4. week 5 SNPs summary

Single Nucleotide Polymorphisms (SNPs)

  • Changes in single base sequences among individuals.

  • Do not alter DNA length.

  • Most common genetic variation in humans (approx. one SNP every 300 bp; >10 million SNPs total).

  • Frequent in non-coding regions but can occur within genes, potentially leading to diseases (e.g., Cystic Fibrosis).

SNP Distribution

  • Not evenly distributed across chromosomes; regions of high and low SNP density exist.

Causes of SNPs

  • Result from replication errors or DNA damage.

  • SNPs in gametes can be inherited by offspring.

Identifying SNPs

  • Involves sequencing DNA from many individuals and aligning sequence reads to find variations.

SNP Alleles

  • Typically two variants (original and new), with rare instances of four.

  • Alleles identified using rs numbers in databases; major allele >1% frequency, minor allele <1%.

SNP Inheritance

  • Follow Mendelian inheritance, no gender bias unless on sex chromosomes.

SNP Haplotypes

  • Collections of SNPs inherited together; can define ethnic groups.

  • Used in forensic identification (case studies cited).

DNA Sequencing Methods

  • Essential for pinpointing SNPs; evolved significantly since the 1970s (improvements include fluorescence and capillary electrophoresis).

Sanger Sequencing

  • Amplifies target DNA, utilizes modified nucleotides (ddNTPs) to stop DNA extension, leading to varying fragment lengths.

  • Results visualized using electrophoresis; advancements have streamlined the process (single tube reactions, fluorescent dyes).

Enhancements in Sequencing Technology

  • Transitioned from multiple reactions to a single one, improving accuracy and speed in SNP identification.