Recombination Frequencyand

Gene Linkage Mapping

Linked vs. Unlinked Genes

Crossing Over

Crossover Frequency

Mapping Using Frequency

Mapping Gene Loci

Recombination frequency

(Recombinant offspring)

(Total offspring)

• A wild-type fruit fly (heterozygous for gray body color and normal wings) was mated with a black fly with vestigial wings. The offspring has the following phenotypic distribution:

• Wild type 778• Black-vestigial 785• Black normal 158• Gray vestigial 162

• What is the recombination frequency between these genes for body color and wing type?

• A wild-type fruit fly (heterozygous for gray body color and normal wings) was mated with a black fly with vestigial wings. The offspring has the following phenotypic distribution:

• Wild type 778• Black-vestigial 785• Black normal 158• Gray vestigial 162

• What is the recombination frequency between these genes for body color and wing type?

(158+162) / (778+785+158+162)

320/1873

0.171 = 17.1%

• In rabbits the dominant allele B produces a black coat color and the recessive genotype bb produces a brown coat.

• Body fat color in rabbits is white if a dominant allele Y is present and yellow if the genotype is yy.

• Assume the mating between rabbits with the following genotypes :Black with white fat – BBYYBrown with yellow fat - bbyy

• produces the dihybrid - BbYy Black with white fat• Calculate the recombination frequency if the dihybrids

are mated back to brown rabbits having yellow fat, bbyy, and the following ratio of phenotypes is observed:– BlackWhite125– BlackYellow75– BrownWhite85– BrownYellow115

• In rabbits the dominant allele B produces a black coat color and the recessive genotype bb produces a brown coat.

• Body fat color in rabbits is white if a dominant allele Y is present and yellow if the genotype is yy.

• Assume the mating between rabbits with the following genotypes :Black with white fat - BBYYBrown with yellow fat - bbyy

• produces the dihybrid - BbYy • Calculate the recombination frequency if the dihybrids

are mated back to brown rabbits having yellow fat, bbyy, and the following ratio of phenotypes is observed:– BlackWhite125– BlackYellow75– BrownWhite85– BrownYellow115

(75+85) / (125+115+75+85)

160/400

0.40 = 40%

Question #1• In rabbits, black (B) is dominant to brown (b), while

full color (F) is dominant to chinchilla (f). The genes controlling these traits are linked.

• The following cross was made: rabbits heterozygous for both traits that express black, full color, (BbFf) with rabbits that are brown, chinchilla (bbff). The following results were obtained:

o31 brown, chinchilla (bbff)o35 black, full (B-F-)o16 brown, fullo19 black, chinchilla

• Determine the map distance between the 2 genes.

Question #1• In rabbits, black (B) is dominant to brown (b), while

full color (F) is dominant to chinchilla (f). The genes controlling these traits are linked.

• The following cross was made: rabbits heterozygous for both traits that express black, full color, with rabbits that are brown, chinchilla. The following results were obtained:

o31 brown, chinchillao35 black, fullo16 brown, full o19 black, chinchilla

• map distance between the 2 genes

(16+19) / (31+35+16+19)

35/101

0.35 = 35%

35 map units

• Determine the sequence of genes along a chromosome based on the following recombination frequencies:

• b – vg 17

• cn-vg 8

• b-cn 9

• Determine the sequence of genes along a chromosome based on the following recombination frequencies:

• b – vg 17

• cn-vg 8

• b-cn 9

• Determine the sequence of genes along a chromosome based on the following recombination frequencies:

• b – vg 17

• cn-vg 8

• b-cn 9

• Determine the sequence of genes along a chromosome based on the following recombination frequencies:

• A-B 8

• A-C 28

• A-D 25

• B-C 20

• B-D 33

• Determine the sequence of genes along a chromosome based on the following recombination frequencies:

• A-B 8

• A-C 28

• A-D 25

• B-C 20

• B-D 33