By the way, my homework is due Wednesday, November 13th at 4:10 pm. I would appreciate it if you could please walk me through all of the steps to solve all parts of this problem. If a triple-heterozygote is testcrossed and yields 3000 progeny, among them 259 are hairless tomato plants, 40 are hairless tomato plants with jointless fruit stems, 931 tomato plants have jointless fruit stems, 260 are normal tomato plants that produce the pigment anthocyanin, are hairy plants, and have jointed fruit stems, 268 of the progeny do not produce the pigment anthocyanin, have jointless fruit stems, and are hairless tomato plants, 941 do not produce the pigment anthocyanin and are hairless tomato plants, 32 do not produce the pigment anthocyanin, and 269 do not produce the pigment anthocyanin and have jointless fruit stems. Three genes on chromosome 5 of the tomato are: 'A'
(the recessive allele 'a' does not produce the pigment anthocyanin), 'H' (the recessive allele 'h' produces plants without hairs), and 'J' (the recessive allele 'j' produces jointless fruit stems).
a. What is the genotype of the triply-heterozygous parent?
b. What is the order of the three genes?
c. What is the recombination frequency between H & A?
d. What is the recombination frequency between H & J?
e. Draw a genetic map of these three genes.
f. What is the interference for these genes?
To solve this problem, we need to analyze the given information and apply the principles of genetics. Let's go through the steps together:
a. Determining the genotype of the triply-heterozygous parent:
From the information provided, we know that the recessive alleles for the three genes are 'a' (no pigment anthocyanin), 'h' (no hair), and 'j' (jointless fruit stems). Since the parent is triply-heterozygous, it means that it carries one dominant and one recessive allele at each gene locus. Therefore, the genotype of the triply-heterozygous parent can be represented as AaHhJj.
b. Determining the order of the three genes:
To determine the order of the three genes (A, H, J), we can observe the double-crossover progeny. From the information given, we can identify the following double-crossover progeny:
- 40 hairless tomato plants with jointless fruit stems (h-j)
- 260 normal tomato plants that produce the pigment anthocyanin, are hairy plants, and have jointed fruit stems (a-H-j)
From this, we can conclude that the order of the three genes is H-A-J.
c. Calculating the recombination frequency between H & A:
To calculate the recombination frequency between H & A, we need to determine the total number of progeny and the number of double-crossover progeny between these two genes. From the information given:
Total progeny (N) = 3000
Progeny with H & A double-crossover (h-a) = 259 + 268 = 527
Recombination frequency (RF) = (Number of double-crossover/h-a progeny / Total progeny) * 100
RF = (527/3000) * 100 = 17.57%
Therefore, the recombination frequency between H & A is 17.57%.
d. Calculating the recombination frequency between H & J:
To calculate the recombination frequency between H & J, we follow the same steps as before, using the information given:
Total progeny (N) = 3000
Progeny with H & J double-crossover (h-j) = 40
Recombination frequency (RF) = (Number of double-crossover/h-j progeny / Total progeny) * 100
RF = (40/3000) * 100 = 1.33%
Therefore, the recombination frequency between H & J is 1.33%.
e. Drawing a genetic map of these three genes:
Based on the information gathered so far, we can construct a genetic map with the following gene order and recombination frequencies:
H - 1.33 cM - A - 17.57 cM - J
f. Calculating the interference for these genes:
Interference is a measure of the reduction in the occurrence of double crossovers compared to what would be predicted based on the individual recombination frequencies. It is calculated using the following formula:
Interference = 1 - (Observed double crossovers / Expected double crossovers)
From the information given, the observed double crossovers for H & A (h-a) are 527, and the expected double crossovers (based on the individual recombination frequencies) can be calculated by multiplying the recombination frequencies of each gene pair:
Expected double crossovers = RF(H & A) * RF(H & J) * Total progeny
Expected double crossovers = 0.01757 * 0.0133 * 3000 = 7.02
Interference = 1 - (527/7.02) ≈ 99.25%
Therefore, the interference for these genes is approximately 99.25%.
By following these steps, you should be able to solve all parts of the problem.