In a special breed of Halloween pumpkins, orange color (W) is dominant to white

ID: 66728 • Letter: I

Question

In a special breed of Halloween pumpkins, orange color (W) is dominant to white color (w) and speckled (G) is dominant to glittery (g). The genes controlling these traits are linked. Pumpkin plants that are heterozygous for both traits and express orange, speckled phenotypes were crossed with pumpkin plants that express white, glittery phenotypes, with the following results:

42 orange, speckled
38 white, glittery
7 orange, glittery
13 white, speckled

Determine the map distance between the two genes.

Using the map units that were obtained in question 1, answer the following question.
If crossing over occurs in both sexes, what proportion of offspring would be expected to have an orange, speckled phenotype if a cross is conducted between pumpkin plants with the following genotypes:

WG/wg x Wg/wG

Explanation / Answer

map distance = recombination frequency = number of recombinants

We have two recombinants, 7 orange, glittery;13 white, speckled

Recombination frequency = number of recombinants / total progeny

= 20 / 100

= 0.2

= 20 % = 20 mU

WwGg x WwgG

WWGG

WWGg

WwGG

WwGg

WWgG

WWgg

WwgG

Wwgg

wWGG

wWGg

wwGG

wwGg

wWGgG

wWgg

wwgG

wwgg

From above cross cross orange, speckled phenotype = 9 / 16 = 56.0 %

So, out of total 100 progeny 56 will be of orange, speckled phenotype