sickle cell anameia,Colour blindness

Sickle cell Anameia 

Sickle cell anameia is a hereditary disease , It is an autonomic recessive trait .The blood of effected individual has a reduced capacity of delivering oxygen to the tissues. 

Cause of sickle cell anameia

This disease is named because the red blood cells (RBCs) of the affected person have sickle-like shape instead of biconcave structure. 

Development of the Sickle cell Anameia

 The blood of a normal human contains blood protein "haemoglobin" which gives it red colour. This protein is responsible for oxygen supply to all body tissues. RBCs with sickle cell haemoglobin are biconcave in shape which can easily pass through the capillaries. 
Whereas RBCs with sickle cell heamoglobin appear normal as long as oxygen is present in sufficient quantity. As the oxygen level decreases when blood leaves tissues after supplying oxygen (02), this haemoglobin forms insoluble fibrous strand. These strands change the shape of RBCs into long sickles. These sickle cells cannot pass through narrow capillaries so block blood capillaries. The tissues also do not get oxygen. Sickle cells may rupture and cause the anaemia (lack of red blood cells). 

Normal Haemoglobin and Sickle Cell haemoglobin: 

 Haemoglobin is a large protein. It has four chains of amino acids, two alpha (a) chains and two beta (B) chains. In both cases alpha chains are same but only a single amino acid is different in beta chains. The amino acid "Glutamic acid" at 6th position is mutat.

 Mutation which cause Sickle cell Anameia

 The normal haemoglobin allele is HbA. The DNA triplet (three bases form one codon to form one protein) of HbA gene encoding for glutamic acid is CTT. A point mutation changes just the middle base of the triplet from T to A. As it becomes CAT, a new allele HbS emerges. CAT encodes for valine. So, the allele for sickle-cell haemoglobin is HbS. 

Location of Genes for Haemoglobin: 

 The alleles for haemoglobin are present on chromosome Number:one Human chromosome 2-with linked genes of sickle cell anaemia and albinism. 

Inheritance of Sickle-Cell: 

The individuals homozygous for normal haemoglobin are HbA/HbA. They do not have the disease. Homozygotes for sickle-cell allele HbS/HbS have the disease. Heterozygotes HbA/HbS are called sickle-cell carriers.
 The carriers show no symptoms of the disease under normal circumstances. 
Only 1% of their RBCs, become sickle shaped. If a normal woman HbA/HbA married to a sickle cell anaemic man HbA/HbS, all their children will be carrier (HbA/HbS). 

 Colour-blindness 

 Colour-blindness is a hereditary disease. Colour­blind person cannot distinguish red from green. 

Colour blindness

 

 

 

 

 

 

 

Causes of colour blindness

The cause for the lack of sense of distinction between colours is the absence of red and green sensitive cone cells in the retina of eyes. Detail of Genes: The gene for norma! trait is "C" and gene for colour blindness is "c". Inheritance of Disease: If a colour-blind man marries a normal woman , he will pass gene for this trait to all of his daughters through his X-chromosome. 
He cannot pass this 'c' recessive gene to his sons because sons receive only "Y" chromosome from him. His every daughter also receives another X but with the normal dominant allele from her mother. 
She will phenotypically normal but heterozygous and a carrier for this recessive gene, When such carrier lady marries a normal man, she will pass this trait of her father to that half of her sons who inherit grandfather's X from her. The single recessive allele for colour-blindness expresses successfully in a hemizygous son because his Y-chromosome does not carry its counter part. Half of her sons will be normal as they inherit grandfather's X with normal gene. Half of her daughters with both normal X will be normal, but half of her daughters will be carrier like their mother. 
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