Both of the genes involved in the dihybrid cross described above have been ident

Question

Both of the genes involved in the dihybrid cross described above have been identified molecula with DNA distinctions between their respective alleles. rly This gel diagram shows the DNA banding patterns observed among the F2 progeny of the Mendelian F1 x F1 cross. The parental samples are shown on the left (P1 and P2). On the right are shown all of the different patterns of bands observed among the F2 progeny. (Remember: The two pairs of alleles assort independenty.) P1nP2 A n B D n E Note: These gels indicate only the sizes of the DNA fragments represented. There's no information about the relative amounts: The thickness of all bands has been drawn the same for simplifying the analysis. What fraction of the F2 progeny would be expected to show pattern D? Enter your answer as a fraction

Explanation / Answer

From the parent lane it is understood that they are heterozygous in nature since all the lane has the bands.

Lets number each row as 1,2,3,4 in the gel.

Step 1. First we need to find the alleles of a gene. Since parents are heterozygous it is understood that there are 2 genes only.

Lane C shows that 1 and 2 are not alleles. (absence of band)

Lane G shows that 3 and 4 are not alleles.

Hence it can be implied that

A. 1 and 3 are alleles

B. 2 and 4 are alleles

Step 2. Lane D observations

2 bands are observed in 1 and 3 which shows heterzygocity.

1 band is observed in 2 and 4 which shows homozygocity.

Probability of heterozygocity = 2/4 = 1/2

Probability of homozygocity = 1/4

Overall fraction = (1/2) * (1/4) = 1/8

3. Step 3 Lane I observation

Only one band in 1 and 3 - homozygous

Only one band in 2 and 4 - homozygous

Fraction = (1/4) * (1/4) = 1/16

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