हिंदी
Tamil Nadu Board of Secondary EducationHSC Science Class 12
पाठ्यपुस्तक उत्तर१०९५२
अवधारणा स्पष्टीकरण११३
पाठ्यक्रम

Human Genetic Disorders - Chromosomal Disorders or Abnormalities

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CBSE: Class 12

Key Points: Chromosomal Disorders or Abnormalities

Chromosomal Disorder Chromosomal Abnormality Karyotype Major Features Remarks
Down’s Syndrome Extra copy of chromosome 21 (Trisomy 21) 47, +21 Short stature, small round head, furrowed tongue, partially open mouth, broad palm with single crease, mental and physical retardation Most common autosomal aneuploidy
Klinefelter’s Syndrome Extra X chromosome in males 47, XXY Masculine body with feminine traits (gynecomastia), underdeveloped testes, sterile Sex-chromosome aneuploidy
Turner’s Syndrome Absence of one X chromosome 45, XO Short stature, rudimentary ovaries, absence of secondary sexual characters, sterile female Only monosomy compatible with life
Aneuploidy Gain or loss of one or more chromosomes due to non-disjunction 2n ± 1 Severe developmental abnormalities Includes trisomy and monosomy
Polyploidy Increase in whole set of chromosomes due to failure of cytokinesis 3n, 4n, etc. Common in plants; increases size and vigor Rare and usually lethal in animals

Related QuestionsVIEW ALL [9]

Females with Turners’ syndrome have

What is Down’s syndrome? Give its symptoms and cause. Why is it that the chances of having a child with Down’s syndrome increases if the age of the mother exceeds forty years?

Pataus’ syndrome is also referred to as ____________.

How was it concluded that genes are located on chromosomes?

The chromosome number is fixed for all normal organisms leading to species specification whereas any abnormality in the chromosome number of an organism results into abnormal individuals. For example, in humans, 46 is the fixed number of chromosomes both male and female. In males it is '44 + XY' and in females, it is '44 +XX'. Thus the human male is heterogametic, in other words produces two different types of gametes one with '22 + X' chromosomes and the other with '22 + Y' chromosomes respectively. Human female, on the other hand, is homo gametic i.e. produce only one type of gamete with '22 + X' chromosomes only.

Sometimes an error may occur during the meiosis of the cell cycle, where the sister chromatids fail to segregate called nondisjunction, leading to the production of abnormal gametes with altered chromosome numbers. On fertilisation, such gametes develop into abnormal individuals.

(a) State what is aneuploidy. (1)

(b) If during spermatogenesis, the chromatids of sex chromosomes fail to segregate during meiosis, write only the different types of gametes with altered chromosome numbers that could possibly be produced. (1)

(c) A normal human sperm (22 + Y) fertilises an ovum with karyotype '22 +XX'. Name the disorder the offspring thus produced would suffer from and write any two symptoms of the disorder. (2)

OR

(c) Name the best-known and most common autosomal aneuploid abnormality in humans and write any two symptoms. (2)

Klinefelters’ syndrome is characterized by a karyotype of ____________.

Mention the symptoms of Down's syndrome.

Define aneuploidy. How is it different from polyploidy? Describe the individuals having following chromosomal abnormalities.

  1. Trisomy of 21st Chromosome
  2. XXY
  3. XO

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