(1) people who are asymptomatic, but carry a gene that increases the probability that they will develop the disease.

(2) individuals who are heterozygotes (carriers) for some recessive or X-linked genetic condition, but who remain asymptomatic

(3) individuals with one or more genetic polymorphisms that are not known to cause any medical condition

(4) imediate relatives of individuals with known or presumed genetic diseases.
 

People in category 1
 

(a) individuals with conditions that can be treated before the symptoms become manifest, so that the disease is not disabling (PKU)

(b) individuals whi in the future will be affected by unteatable and fatal conditions (Huntington's disease)

(c) individuals who have diseases that vary in the severity or the effectiveness of the treatment

(d) individuals who have genes that do not necessary lead to disease, but could increase the probability of a disease (cancer, diabetes, heart disease)

(e) individuals whio have genes that make them suscepatable to envirnmental factors or toxins.
 

2. Male and female carriers of autosomal recessive traits, as well as women who are carriers of X-linked diseases.
 

3. Individuals with benign genetic polymorphisms (e.g. blood group polymorphisms)
 
 
 

Think about groupings for points 2 and 3
 
 
 
 

TYPICAL PATHWAYS -selection
 

	ATP
	^
	dADP
	^
	AMP	<---ARPT **8 aza A **6 diaminopurine	<-------<---ADENINE + PRPP
	^
	adenosuccinate
	^
de novo pathway	^ (arrow up)
PURINE---11 ENZYMES + PRPP BIOSYNTHESIS	-->IMP <--	<...HGPRT- **8 AZA A	<---HYPOXANTHINE
**AMINOPTERIN	v (arrow down)
	v
	XMP
	v
	GMP	<-----HGPRT ** 8 AZA A OR 6 THIOGUANINE	<---GUANINE + PRPP
	v
	GDP
	v
	dGTP

NOTES: 1) Any of the drugs** can kill normal cells because they enter the pathways as analogues of a normal component

2) 8 AZA A or 6-Thioguanine (examples) cannot enter the pool IF HGPRT is absent
 

=======================
 

A few notes and diagrams concerning HAT
 

HAT MEDIA contains hypoxanthine, aminopterin and thymidine
 

dUMP------------------->	dTMP-->--->--->	DNA
*AMINOPTERIN	^
	TK

                                                                                                    ^
                                                                                                    ^
                                                                                                    THYMIDINE
 
 
 

A normal cell will grow in the presence of aminopterin IF thymidine is present

Remember that hypoxanthine has to be present for IMP synthesis in the presence of the an aminopterin block
 

In conditions of NO SELECTION, thymidine kinase is not necessary because it could be formed from dUMP
 

NOTE: TK- cells cannot use thymidine or BUDR