually reproducing organisms

• Even when a trait is not expressed in F₁, it is not lost, just masked – and segregates out in F₂

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🌸 INCOMPLETE DOMINANCE

📘 Definition:

Incomplete dominance is a type of inheritance in which neither allele is completely dominant over the other, resulting in a blending of traits in the F₁ generation.

🌼 Classic Example: 🔬 Snapdragon (Antirrhinum majus) Flower Colour

• Parental Cross:
  🔴 Red (RR) × ⚪ White (rr)
  ↓
  🟣 F₁ Generation (Rr): Pink (Intermediate phenotype)

• F₂ Generation (Rr × Rr):
  1 Red (RR) : 2 Pink (Rr) : 1 White (rr)
  👉 Genotypic Ratio = Phenotypic Ratio = 1:2:1

🎯 Key Concept:

• R (Red allele) is not completely dominant over r (White).

• So, heterozygote Rr shows an intermediate phenotype (Pink).

• This differs from complete dominance where dominant hides recessive.

🧬 Mechanism Behind Dominance:

• Each gene codes for a product (e.g., enzyme).

• Modified alleles may:

  1. 🔸 Make less efficient enzyme

  2. 🔸 Make non-functional enzyme

  3. 🔸 Make no enzyme at all

• If only one allele is functional, phenotype depends on how much product is made.

• If half the enzyme isn't enough to express full trait → incomplete dominance results.

🧠 Quick Recall:

🧬 CO-DOMINANCE

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📘 Definition:

Co-dominance is a condition where both alleles in a heterozygote are fully expressed, leading to a phenotype that shows both parental traits simultaneously — not blending, but co-expression.

🩸 Classic Example: ABO Blood Groupi

ng

👥 Genotypes & Phenotypes:

🧠 Key Concept:
In IᴬIᴮ, both alleles produce their own sugars, so RBCs have both A and B antigens – no dominance or blending → Co-expression!

🔁 Multiple Alleles

A gene with more than two alleles in the population (but still only two in an individual).

🌟 ABO system has three alleles: Iᴬ, Iᴮ, i → example of multiple allelism.

🌽 Bonus Example: Starch Synthesis in Peas

📊 Summary Table:

Which of the following statements best defines pleiotropy?

A. A gene that is present on multiple chromosomes
B. A gene that controls only one phenotypic trait
C. A single gene that affects multiple unrelated traits
D. Multiple genes that affect a single trait

✅ Correct Answer: C
Explanation: Pleiotropy refers to a single gene influencing multiple phenotypic traits.

🌱 INHERITANCE OF TWO GENES – DIHYBRID CROSS (MENDEL'S 2nd EXPERIMENT)

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🧬 Definition:

When two different traits are studied together in a cross, the inheritance pattern is called a Dihybrid Cross.

🌿 Mendel’s Example Traits:

🌼 Parental Cross:

🌿 F₁ Generation:

• All offspring: RrYy (Round Yellow)

• Phenotype: All round yellow (dominant traits)

• Shows law of dominance.

🌱 F₂ Generation:

Selfing RrYy × RrYy

• Gametes from each: RY, Ry, rY, ry

• Punnett square gives 16 combinations.

🔢 F₂ Phenotypic Ratio (Dihybrid Ratio):

📘 Conclusion:

• Each pair of alleles segregates independently —> Law of Independent Assortment

• Two traits are inherited independently of each other.

🧠 Key Concepts Recap:

• Law of Dominance → F₁ shows dominant trait.

• Law of Segregation → Traits separate during gamete formation.

• Law of Independent Assortment → Traits assort independently in F₂.

🧬 4.3.1 Law of Independent Assortment – Mendel’s 2nd Law

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📜 Statement:

When two pairs of traits are combined in a hybrid, the segregation of one pair of characters is independent of the other pair during gamete formation.

🌱 Mendel’s Dihybrid Cross Example:

🧪 Parental Genotypes

• RRYY (Round, Yellow) × rryy (Wrinkled, Green)
  🔄 Gametes: RY and ry

🌼 F₁ Generation:

• Genotype: RrYy

• Phenotype: All Round Yellow (dominant traits)

🌾 F₂ Generation –

Selfing RrYy × RrYy

Gametes from each parent:
RY, Ry, rY, ry

🧩 Using Punnett Square → 4 × 4 = 16 combinations

🎯 Phenotypic Ratio (Dihybrid Ratio):

🧠 Genotypic Ratio (All 16 Squares):