Detection of Hereditary Breast Cancer Breast Cancer Genes

Detection of Hereditary Breast Cancer

Breast Cancer Genes • Two genes associated with inheritance of breast cancer – Breast cancer gene 1 (BRCA 1) – Chromosome 17 – BRCA 2 – Chromosome 13 • When normal… – Both are tumor suppressor genes • Repair damage and prevent cancer cells from forming • When mutated… – Lead to breast or ovarian cancer

BRCA 1 and BRCA 2 • 5 to 10% of all breast cancers are because of these genes • Women… – 12% chance of developing breast cancer in lifetime • Goes up to 85% if said woman has mutated BRCA 1 or 2 • If male has BRCA 2 mutation – 1 in 10 ratio of getting breast cancer (100, 000 jump)

Family Members • Judy is worried!!!!! • Jennifer has DNA sequencing… – Jennifer had breast cancer • Test positive of BRCA 2 (negative for BRCA 1) – Laura • Tests positive for same mutation as Jennifer

BRCA 2 • We will be looking at BRCA 2 – Contains 80, 000 nucleotides • 600 mutations associated with BRCA 2 – Most cause increased incidence of breast cancer (not all) • Most of these mutations are insertion or deletion

Marker Analysis (Haplotyping) • Due to expense of DNA sequencing… – We will use marker analysis to test Jennifer and Diana • Marker analysis… – Genetic test – Gene mutation is analyzed using a genetic marker • Instead of analyzing genet itself • Genetic marker: short sequence of DNA associated with a particular gene or trait with a known location on a chromosome

Short Tandem Repeats • Genetic markers used in marker analysis are short DNA sequences – Also called microsatellites • STR = region of DNA composed of a short sequence of nucleotides repeated many times. – Number of repeated STRs varies from person to person • Different number of repeats = different alleles • Most occur in introns (non-coding DNA) – Do not affect gene function

STR for BRCA 2 • Location = chromosome 13 • STR analysis for this lab – It is on 13, next to BRCA 2 gene

Gel Electrophoresis • Different STRs have different repeats… – Gel will separate alleles based on number of repeats • More repeats travels less • Less repeats travels more

Loading Samples • • 5 u. L: 130 Volts for 30 minutes Lane #1: DNA Size Markers Lane #2: Helen’s DNA Lane #3: Harold’s DNA Lane #4: Susan’s DNA Lane #5: Adam’s DNA Lane #6: Negative Control

Determining Size of DNA Fragment • Using a ruler – Measure (ON EACH BAND!!!!) • Distance of DNA fragment from origin (gel well) • Distance from the origin (gel well) to the tracking dye

Calculate the Rf value Distance the DNA fragment has migrated from the origin (gel well) Rf = Distance from the origin (gel well) to the reference point (tracking dye)

DNA Size Markers Fragment Length in Base Pairs Distance Migrated (mm) A Distance to Reference Point (mm) B Rf A ÷ B Fragment 1 1353 Fragment 2 1078 Fragment 3 872 Fragment 4 603 Fragment 5 310 Fragment 6 281 Fragment 7 234 Fragment 8 194

DNA Sample: Fragment: Distance Migrated (mm) A Distance to Reference Point (mm) B A ÷ B Diana Fragment 1 Fragment 2 Jennifer Laura Judy Rf

DNA Sample: Fragment Length (in base pairs) Allele Present: Diana Fragment 1 Fragment 2 Jennifer Laura Judy

Fragment Length in Base Pairs: Allele: 200 Allele 1 300 Allele 2 400 Allele 3 500 Allele 4 600 Allele 5 700 Allele 6 800 Allele 7 900 Allele 8 1000 Allele 9

Questions 1. Which allele is associated with the BRCA 2 mutation? Explain your answer. 2. Which family members have the BRCA 2 mutation? Explain your answer. 3. Explain whether you think Judy’s family occurrences of breast and ovarian cancers are sporadic, hereditary, or familial. 4. Is Judy a good candidate for BRCA 1 or BRCA 2 genetic testing? Explain your answer.