Question

A female Drosophila fly is heterozygous for three recessive pigmentation mutations called pk, bk, and tp. pk is associated with pink eyes, bk is associated with black body, and tp is associated with transparent wings. A geneticist crosses this fly to a male pink, black, transparent fly and obtains 1000 progeny distributed as follows.

Phonotype Number Phenotype Number
Black 47 transparent 203
Wild type 204 black, transparent 49
Pink, transparent 46 pink, black, transparent 202
Pink, black 201 pink 48
Based on the data in this table, which genes are linked?
- bk and tp
- pk and tp
- pk and bk
Calculate the distance between the linked genes
___ m.u

Answer 1

The genes bk and tp are linked, while pk is independently assorting. The distance between the linked genes bk and tp is 9.5 m.u (map units).

Step-by-step explanation:

The data provided in the table shows the phenotypic distribution of the progeny resulting from a cross between a female fly heterozygous for three recessive pigmentation mutations (pk, bk, tp) and a male fly with pink eyes, a black body, and transparent wings.

Based on the data, we can determine the linkage between the genes pk, bk, and tp. The progeny distribution reveals that the phenotypes of black and transparent (49) and pink, black, and transparent (46) are relatively close in number, while the phenotypes of pink and transparent (202) and pink and black (201) are also relatively close in number. This suggests that the genes bk and tp are linked, while pk is independently assorting.

To calculate the distance between the linked genes, we can use the formula:

Distance = (Number of recombinants / Total number of offspring) x 100

In this case, the recombinant phenotypes are pink, black, and transparent (46) and black and transparent (49), so the distance between the linked genes bk and tp is (46 + 49) / 1000 x 100 = 9.5 m.u (map units).

Answer 2

The linked genes are pk and bk based on the progeny data, as these phenotypes appear most frequently, indicating that they are inherited together. Calculating the distance involves summing the recombinant progeny's numbers, dividing by the total number of offspring, and multiplying by 100 to get the genetic distance in map units, which is 9.7 m.u.

Step-by-step explanation:

The student wants to determine which of the three genes (pk, bk, and tp) in Drosophila are linked and to calculate the genetic distance between them. In Drosophila genetics, linked genes do not assort independently but are inherited together because they are located on the same chromosome. The offspring phenotypes that occur in the highest numbers are usually indicative of the parent's genotype whereas the least common phenotypes suggest recombination between the linked genes.

After examining the provided progeny data, we observe that the phenotypes 'pink, black' and 'transparent' appear most frequently, suggesting that the alleles for these traits (pk and bk) are linked. These alleles are inherited together from the heterozygous female parent. Conversely, the 'black, transparent' and 'pink' phenotypes occur in significantly lower numbers, which indicates recombination events.

To calculate the distance between the linked genes pk and bk, we add the number of recombinant progeny (pink and black, transparent phenotypes) and divide it by the total number of offspring, then multiply by 100 to convert to map units (m.u). The formula looks like this:

1. 
   
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Therefore, the genetic distance between the pk and bk genes is 9.7 map units.