Question

Case study

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 in male and female. In male it is '44 + XY' and in female 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 homogametic i.e., produces only one type of gamete with '22 + X' chromosomes only. Sometimes an error may occur during meiosis of cell cycle, where the sister chromatids fail to segregate called nondisjunction, leading to the production of abnormal gametes with altered chromosome number. On fertilisation such gametes develop into abnormal individuals.

(a) State what is aneuploidy.

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

(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.

OR

(c) Name a best known and most common autosomal aneuploid abnormality in human and write any two symptoms.

Answer 1

(a) Aneuploidy: Failure of segregation of chromatids during cell division cycle results in the gain or loss of a chromosome (s), called aneuploidy.

(b) If during spermatogenesis, the chromatids of sex chromosomes fail to segregate during meiosis, different types of gametes with altered chromosome produced will be-

(i) 22 + XY

(ii) 22 + O

(c)

  

Person with 44 + XXY karyotype would suffer from Klinefelter's syndrome. Symptoms of Klinefelter's syndrome include –

(i) Tall stature

(ii) Feminine development, e.g., development of breast i.e., Gynaecomastia

(iii) Sterility

OR

(c) Down's syndrome is a best known and most common autosomal aneuploid abnormality in human. Symptoms of Down's Syndrome include -

(i) Short stature

(ii) Small round head

(iii) Furrowed tongue/big and wrinkled tongue

(iv) Partially open mouth

(v) Retarded physical, psychomotor and mental development

(vi) Flat back of head

(vii) Many 'loops' on finger tips

(viii) Palm crease

(ix) Broad flat face

(x) Congenital heart disease