In an East Indian mango, three genes are linked on the same chromosome. Heavy bloom is dominant to light bloom, skin that is green is dominant to skin that is yellow, and fruit with a long shape is dominant to ovate shape. A plant that is true-breeding for the dominant traits was crossed to a light, yellow and ovate fruit. The F1 plants were then testcrossed to light, yellow and ovate fruit. The following results were obtained:
251 heavy, green, long
111 heavy, green, ovate
133 heavy, yellow, ovate
21 heavy, yellow, long
255 light, yellow, oblate
129 light, yellow, long
112 light, green, long
1 light, green, ovate
a) Diagram the crosses for the parental generation and F1 test cross.
Construct a genetic map that shows the order of these three genes and the distances between them.
a) Parental generation:
Heavy, green, long (Hh Gg Ll) x Light, yellow, ovate (hh gg ll)
F1 Test cross:
F1 (Hh Gg Ll) x Light, yellow, ovate (hh gg ll)
b) To construct a genetic map, we first need to determine the recombination frequencies between the traits.
251 + 129 + 1 + 112 = 493 (total offspring in the F2)
(251+129)/493 = 0.742 (recombination frequency between heavy bloom and oblate fruit)
(129+1)/493 = 0.264 (recombination frequency between oblate fruit and green skin)
(1+112)/493 = 0.236 (recombination frequency between green skin and heavy bloom)
Based on these recombination frequencies, we can order the genes as follows:
Heavy bloom - oblate fruit - green skin - long fruit
The distances between the genes can be calculated by multiplying the recombination frequencies by 100:
Heavy bloom and oblate fruit: (0.742) x 100 = 74.2 map units
Oblate fruit and green skin: (0.264) x 100 = 26.4 map units
Green skin and long fruit: (0.236) x 100 = 23.6 map units
Therefore, the genetic map for these three linked genes is:
Heavy bloom --- 74.2 map units --- oblate fruit --- 26.4 map units --- green skin --- 23.6 map units --- long fruit
Oh boy, it's time to get mapping! Let's get started on this genetic adventure:
Parental generation cross:
- Heavy, green, long x Light, yellow, ovate
F1 test cross:
- F1 plants (unknown genotype) x Light, yellow, ovate
Now, let's dive into constructing the genetic map:
Step 1: Determine the gene order
To determine the gene order, we need to analyze the results of the F1 test cross. Let's see which traits showed up most frequently:
- Heavy, green, long: 251
- Heavy, yellow, ovate: 133
- Heavy, green, ovate: 111
- Heavy, yellow, long: 21
- Light, yellow, oblate: 255
- Light, yellow, long: 129
- Light, green, long: 112
- Light, green, ovate: 1
From these results, we can see that the most common combination is heavy (dominant), green (dominant), and long (dominant). So, let's put these first in our gene order:
- Gene 1: Heavy (H)
- Gene 2: Green (G)
- Gene 3: Long (L)
Step 2: Determine the distances between genes
Now, we need to figure out the distances between these genes. To do this, we'll look at the results that differ from the most common combination. Let's analyze the numbers:
- Heavy, green, ovate: 111
- Heavy, yellow, ovate: 133
- Heavy, yellow, long: 21
- Light, yellow, oblate: 255
- Light, yellow, long: 129
- Light, green, long: 112
- Light, green, ovate: 1
From these results, we can see that heavy, green and ovate are more common than the other variations. So, let's assume these are the closest together:
- Gene 1 (H) ------ Gene 2 (G) ------------------ Gene 3 (L)
Now, let's place the other genes based on their numbers:
- Gene 1 (H) ------ Gene 2 (G) ------ Gene 3 (L)
- Heavy, yellow, long: 21 (between H and G)
- Light, green, long: 112 (between G and L)
- Light, green, ovate: 1 (closest to L)
Gene 1 (H) ------ Gene 2 (G) ------ Gene 3 (L)
- Heavy, yellow, long: 21
- Light, green, long: 112
- Light, green, ovate: 1
And there you have it, our genetic map! It shows the gene order and the distances between them:
Gene 1 (H) ------ Gene 2 (G) ------ Gene 3 (L)
- Heavy, yellow, long: 21
- Light, green, long: 112
- Light, green, ovate: 1
Hope this genetic mapping journey brought a smile to your face!
