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UPPCS Biology Gap Sheet: Chromosomes, Genetics and Biotechnology.
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First, the concept
Chromosomes carry genes, and alleles are versions of a gene. A dominant allele can be expressed in a heterozygote; a recessive condition usually needs two recessive alleles on autosomes.
Sex-linked inheritance follows the location of the gene. A male has only one X chromosome, so an X-linked recessive allele can be expressed directly. Biotechnology changes or measures genetic material rather than merely selecting visible traits.
✅ Already asked (20)
Chromosomes and inheritance
- Human chromosome number · Most body cells have 46 chromosomes; gametes have 23.
- Chromatin · Eukaryotic DNA is packed with histone and other proteins.
- DNA double helix · Watson and Crick proposed the model in 1953 using evidence including X-ray data.
- Base pairing · DNA: A–T and G–C; RNA uses U instead of T.
- Mendel's pea experiments · Garden pea supported the laws of segregation and independent assortment.
- Independent assortment limit · Closely linked genes need not assort independently.
- ABO codominance · A and B alleles are codominant; O is recessive to both.
- Y chromosome and SRY · SRY normally initiates testis development; sex development has biological exceptions.
Inherited disorders
- Red-green colour blindness · Usually X-linked recessive; not the same as vitamin-A night blindness.
- Haemophilia A and B · Usually X-linked recessive; factor VIII or IX deficiency affects clotting.
- Thalassaemia · Inherited reduction in globin-chain production; a haemoglobin disorder.
- Sickle-cell disease · Usually autosomal recessive; abnormal beta-globin alters red-cell shape.
- Albinism · Reduced or absent melanin production; common forms are autosomal recessive.
- Turner syndrome · Classic karyotype is 45,X; affects females.
- Down syndrome · Usually trisomy 21; an extra chromosome, not a single-gene disorder.
- Klinefelter syndrome · Common karyotype 47,XXY; affects males.
Tools and applications
- Amniocentesis · Samples amniotic fluid for selected fetal genetic tests.
- Bt crops · Carry selected Bacillus thuringiensis genes for insect resistance.
- Gene therapy · Adds or modifies genetic material to treat selected diseases.
- DNA fingerprinting · Compares variable DNA regions; ordinary identical twins share near-identical profiles.
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⚠️ Amniocentesis can diagnose fetal disorders; prenatal sex determination is prohibited in India.
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