Genetic Disorders – Class 12 Biology

In this videos we are going to Genetic disorders are diseases caused by abnormalities in an individual’s DNA. These can be inherited from parents or caused by mutations. They are categorized into:

1️⃣ Mendelian Disorders (caused by single-gene mutations)
2️⃣ Chromosomal Disorders (caused by abnormalities in chromosomes)


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1️⃣ Mendelian Disorders (Single-Gene Disorders)

These follow Mendel’s Laws of Inheritance and can be dominant or recessive.

(A) Autosomal Recessive Disorders

Require two copies of the defective gene (one from each parent).

Examples:
🔹 Cystic Fibrosis – Thick mucus in lungs, difficulty in breathing.
🔹 Sickle Cell Anemia – Abnormal hemoglobin causes sickle-shaped RBCs.
🔹 Phenylketonuria (PKU) – Lack of enzyme to break down phenylalanine, leading to brain damage.
🔹 Tay-Sachs Disease – Accumulation of fatty substances in the brain, causing nervous system damage.


(B) Autosomal Dominant Disorders

Only one copy of the mutated gene is needed to express the disease.

Examples:
🔹 Huntington’s Disease – Brain degeneration, loss of muscle control.
🔹 Marfan Syndrome – Connective tissue disorder affecting heart, eyes, and bones.


(C) X-Linked Disorders

Genes are located on the X chromosome.

Examples:
🔹 Hemophilia – Blood doesn’t clot properly.
🔹 Color Blindness – Difficulty distinguishing red and green colors.
🔹 Duchenne Muscular Dystrophy – Progressive muscle weakening.



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2️⃣ Chromosomal Disorders

Caused by abnormalities in chromosome number or structure.

(A) Aneuploidy (Change in Chromosome Number)

Occurs due to non-disjunction (failure of chromosomes to separate during meiosis).

🔹 Down Syndrome (Trisomy 21)

Extra chromosome 21 (47 chromosomes instead of 46).

Symptoms: Intellectual disability, short stature, slanted eyes.


🔹 Turner Syndrome (45, XO)

Only one X chromosome (females have 45 chromosomes instead of 46).

Symptoms: Short height, infertility.


🔹 Klinefelter Syndrome (47, XXY)

Males have an extra X chromosome (47 chromosomes).

Symptoms: Tall stature, infertility, breast enlargement.


(B) Structural Chromosomal Disorders

Cri-du-chat Syndrome – Deletion of part of chromosome 5; infants have a "cat-like" cry.

Philadelphia Chromosome – Translocation between chromosomes 9 and 22, linked to leukemia.



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3️⃣ Detection & Treatment

🔍 Genetic Testing Methods:
✅ Karyotyping – Identifies chromosomal abnormalities.
✅ PCR & DNA Sequencing – Detects single-gene mutations.
✅ Amniocentesis – Tests fetal chromosomes during pregnancy.


💊 Possible Treatments:
🔹 Gene Therapy – Corrects defective genes (e.g., SCID treatment).
🔹 CRISPR Gene Editing – Experimental technique for modifying DNA.
🔹 Enzyme Replacement Therapy – Used in metabolic disorders like Gaucher’s disease.

Would you like detailed notes, diagrams, or MCQs for practice? 😊


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