Chapter 5C

Question 1

What do you need to do in a 3-point test cross?

Answer 1

• Determine the gene order
• Determine map distances between genes

Question 2

How do you determine gene order?

Answer 2

Compare the Double Recombinants to the Nonrecombinants (Double Recombinants are the lowest two progeny numbers and Nonrecombinants are the two highest progeny numbers).
Look at the genotype table, and look at one NR row and one DR row. From the two rows, look for two genotypes with matching symbols. The nonmatching one is the gene in the middle.

Question 3

How do you determine gene distances?

Answer 3

((double recombinants + single recombinants found using the chromosomal arrangement of alleles)/1000) and then that number times 100.
Example- the distance between y and sn is determined by classes divided by 1000 (same for the distance between v and sn) Then, the total distance between y and v is those two numbers added.

Question 4

What are three hints for calculating gene distance?

Answer 4

1. DR progeny numbers are used for both map distance calculations.
2. NR progeny numbers are never used in determining recombination distances
3. There are four SRs. If two numbers are used for one map distance calculation, the others will be used for the other map distance.

Question 5

What is the coefficient of coincidence equation?

Answer 5

(Number of observed double crossovers)/(Number of expected crossovers)
The number observed is the two DR progeny added together
- The number expected is both of the map units found (in decimal form) multiplied by 1000

Question 6

What is the Interference equation?

Answer 6

1 - Coefficient of coincidence

Question 7

What does interference show?

Answer 7

If there is a crossover at one spot on a chromosome, this decreases the likelihood of a crossover in a nearby spot on the same chromosome.

Question 8

What does the coefficient of coincidence show?

Answer 8

A measure of interference in the formation of chromosomal crossovers during meiosis