In Drosophila melanogaster, cut wings (ct) is recessive to normal wings (ct+), sable body (s) is recessive to gray body (s+), and vermilion eyes (v) is recessive to red eyes (v+). All three recessive mutations are X- linked. A female fly with cut wings, sable body, and vermilion eyes is crossed to a male with normal wings, gray body, and red eyes. The F1 females produced by this cross were mated with cut, sable, vermilion males in a testcross. The following are the progeny resulting from the testcross.
v ct s 510
v+cts 1
v+ ct+ s 14
v+ ct+ s+ 500
v+cts+ 73
v ct s+ 20
v ct+ s 81
v ct+ s+ 1
Total 1200
Determine the order of these genes on the chromosome.
Calculate the map distances between the genes.
Determine the coefficient of coincidence and the interference among these genes.
Well, it looks like we've got quite the genetic puzzle on our hands! Let's see if we can unravel it.
To determine the order of the genes on the chromosome, we can examine the progeny resulting from the testcross. From the data provided, we can observe that there are two double-crossover events, which will help us figure out the gene order.
First, let's identify the double-crossover progeny. These are the ones that have the least number of offspring. In this case, we have the following double-crossover progeny: v+cts and v ct+ s+. So, we know that these two genes are the ones that experienced the double-crossover.
Now, let's look at the single-crossover progeny. These are the progeny that have the highest number of offspring. From the data provided, we can see that there are four single-crossover progeny: v ct s, v+ ct s, v+ ct+ s, and v ct s+.
Based on this information, we can deduce the gene order is v - ct - s.
Now, let's move on to calculating the map distances between the genes. To do this, we need to determine the recombination frequencies between each pair of genes.
The recombination frequency between v and ct genes can be calculated by adding the number of offspring with v ct and v+ ct+ alleles and dividing it by the total number of offspring. From the data provided, we have 510 v ct offspring and 14 v+ ct+ offspring, resulting in a recombination frequency of (510 + 14) / 1200 = 0.4375.
Similarly, the recombination frequency between ct and s can be calculated by adding the number of offspring with v+ ct+ s+ and v ct s alleles and dividing it by the total number of offspring. We have 500 v+ ct+ s+ offspring and 20 v ct s offspring, resulting in a recombination frequency of (500 + 20) / 1200 = 0.4333.
Lastly, the recombination frequency between v and s genes can be calculated by adding the number of offspring with v+ ct+ s and v ct s+ alleles and dividing it by the total number of offspring. We have 1 v+ ct+ s offspring and 81 v ct s+ offspring, resulting in a recombination frequency of (1 + 81) / 1200 = 0.0675.
Now that we have the recombination frequencies, we can convert them to map units. Since there are 100 map units between genes, we can multiply the recombination frequencies by 100 to get the map distances.
The map distance between v and ct genes is 0.4375 * 100 = 43.75 cM.
The map distance between ct and s genes is 0.4333 * 100 = 43.33 cM.
The map distance between v and s genes is 0.0675 * 100 = 6.75 cM.
Now, let's move on to determining the coefficient of coincidence and the interference.
The coefficient of coincidence (C.O.C.) is the ratio of observed double-crossover events to the expected double-crossover events. In this case, we observed 2 double-crossover events, so the C.O.C. would be 2.
The interference is calculated by subtracting the C.O.C. from 1. In this case, the interference would be 1 - 2 = -1.
Since the value for interference is negative, it indicates that there is interference between the genes, meaning that the occurrence of one crossover event affects the occurrence of another.
And there you have it! We've determined the order of the genes on the chromosome, calculated the map distances between the genes, and determined the coefficient of coincidence and interference.
To determine the order of these genes on the chromosome, we can use the data from the testcross progeny. The progeny results indicate the different combinations of phenotypes observed, which can be used to infer the gene order.
First, we need to identify the gene that segregates independently of the other two genes. In this case, it is the vermilion eyes (v) gene because there are equal numbers of flies with vermilion eyes and sable body (vs.) as well as flies with vermilion eyes, normal wings, and sable body (v+ ct+ s vs.).
Next, we look at the combinations that involve the cut wings (ct) and sable body (s) genes. By comparing the numbers of flies with cut wings, sable body and vermilion eyes (ct s v) to the numbers of flies with cut wings, sable body, and red eyes (ct s v+), we can determine the gene order.
From the data, we can observe that there are 510 flies with the ct s v combination and only 1 fly with the ct s v+ combination. This indicates that the ct and s genes are usually inherited together, and the v gene is relatively farther away.
Therefore, the gene order can be inferred as ct - s - v.
Next, let's calculate the map distances between the genes. The map distance between two genes is the percentage of recombinant offspring observed.
To calculate the map distance between ct and s, we can add up the numbers of recombinant offspring (ct+ s and ct s+) and divide it by the total number of offspring. In this case, the numbers of recombinant offspring are 81 + 20 = 101, and the total number of offspring is 1200.
The map distance between ct and s can be calculated as follows:
Map distance (ct-s) = (Recombinant offspring / Total offspring) × 100
= (101 / 1200) × 100
≈ 8.42%
Similarly, to calculate the map distance between s and v, we add up the numbers of recombinant offspring (v+ s+ and v+ s) and divide it by the total number of offspring. In this case, the numbers of recombinant offspring are 73 + 14 = 87, and the total number of offspring is 1200.
The map distance between s and v can be calculated as follows:
Map distance (s-v) = (Recombinant offspring / Total offspring) × 100
= (87 / 1200) × 100
≈ 7.25%
Now, let's determine the coefficient of coincidence and the interference among these genes. The coefficient of coincidence (C.O.C) measures the degree of interference, which is the deviation from independent assortment.
The coefficient of coincidence can be calculated as follows:
C.O.C = (Observed double-crossover offspring) / (Expected double-crossover offspring)
From the data, we can see that there is only 1 fly with the v+ ct+ s+ combination, which represents the double-crossover offspring. The expected number of double-crossover offspring can be calculated by multiplying the individual recombinant frequencies (ct-s and s-v).
Expected double-crossover offspring = (Map distance ct-s) × (Map distance s-v) × Total offspring
= (8.42 / 100) x (7.25 / 100) × 1200
≈ 8.37
Therefore, the coefficient of coincidence can be calculated as follows:
C.O.C = Observed double-crossover offspring / Expected double-crossover offspring
= 1 / 8.37
≈ 0.119
Finally, to calculate the interference, we subtract the coefficient of coincidence from 1.
Interference = 1 - C.O.C
= 1 - 0.119
≈ 0.881
Therefore, the coefficient of coincidence is approximately 0.119, and the interference is approximately 0.881.