Seminar 18: Genetic linkage & mapping Flashcards
(13 cards)
What is the ratio observed in a DIHYBRID cross when each loci has a phenotype DOMINANT over the other?
9 (A_, B_) : 3 (A_, bb) : 3 (aa, B_) : 1 (aa, bb)
What is the ratio observed in a test cross (dihybrid x homo recessive) when each loci has a phenotype completely dominant over the other?
1 (Aa, Bb) : 1 (Aa, bb) : 1 (aa, Bb) : 1 (aa, bb)
What determines if 2 genes are linked or unlinked?
- Genes on the SAME chromosome; AND
- Genes are CLOSE TOGETHER
What aspect of genes influences the chances of recombination?
PROXIMITY
When are genes considered genetically UNLINKED?
When recombination freq = 50%
PARENTAL ARRANGEMENT of alleles
alleles that occur together one the SAME chromosome in the parent
RECOMBINANT ARRANGEMENT of alleles
alleles that occur together in the progeny after crossing over occurs
Why is the parental arrangement of alleles observed more freq for LINKED loci?
Genes on the same chromosome which are close together (linked) are less likely to be separated during crossing over in meiosis, resulting in the higher frequency.
MAP distance/recombination frequency formula
RF = # of progeny w/ recombinant arrangement / total # of offspring
(x100 for % value)
CIS ARRANGEMENT (parental alleles)
wild type alleles on same chromosome, both mutant on the other
TRANS ARRANGEMENT (parental alleles)
wild type allele & mutant type on same chromosome & vice versa
How to determine Cis & Trans if the wild type allele is UNKNOWN?
refer to the dominant & recessive & their placement
How to distinguish b/w the cis & trans arrangement of alleles in a test cross?
Use the freq of different allele arrangements observed in the progeny to determine
- If # of AB & ab»_space; # Ab & aB, parental allele is in the CIS arrangement
