Question

In cucumbers, green color (W) is dominant over yellow color (w) and spiked cucumbers (D) are dominant over smooth cucumbers (d). A cucumber plant true-breeding for green, spiked cucumbers is crossed with a plant true-breeding for yellow, smooth cucumbers.

1. What will the phenotypes and genotypes of the F1 generation be?

2. If the above F1 progeny are self-crossed, what ratio of the F2 offspring will be:

WwDd

wwDd

WWDD

wwDD

3. What ratio will have green spiked cucumbers?

4. What ration will have green, smooth cucumbers?

5. If the F1 progeny were used in test cross what ratio of the offspring would be:

green smooth cucumbers

Green smooth cucumbers

Answer 1

Sol.

(1)

Given,in cucumbers green color (W) is dominant over yellow colour (w) and spiked cucumbers (D) are dominant over smooth cucumbers (d).

Genotype of plants true breeding for green, spiked cucumbers is WWDD.

Genotype of plants true breeding for yellow, smooth cucumbers is wwdd.

F1 generation can be easily determined with the help of Punnette square for the cross between true breeding green, spiked cucumbers and true breeding yellow, smooth cucumbers as follows

Genotype of gametes produced by them will be WD and wd.

♂➡ ♀⬇	WD	WD
wd	WwDd	WwDd
wd	WwDd	WwDd

Here,all the offsprings from the above cross are having genotype WwDd. So, the F1 progenies from the above cross will be green, spiked cucumbers.

(2)

F2 generation can be easily determined with the help of Punnette square by self crossing the F1 progenies as follows

Genotype of gametes produced by them will be WD,Wd,wD and wd.

♂➡ ♀⬇	WD	Wd	wD	wd
WD	WWDD	WWDd	WwDD	WwDd
Wd	WWDd	WWdd	WwDd	Wwdd
wD	WwDD	WwDd	wwDD	wwDd
wd	WwDd	Wwdd	wwDd	wwdd

Ratio of the F2 offspring will be:

WwDd : 4/16

wwDd : 2/16

WWDD : 1/16

wwDD : 1/16

(3)

The ratio of offsprings having green spiked cucumbers will be 9/16

(4)

The ratio of offsprings having green smooth cucumbers will be 3/16

(5)

In a typical test cross an organism showing a dominant phenotype is crossed with the recessive parent instead of self crossing.

Here, when F1 progeny i.e. green spiked cucumbers having genotype WwDd is crossed with the recessive parent i.e. yellow smooth cucumbers having genotype wwdd, the progenies can be easily determined with the help of Punnette square as follows

Gametes produced by F1 progeny will be WD,Wd,wD and wd and the recessive parent will produce gametes having genotype wd.

♂➡ ♀⬇	WD	Wd	wD	wd
wd	WwDd	Wwdd	wwDd	wwdd

The ratio of offsprings having green smooth cucumbers will be 1/4 i.e. 25% .