Johnny Johnny presents to the doctor with flu-like symptoms This is his 5 th visit in 3 months He has suffered from a variety of illnesses and doctors begin to suspect an immune deficiency Johnny is referred to a specialist

Genetic Testing A variety of genetic disorders can cause immune deficiency Johnny’s DNA is sampled for analysis by the lab specialist DNA sequencing is performed to look at Johnny’s genetic code for abnormalities

Background - DNA DNA sequences consist of a series of four nucleotides A – Adenine C – Cytosine G – Guanine T – Thymine Example: TACGTACTGTAAATC

Background - Transcription A DNA sequence is transcribed into RNA which can exit the nucleus to produce protein Complementary, antiparallel transcript is produced: DNA: TACGTACTGTAAATC RNA: AUGCAUGACAUUUAG Uracil(U) replaces Thymine (T)

Background - Translation RNA is translated into protein A series of three bases (codon) produces an amino acid RNA: AUGCAUGACAUUUAG Prot: MetHisAspIleStop AUG translates to Methionine CAU translates to Histidine GAC translate to Aspartic Acid AUU translates to Isoleucine UAG is a Stop Codon

Background - Variation All humans have nearly identical DNA sequences There is minor variation that accounts for differences Certain sequences in the DNA code for important proteins If an individual has a mutation in such a sequence, the important protein may not function properly for that person

What does this have to do with Johnny? The doctors suspect that Johnny may have a mutation in a gene that is important for immune response Such a mutation would account for his frequent illnesses There are databases of genetic sequences that are important for immune function Johnny’s DNA can be searched against these databases

Hands On “Searching Johnny’s DNA Sequences” handout – Follow the directions given in the handout