PCR, Tandem Repeats, & Genome Variation Flashcards
(10 cards)
What is the relationship between gene number, genome size, and organismal complexity?
There is not a direct correlation. Some simple organisms have large genomes or many genes. Complexity often depends more on gene regulation and non-coding DNA than raw gene number or genome size.
How does PCR (polymerase chain reaction) amplify DNA?
PCR uses cycles of denaturation (heat), annealing (primer binding), and extension (DNA synthesis) to exponentially copy a specific DNA region.
What is a tandem repeat (TR) in genetics?
A tandem repeat is a short DNA sequence repeated back-to-back (e.g., “GATA GATA GATA”). The number of repeats varies between individuals and is a source of genetic variation.
How is TR analysis used in DNA fingerprinting?
PCR amplifies TR regions. Gel electrophoresis separates products by size, allowing comparison of repeat lengths between individuals for identity or diversity analysis.
How do you design PCR primers to amplify a specific DNA region?
Select two short DNA sequences (18–25 bases) that flank the target region:
One forward primer (binds to 5′ end of bottom strand)
One reverse primer (binds to 5′ end of top strand, runs 3′→5′ direction)
How do you predict the size of a PCR product?
Subtract the start position of the forward primer from the end position of the reverse primer (include both primers’ lengths if needed).
What happens if a required PCR component is missing or changed?
No template DNA: No bands produced
No primers: No amplification
Too high annealing temperature: Primers don’t bind → no product
Low dNTPs or Taq polymerase: Weak or incomplete amplification
How do you interpret gel results to detect PCR design errors?
No band: Could indicate missing components, poor primers, or wrong annealing temp
Multiple bands: Non-specific primer binding
Wrong band size: Incorrect primer design or unexpected mutations
How can PCR results reveal the presence or absence of a region in different genomes?
Presence = visible PCR band
Absence = no band (assuming controls work), suggesting deletion or divergence in that region among organisms
How do you interpret TR-based DNA fingerprinting data?
Compare band sizes (repeat lengths) across samples:
Matching profiles = same individual or identical TR loci
Different patterns = different individuals or alleles
Used in forensics, paternity testing, and population genetics
