Diploid Mapping 2point cross

1
Diploid Mapping (2-point cross)
a b X a a b b
wildtype albino/bent bent albino 110
125 370 395 1000 total
recombinants parentals
( recombinance) distance between a--b
110 125 / 1000 0.235 x 100 23.5 or 23.5
cM
2
Three - Point Cross

• determine gene order distance between 3 linked
  genes
• make a trihybrid and do a test cross

• determine parental types (2 most abundant)
  nonrecombinants
• 2) determine gene order look at double mutant
  recombinants
• (2 least abundant). The one allele type that
  is different from one
• of the parents would be the gene in the middle
• 3) diagram all of the offsprings genotypes
• 4) determine distance between a -- b
• single crossover single crossover double
  crossover double crossover
• total of
  offspring
• 5) determine distance between b -- c
• (use same formula but different single
  crossover values)

3
wt
abc X aabbcc

• albino, bent, crazy
• wildtype
• albino, bent
• crazy
• bent
• albino, crazy
• bent, crazy
• albino
• 1000 total

a - c 93 87 10 7 19.7 cM 1000
b - a 56 50 10 7 12.3 cM 1000
b - c 93875650107107 32.0 cM
1000
4
Double-Cross Over
the closer the genes, the lower the double
recombinance
observed double cross-over total of double
cross-overs total offspring
expected double cross-over (freq. b--a) X (freq.
a--c)
0.123 X 0.197 0.024
10 7 / 1000 0.017
5
Chromosome Interference
cross-overs in one region dec. the prob. of
second cross-over
Coefficient of coincidence observed double
recomb. expected double recomb.
one cross-over event reduces chance of second
cross-over event
Interference 1 - 0.017 0.29
0.024
6

• Find parental types, single and double
  recombinants,
• Determine the order of the genes and distance
• between them
• Determine if there is interference between the
  two
• cross-over events

abc X aabbcc

• 880 albino, crazy
• 887 bent
• 64 albino
• 67 bent, crazy
• 49 albino, bent
• 46 crazy
• 3 abino, bent, crazy
• 4 wildtype
• 2000 total