To diagram the crosses for the parental generation and F1 test cross, we need to use the symbols for the different traits. Let's use "H" for heavy bloom, "L" for light bloom, "G" for green skin, "Y" for yellow skin, "Lg" for long shape, and "O" for ovate shape.
Parental generation cross:
Heavy green long (true-breeding) x Light yellow ovate
F1 generation test cross:
F1 (heavy green long OR HGL) x Light yellow ovate (LYO)
Now, let's construct a genetic map to show the order of the three genes and the distances between them:
1. Determine the gene order:
Based on the results, we can see that heavy bloom (H) is always followed by green skin (G), and green skin (G) is always followed by long shape (Lg). Therefore, the gene order is:
H - G - Lg
2. Calculate the distances between the genes:
To calculate the distances between the genes, we need to examine the different combinations in the F1 test cross.
From the F1 test cross results:
251 HGL
111 HGO
133 HYO
21 HYL
255 LYO
129 LYL
112 LGL
1 LGO
Let's look at the cases that involve a change in a single gene at a time:
- From HGL to HGO: 111 individuals (HGO) / 364 total individuals = 30.49%
- From HGO to HYO: 133 individuals (HYO) / 364 total individuals = 36.54%
- From HYO to HYL: 21 individuals (HYL) / 364 total individuals = 5.77%
- From HYL to LYO: 255 individuals (LYO) / 364 total individuals = 70.05%
- From LYO to LYL: 129 individuals (LYL) / 364 total individuals = 35.44%
- From LYL to LGL: 112 individuals (LGL) / 364 total individuals = 30.77%
- From LGL to LGO: 1 individual (LGO) / 364 total individuals = 0.27%
Now, let's create the genetic map with the distances between the genes:
H - 30.49 cM - G - 6.77 cM - Lg
Note: The cM (centiMorgan) is the unit used to measure the distances between genes on a genetic map.
So, the genetic map for these three genes in an East Indian mango is:
H - 30.49 cM - G - 6.77 cM - Lg
To diagram the crosses for the parental generation and F1 test cross, you need to represent the alleles of each gene for both parents and the resulting offspring.
Let's represent the dominant alleles with uppercase letters and the recessive alleles with lowercase letters:
Parental generation:
Heavy bloom (H) x Light bloom (h)
Green skin (G) x Yellow skin (g)
Long shape (L) x Ovate shape (l)
F1 generation (parental traits are dominant):
HhGGll x hhggll
To construct a genetic map that shows the order of the genes and the distances between them, we need to analyze the resulting offspring from the F1 test cross.
Let's calculate the frequencies of each combination of traits:
251 heavy, green, long (HGL)
111 heavy, green, ovate (HGo)
133 heavy, yellow, ovate (Hyo)
21 heavy, yellow, long (HyL)
255 light, yellow, oblate (hyO)
129 light, yellow, long (hyL)
112 light, green, long (hGL)
1 light, green, ovate (hGo)
Now, let's determine the gene order and distances between them:
1. We can see that the trait heavy bloom (H) is always inherited together with the trait green skin (G), indicating they are linked.
2. The trait green skin (G) and the trait long shape (L) do not recombine because all offspring with green skin (G) also have the long shape (L) trait. Therefore, they are also linked.
3. The trait long shape (L) and the trait yellow skin (g) can recombine:
- The combination HGL (251) represents the highest frequency offspring.
- The combination HGo (111) represents the second-highest frequency offspring.
- The combination Hyo (133) represents the third-highest frequency offspring.
- The combination HyL (21) represents the fourth-highest frequency offspring.
Based on these frequencies, we can conclude that the gene order is H-G-L.
To calculate the distances between the genes, we need to compare the frequencies of recombinant offspring with the total number of offspring:
Recombination frequency between genes H and G:
(111+133) / (251+111+133+21) = 244 / 516 = 0.473
This indicates a recombination frequency of 47.3% between genes H and G.
Recombination frequency between genes G and L:
21 / (21+251) = 21 / 272 = 0.077
This indicates a recombination frequency of 7.7% between genes G and L.
Therefore, the genetic map for the three genes is as follows:
H (47.3 cM) - G (7.7 cM) - L
Note: The distances between the genes are given in centimorgans (cM).