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Down’s syndrome is caused by trisomy of chromosome 21, leading to developmental and cognitive impairments.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Chromosomal Theory Linkage Recombination Gene Mapping
Down’s syndrome is caused by trisomy of chromosome 21, leading to developmental and cognitive impairments.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Polygenic Inheritance Pleiotropy and Quantitative Inheritance
Down’s syndrome is caused by an extra copy of chromosome 21, not the Y chromosome.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Polygenic Inheritance Pleiotropy and Quantitative Inheritance
Down syndrome most common viable autosomal aneuploidy, frequency about 1 in 700 births rising sharply with maternal age after 35 years due prolonged oocyte arrest. Cytogenetically majority cases free trisomy 21 with 47,XX+21 or 47,XY+21 karyotype showing extra small acrocentric chromosome in metaphase. Phenotype includes characteristic facial appearance upslanting palpebral fissures, single palmar crease, hypotonia, intellectual disability variable, increased risk congenital heart defects, duodenal atresia, early Alzheimer-like pathology by fourth decade. Chromosome 21 smallest autosome contai
Ref: Lewis, Human Genetics, 12th ed., Chapter 9: Down Syndrome Trisomy 21 Phenotype and Karyotype
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