GENETIC DISORDERS

Q. Write an account of thalassemia -

Ans. - (1) It is characterised by reduced synthesis of or chains pf hemoglobin.

(2) Hence, it shows two types as thalassemia or B- thalassemia.

(3) It was discovered by Coley (1925) hence it is also known as Cooley’s    anemia or thalassemia Major.

(4) Hemoglobin is a conjugated protein consisting of A and B chains, each chain with a and b subunits.

(5) The decreased synthesis is of Hb A chain.

(6) The a-globin chain is coded by a gene on chromosome 16 and the gene for b-globin chain is located on chromosome 11.

(7) It results in deficiency of one chain and the relative excess of other chain.

(8) Clinical symptoms are occurrence of anemia inability to synthesize Hb, Jaundice, variation in size and shape of RBC’.

(9) Massive blood transfusion is needed i.e. transfusion one or two times the patients normal blood volume.

(10) Thalassemia is a quantitative abnormality of polypeptide globin chain synthesis.

(11) In normal adult, this is equivalent to 10-20 units.

Q. Write a note of Down’s syndrome with its symptoms.

    Ans.:- 1) Down’s syndrome is caused due to aneuploidy.

     2) The syndrome was described by John Langdon Down.

     3) It is due to trisomy at 21st chromosome due to which the genotype shows (46 + 1 =47)

     4) An extra chromosome number 21 (from group G). It results in 3 copies of 21st chromosome instead homologous pair.

     5) It occurs due to failure of separation of chromosome or non-disjunction during meiosis.

     6) It is due to trisomy represented by (2n + 1)

     7) The different symptoms are as follows:

     a) Typical facial features with a fold of skin (epicanthal fold skin) over the inner corner of eye. It results in downward slanting of eyelids.

     b) Typical flat face, rounded flat nose, protruding tongue with open mouth.

     c) Mental retardation.

     d) Poor skeletal development, short stature and relatively small skull and palate is arched.

     e) Flat hand with characteristic crease which runs all the way across the palm. (Simian crease)

     Q.: Write a note on Turner’s syndrome?

    Ans.:- 1) Turner’s syndrome is referred to as X - monosomy

     2) It develops due to non-disjunction during meiosis of either male or female.

     3) Theory suggests that equal number of klinefelter or Turner’s syndrome individual should born but the case or actual results are different.

     4) Turner syndrome is fatal in early pregnancy.

     5) Person suffering from Turners syndrome shows 45 chromosomes with only one sex chromosomes (x). The genotype can be represented as (44 + XO.)

     6) The different symptoms are

     a) The phenotype in these patients is female

     b) Short stature, webbing of neck, low posterior hair line.

     c) Under developed secondary sexual character or no development at all.

     d) Abnormal intelligence, cardiovascular problems.

     e) 44 + YO is male turners syndrome; but it never occurs in nature.

Q. Write a note on Klinfelter’s syndrome.

Ans.:   1) The syndrome was discovered by Klinefelter in 1942.

2) The syndrome is due to trisomy of X - chromosome.

3) It is formed by union of an abnormal XX egg and normal Y sperm or normal X egg and abnormal XY - sperm.

4) The individual has 47 chromosomes (44 + XXY)

5) Such persons are sterile male or feminized males.

6) The different symptoms are as under:

a) Undeveloped testis

b) Mental retardation

c) Female like sparse body hair and knock knees, long limbs.

d) Feminine pitched voice and enlarged breast showing gynecomastia.

7) More the X - chromosome, greater will be the mental defect.

8) In this syndrome, level of FSH is more than the usual FSH level in males.