Gene Linkage
What does it mean for two genes to be linked?
they are located close to one another and are inherited together
What type of cross is used to identify linkage?
testcross (ex: AaBbCc x aabbcc)
How is COC calculated?
observed double crossovers / expected double crossovers
What does SNP stand for?
Single Nucleotide Polymorphism
What does GWAS stand for?
Genome-Wide Association Study
Which principle does gene linkage violate?
independent assortment
How can you identify the parental and recombinant phenotypes?
parentals are most common and recombinants are least common
How is interference calculated?
1 - COC
What is a SNP?
a change in one DNA base at a specific nucleotide position
What is GWAS used for?
to compare SNP frequencies between groups; looks for associations between SNPs and traits
Do linked genes have a high or low recombination frequency?
low, because they are located close to one another
What are the units for map distance?
centiMorgans (cM)
What does a COC equal to 1 mean?
no interference
How often do SNPs occur in the humans?
roughly every 300 nucleotides (about 3 billion total nucleotides in human genome)
Why is GWAS important?
search for cause of traits; risk prediction and prevention strategies
Can genes with a recombination frequency of 75% still be linked?
no; linked genes have a recombination frequency less than 50%
What is the recombination frequency for 2 genes 18 cM apart?
18% recombination frequency
What does a COC less than 1 mean?
positive interference
What is the effect of SNPs?
most have no functional effect, but some may affect protein function or gene regulation
What is a candidate gene?
located near an SNP; suspected to be related to a trait or disease
What is linkage disequilibrium?
when genes are linked
In a 3-gene cross, parental phenotypes are Abc and aBC, and double crossover phenotypes are abC and ABc. Which gene is in the middle?
gene B
What is positive interference?
one crossover can reduce the chance of a second crossover occurring in the same region
Why are SNPs useful?
they act as genetic markers
True or False: a SNP occurring commonly with a disease must be causing that disease
false; correlation does not equal causation