Question - Answers
I. Very Short Answer Type Questions
1. What is Kline felters syndrome?
Ans: a. Karyotype of Klinefelter's syndrome is AA + XXY (44 + XXY = 47)
b. It is an example of trisomy.
c. These are males, Barr body positive and are characterised by hypogonadism, reduced fertility, enlarged breasts, rounded hips etc.
2. What is Down Syndrome?
Ans: a. Down syndrome is an example of trisomy with an extra chromosome No. 21 [44 + XX, 21st chromosome = 47]
b. The affected individuals are characterised by short stature with round head, furrowed tongue, partially open mouth, retardation of physical, physchomotor and mental development etc.
II. Long Answer Type Questions
1. Write an essay on genetic disorders.
Ans: Due to changes in gene:
I. Haemophilia (Bleeders disease)
Haemophilia - A (due to lack of factor VIII) and Haemophilia - B (due to lack of factor IX) are X - linked disorders due to recessive gene(s). Haemophilia - C (due to lack of factor XI) is an autosomal disorder.
In haemophilia, in the affected person, the blood does not clot. Even for a small wound, large amount of blood loss occur.
Haemophilia A and B are inherited to next generations in a Crisscross manner.
Haemophilia (A & B) is more common in Males than that of females, because in Males, one X - linked recessive gene is sufficient to express the disorder. Whereas in female, two X-linked recessive genes are required to express. Some females act as asymptomatic carriers of this recessive gene.
Queen Victoria was a carrier of this disorder.
II. Colour blindness
Colour blindness is an X - linked disorder due to recessive gene(s).
In a person suffering from colour blindness, the cones in retina are not properly formed. Hence, he is unable to detect different colours.
Colour blindness is of three types
a. Protanopia - Red colour blindness
b. Deuteranopia - Green colour blindness
c. Tritanopia - Blue colour blindness.
Tritanopia is resulted due to recessive gene in autosome.
Inheritance of colour blindness is similar to that of haemophilia.
In Ishihara colour test, which consists of a series of pictures of coloured spots - used to diagnose red-green colour blindness.
III. Phenylketonuria
Phenylketonuria is an autosomal recessive metabolic genetic disorder resulted due to a mutation in the gene for production of phenylaniline hydroxylase located in chromosome 12.
It was discovered by A.Folling.
In the affected individual the enzyme phenylaniline hydroxylase is not produced and as a result phenylaniline is not converted into tyrosine.
As a result, phenylaniline accumulates and is converted into phenyl pyruvate and other derivatives. Accumulation of these substances in brain causes mental retardation.
IV. Thalassemia
It is an autosomal disorder of blood due to recessive gene or deletion of a segment of chromosome.
This disorder is characterised by excessive distruction of red blood cells due to abnormal haemoglobin.
In affected person, either alpha or beta globin chain is defective and thus abnormal haemoglobin is formed. The persons suffer from anaemia.
V. Sickle cell anaemia:
It is a genetic disorder of blood due to recessive gene of autosome.
In affected individuals abnormal haemoglobin is formed due to replacement of glutamic acid (in sixth position) by valine. As a result, RBC acquires sickle shape. They may clump and clog in smaller blood vessels, often leading to other symptoms.
This disorder is controlled by a single pair of alleles, HbA and Hbs found in chromosome -11.
VI. Cystic Fibrosis
It is an autosomal disorder due to recessive gene in chrosome -7.
In the affected individuals, sweat contains more sodium and chloride and increased resorption of sodium and water from respiratory epithelium.
The extra cellular chloride causes mucus that coats certain cells to become more viscous and sticky. It causes complications in lungs, pancreas- gastro intestinal tract etc., these complications generally cause death by the age of five.
Due to changes number and structure of chromosomes:
1. Euploidy - Changes in number of sets of chromosomes e.g.: Triploidy, Polyploidy
2. Aneuploidy - Changes in number of chromosomes
a. Monosomy - 2x - 1 e.g. Man: 46 - 1 = 45
b. Trisomy - 2x + 1 e.g. Man: 46 + 1 = 47
c. Tetrasomy - 2x + 2 e.g. Man: 46 + 2 = 48
d. Nullisomy - 2x - 2 e.g. Man: 46 - 2 = 44
3. Changes in number of chromosomes is due to non disjunction.
A. Allosomal disorders
1. Turner's Syndrome:
a. Karyotype of Turner's syndrome is AA + XO (44 + X = 45)
b. It is an example for monosomy.
c. These are females, Barr body negative and are characterised by short stature, gonadal dysgenesis, webbed neck, broad shield like chest etc.
2. Klinefelter's Syndrome:
a. Karyotype of Klinefelter's syndrome is AA + XXY (44 + XXY = 47)
b. It is an example of trisomy.
c. These are Males, Barr body positive and are characterised by hypogonadism, reduced fertility, enlarged breasts, rounded hips etc.
B. Autosomal disorders
1. Down Syndrome:
a. Down Syndrome is an example of trisomy with an extra chromosome No. 21 [44 + XX, 21st chromosome = 47]
b. The affected individuals are characterised by short stature with round head, furrowed tongue, partially open mouth, retardation of physical, physchomotor and mental development etc.
2. Edwards Syndrome
a. Edwards syndrome is an example of trisomy with an extra – chromosome No. 18 [44 + X, 18th Chromosome = 47]
b. It is more prevalent in the female offspring. Most of the individuals die during foetal stage. Survived infants suffer from serious defects and live for short span.
3. Patau Syndrome:
a. Patau Syndrome is an example of trisomy with an extra chromosome No. 13 (44 + XX, 13th chromosome = 47]
b. Indviduals with trisomy of 13th chromosome have heart and kidney defects; brain/spinal cord abnormalities; small/poorly developed eyes, cleft palate etc., usually they die in first few weeks.
4. Cri-du-Chat Syndrome:
a. It is due to partial deletion of short arm of chromosome 5 and is described as 5P monosomy. Karyotype is 44 + XX, 5P.
b. The affected children cry like cat due to problems in larynx and nervous system and are mentally retarded. They have small head and die in infancy.
