Genetics

Familial Breast Cancer Risk

• Family history of breast cancer increases risk, particularly if close relatives are diagnosed at young ages.
• Direct-to-consumer (DTC) genetic tests, such as those from 23andMe and Ancestry.com, may indicate breast cancer risk but can lack clinical accuracy.
• Negative results from DTC tests do not fully rule out genetic predisposition, especially with familial histories.

The Nuclear Genome

• Human nuclear genome consists of approximately 3.2 billion base pairs and is organized into 23 chromosomes.
• Somatic cells are typically diploid with 22 pairs of autosomes and one pair of sex chromosomes.
• Haploid cells (sperm and oocytes) contain 23 single chromosomes; variation in chromosome number occurs in certain tissues due to genetic syndromes or cancer.
• Karyotyping detects chromosomal abnormalities linked to diseases, while aneuploidy indicates abnormal chromosome counts.
• Telomerase is an enzyme that extends telomeres, prominent in rapidly dividing cells, influencing genetic stability.

Microsatellite DNA

• Unique profiles of microsatellite sequences (2-13 base pair repeats) are distinctive to each individual, aiding in forensic science and paternity testing.
• Microsatellites can expand or contract during replication, contributing to genetic variability among cells.

Transposable Elements

• Three different kinds of transposable elements exist: DNA transposons, retrotransposons, and non-autonomous transposons.
• Retrotransposons move within the genome through an RNA intermediate, emphasizing evolutionary processes.
• Mitochondrial DNA is maternally inherited, crucial for tracing human evolutionary lineage.

The Microbiome

• Composed of microorganisms like bacteria and fungi, the human microbiome has a higher cell count than human cells, weighing 2-5 pounds on average.
• Unique microbial compositions characterize different body parts, influencing health and disease.

Microarray Genotyping

• Utilizes automated techniques with microarrays of DNA fragments to identify genetic sequences by hybridization.
• Commonly employed by DTC testing services, microarrays can also target specific diseases for clinical genetic diagnosis.

Targeted and Gene Panel Sequencing

• Preset gene panels focus on significant genes associated with specific diseases, optimizing resources and data analysis.
• Whole Exome Sequencing (WES) provides insights into protein-coding regions; however, many disease mutations are located outside these regions.

Genome-Wide Association Studies (GWAS)

• GWAS is used to identify genetic associations with diseases by comparing genomic sequences of affected and unaffected individuals.
• Validity relies on comparing subjects from similar ethnic and racial backgrounds to improve relevance and accuracy.

Risk Factors for Breast Cancer

• Key risk factors include being female, advancing age, family history, and specific inherited gene variants (e.g., BRCA1/2).
• Reproductive history, such as early menstruation and late menopause, correlates with prolonged estrogen exposure, potentially increasing cancer risk.

Explore the complexities of familial breast cancer risk and the implications of DTC genetic testing. This quiz covers the structure of the human nuclear genome, chromosome organization, and the significance of chromosomal abnormalities. Test your knowledge on how genetics plays a crucial role in cancer predisposition.