Genetic Markers Flashcards
T or F: phenotypic variation based on alleles of a gene is the only type of variation between individuals
false! it’s just one type of variation
T or F: much of the sequence variation in the human genome does not affect our phenotype
true
What can be used as a marker to map the location of a gene?
sequence variation
Describe genetic (molecular) markers
polymorphic DNA sequences used to map the location of a gene
Where do genetic markers typically exist in the genome? Where else are they sometimes found?
typically in noncoding regions
sometimes within a gene
What do genetic markers involve?
single nucleotide polymorphisms (SNPs)
restriction fragment length polymorphisms (RFLPs)
Which type of genetic marker is more commonly used?
SNPs
When do SNPs occur?
When one base pair is substituted by another base pair
ex.
A T C C G A C
T A G G C T G
A T C C G G C
T A G G C C G
Approximately how many SNPs exist in the human genome?
~3.3 million
Where are some SNPs located?
within a restriction enzyme recognition sequence
What is a consequence of an SNP in a restriction enzyme recognition sequence?
a single nucleotide change within a restriction enzyme recognition sequence destroys the restriction site and causes a RFLP
Describe RFLPs
Restriction Fragment Length Polymorphisms form when an SNP causes a single nucleotide change within a restriction enzyme recognition sequence and destroys the restriction site
ie., they are changes in DNA sequence
How are RFLPs detected?
by DNA-cutting enzymes (restriction enzymes, specifically restriction endonucleases)
What are the pieces of DNA that result from restriction enzymes cutting?
restriction fragments
How do you know if there’s a restriction site present?
2 smaller fragments are created when the region is cut with a restriction enzyme
How do you know if there’s no restriction site present?
one larger fragment is created when the region is cut with a restriction enzyme
Why are DNA (restriction) fragments different lengths?
because of the single nucleotide difference in the DNA sequence (SNP)
On an agarose gel, how would DNA (restriction) fragments differ?
they would have different band sizes
What purpose do genetic markers serve?
they can be used to trace the inheritance of disease-causing alleles
What can be determined by a genetic marker being within a gene?
the presence of the marker will indicate which allele a person has
What is there risk of if a genetic marker is near a gene?
misdiagnosis due to crossovers
How can the probability of misdiagnosis be determined?
knowing how far the genetic marker is from the gene
What must first be determined before using a genetic marker to trace the inheritance of a disease-causing allele?
the arrangement of the genetic marker and disease-causing allele
ie., which version of the genetic marker is linked to the disease-causing allele
What does it mean if an SNP disrupts a restriction enzyme site on the same chromosome as the recessive allele?
the presence of the restriction enzyme site can be used as a genetic marker for the presence of the dominant allele
What can cause a misdiagnosis if the disease-causing gene and the genetic marker are on the same chromosome?
if crossover occurs during meiosis
