Chapter 14: Genetic Mapping in Eukaryotes Flashcards
Syntenic?
genes that are on the same chromosome
Linked genes?
- genes on the same chromosome that do not seem to assort independently
-loci that are on the same chromosome - inherited together and do not assort independently
- these genes belong to a linkage group
#linkage groups = # chromosomes
Genetic recombination?
the process by which recombinants are produced ( progeny showing non parental combinations of alleles)
Genetic recombination
L> An exchange event between?
L>reshuffling of?
homologous chromosomes
- alleles
L> daugther chromosomes carry combos of alleles not present in parental chromosomes …aka recombinants
Genetic recombination:
Parentals?
- progeny showing parental combination of alleles…aka non-recombinants
Genetic recombination:
-recombinants?
- progeny showing non-parental combination of alleles …aka non-parentals
- crossing over occurs here
L> two homologous chromosomes line up…
chromatids…breakage and crossing over occurs…reunion: exchange is complete…recombinants have formed
Hz(frequency) of recombination:
-The Hz of crossing over between two linked genes is ?
proportional to their location on the chromosome
L> the closer the genes are the less likely there is going to be any crossing over…the farther away they are the more crossing over will occur in that region.
Hz(frequency) of recombination:
-interlocus distance?
the percentage of recombinant offspring produced between two loci and is defined as the interlocus distance
Hz(frequency) of recombination:
- 2% recombination = what in map units or centimorgans?
- 2 map units (mu)
- 2 centimorgans (cM)
- *0.002 frequency of recombination
Linkage ratio?
if two linked loci are far enough apart the # of recombinants will be approximately 50%
- there would be a 1:1:1:1 ratio for all four phonos
Are the loci involved in linked genes different or similar to those seen in unlinked genes?
L> these loci are indistinguishable from unlinked genes
Linked Autosomal Genes
1. Cross wild-type parent with non wild type parent.
a+b+/a+b+ x ab/ab
F1: a+b/ab
Linked autosomal genes:
2. Cross a+b+/ab x ab/ab (test cross)
Parental progeny:
a+b+/ab (wild type)…. ab/ab
Recombinant progent:
a+b/ab ab+/ab
What is the formula for map distance?
map distance = (# recombinant progeny/total # progeny) x 100
Nomenclature for synteny:
double heterozygote for w and m alleles, label if they are trans or cis!
- w+m+/wm
- w+m/wm+
- cis ( when two dominant alleles are on one homolog and the two recessive mutant alleles are on the other homolog…aka coupling)
- trans ( each homolog carries the dominant allele of one gene and the mutant allele of the other gene, called repulsion)
- crossing over of cis loci = w+m and wm+ recombinants
- crossing over of trans loci= w+m+ and wm recombinants
Order of linked genes:
- Explain the three point test cross approach!
- tripe heterozygote crossed with a triple homozygote recessive
- note the phenotypic classes seen in progeny
L> 2 ^n = phenotypic classes - single and double crossovers to consider
Order of linked genes:
- Explain the three point test cross approach!
- tripe heterozygote crossed with a triple homozygote recessive
- note the phenotypic classes seen in progeny
L> 2 ^n = phenotypic classes - single and double crossovers to consider
Recombination Hz for linked genes:
- whats the formula?
(Single cross over region (w+x) + double cross over region (#+#)/ total progeny )100
**this also = map distance
Recombination Hz for linked genes:
- whats the formula?
(Single cross over region (w+x) + double cross over region (#+#)/ total progeny )100
**this also = map distance
Whats the formula for the total map distance when examining recombination Hz for linked genes?
(single crossover region (w+x) + double crossover (#+#) + single crossover region (y+z) + double crossover (#+#)/ number of progeny)100
Whats the formula for the total map distance when examining recombination Hz for linked genes?
(single crossover region (w+x) + double crossover (#+#) + single crossover region (y+z) + double crossover (#+#)/ number of progeny)100
Interference:
- what is this expressed as?
- what is interference?
L>underestimation of what?
- expressed as coefficient of coincidence
- when one crossover event interferes with a second crossover event
- an underestimation of the number of double crossovers
Interference:
- what is this expressed as?
- what is interference?
L>underestimation of what?
- expressed as coefficient of coincidence
- when one crossover event interferes with a second crossover event
- an underestimation of the number of double crossovers
Formula for interference? (cc)
cc= observed double crossover Hz/ expected double crossover Hz
….Interference = 1-cc
If cc= 1 then there is no interference and all double crossovers were observed..
