Lecture 7- Application of genetics to human disease

Question 1

what is sickle cell disease?

Answer 1

A disease affecting haemoglobin in the red blood cells.

Question 2

state 4 symptoms of sickle cell disease?

Answer 2

1- Fever
2- Intense pain in joints nd abdomen
3- Sickled red blood cells
4- Anaemia

Question 3

who does sickle cell disease mostly occur in?

Answer 3

in children (many of which die in early childhood)

Question 4

what is the appearance of red blood cells in sickle cell disease?

Answer 4

crescent-like / sickled shape

Question 5

what are the ocular symptoms of sickle cell disease?

Answer 5

• blockage of capillaries largely affecting the retina
• New blood vessels growing on posterior surface of vitreous= vascular fans
• haemorrhage
• dilated blood vessels of conjunctiva
• retinal detachment

Question 6

what is the normal gene for haemoglobin?

Answer 6

Hb (A) Hb(A)

Question 7

what is the gene required for haemoglobin to acquire sickle cell disease?

Answer 7

Hb (S) Hb (S)

Two copies required for the disease

Question 8

what is the gene required for sickle cell trait? Describe the relationship between Hb (A) and Hb (S).

Answer 8

Hb (A) Hb (S)

a less severe form of the disease , but there is no recessive and dominant relation between Hb (A) and Hb (S)

Question 9

How can you diagnose the presence of sickle cell disease early in life?

Answer 9

A sample of blood is placed on a conducting filter

an electric field is applied

the blood moves in response to the field

the blood will move normally from +ve and -ve end of field - symmetrical distribution from the source whereas in sickle cell disease the blood moves more towards the positive pole giving an asymmetrical distribution

Question 10

how can you examine the haemoglobin in sickle cell disease?

Answer 10

• digest protein with various enzymes to break peptide bonds
• peptide fragments separated as the move due to an electric field
• A “fingerprint” of the molecule is obtained

Question 11

in sickle cell disease which haemoglobin chain is affected?

Answer 11

beta chain

Question 12

which amino acid and nucleotide is altered in the haemoglobin chain?

Answer 12

glutamic acid is changed to valine

T is changed to A

Question 13

what is alcaptonuria and state all symptoms?

Answer 13

Adults have a blue black staining affecting the ears

Blue black colouration affecting the ear , sclera, cornea and conjuctiva

degeneration of collagen

urine turns jet black

Question 14

fill in the blanks:

In normal cells, the amino acid _________ is converted by the first enzyme into the intermediate called ___________ ______ and then converted into _________ by the second enzyme which is excreted in ______. However, in alcaptonuria the second enzyme is ________, so accumulation of _________ ______ results in black/ blue coloration of tissues and ______.

Answer 14

Tyrosine

Homogentisic acid (HGA)

urine

defected

urine

Question 15

what is lesch-nyhans syndrome?

Answer 15

• Caused by gene on X-chromosme
• Affects males and passed from mothers to sons
• severe mental retardation
• self-mutilation

Question 16

which gene is responsible for lesch-nyhans syndrome?

Answer 16

HPRT gene