Crossing Over Frequencies and Gene Mapping

Question 1

Linked genes

Answer 1

genes that exist on the same chromosome (e.g., if the acne gene and belly fat gene are on the same chromosome, then they are linked; with A and B linked together and a and b linked together, or vice versa)

Question 2

Parental type

Answer 2

in a linkage cross, if the offspring look like either parent, then they are parental types (e.g., if we assume A and B are linked together and a and b are linked together in the linkage cross AaBb X aabb, any offspring that are AaBb or aabb are parental types)

Question 3

Non-parental type

Answer 3

in a linkage cross, any offspring of the above cross that don’t look like the parents (Aabb or aaBb) are non-parental types, are the results of crossing over, and are recombinants

Question 4

Recombinations frequency

Answer 4

the number of recombinant offspring divided by the total number of offspring X 100; expressed as a percentage; used as a map distance between the two genes (e.g., the recombination frequency was 32%, therefore the two genes are 32 map units apart on the chromosome)

Question 5

Map distance

Answer 5

how far apart (in centimorgans) two genes are on a chromosome; the recombination frequency from a linkage cross is used as the map distance between two genes (e.g., 44% of the offspring of the linkage cross were recombinants, therefore the two genes are 44 map units or 44 cM apart)

Question 6

Recombination

Answer 6

during crossing over in prophase I of meiosis, genes from non-sister chromatids trade places, making new allele combinations in the gametes (e.g., if A is linked to B and a to b, then any gametes that are Abor aB are the results of recombination or crossingover)

Question 7

Map unit

Answer 7

the unit used is the centimorgan (cM); because the recombination frequency is a percentage, the largest map distance is 100 cM

Question 8

Crossover percentage

Answer 8

same as recombination frequency