Calculate the map distance, draw a map showing the locations of the genes and the distances between them, Calculate recombination interference.

Question

SHOW WORK. A triple heterozygote shows the wild-type phenotype for three genes a, b, and c. You test cross that triple heterozygote, and observe the progeny classes below.

A. Calculate the map distance in cM between the central gene and each flanking gene, then draw a map showing the locations of the genes and the distances between them.

B. Calculate recombination interference.

SHOW ALL WORK.

 

Phenotype                      number observed

abc                                  3

+++                                   2

++c                                 69

+b+                                 23

a++                                 416

ab+                                 60

+bc                                 402

a+c                                 25

                            total:1000

Answer 1

To calculate the map distance between the central gene and each flanking gene, we first need to determine the recombination frequencies for each gene combination. We will use the observed progeny classes to do this.

Given:

Total progeny observed (n) = 1000

Observed progeny classes:

- abc: 3

- +++: 2

- ++c: 69

- +b+: 23

- a++: 416

- ab+: 60

- +bc: 402

- a+c: 25

We can use the formula for recombination frequency (RF):

RF = (Recombinant progeny / Total progeny) * 100

A. Calculate the recombination frequencies for each gene combination:

1. RF(ab+): (60 / 1000) * 100 = 6%

2. RF(a+c): (25 / 1000) * 100 = 2.5%

3. RF(++c): (69 / 1000) * 100 = 6.9%

4. RF(+bc): (402 / 1000) * 100 = 40.2%

5. RF(+b+): (23 / 1000) * 100 = 2.3%

Now, we'll calculate the map distance between the central gene (c) and each flanking gene (a and b):

1. Map distance between c and a:

RF(a+c) + RF(ab+) = 2.5% + 6% = 8.5 cM

2. Map distance between c and b:

RF(++c) + RF(+bc) = 6.9% + 40.2% = 47.1 cM

B. To calculate recombination interference, we'll use the formula:

Interference (I) = 1 - (Double recombinants / (Single recombinants1 * Single recombinants2))

Here, we'll calculate interference between genes a and b:

1. Single recombinants between a and c (Sra+c) = RF(a+c) = 2.5%

2. Single recombinants between c and b (Src+b) = RF(+bc) = 40.2%

3. Double recombinants (Dr) = RF(ab+) = 6%

Interference (I) = 1 - (6% / (2.5% * 40.2%))

= 1 - (6% / 1.005%)

= 1 - 5.9701493

= -4.9701493

The negative value of interference indicates interference. However, it's unusual to have negative interference. This may indicate that the data is not fitting the expected pattern, or there may be other factors affecting the outcome.