In crickets, long wings are dominant over short wings and green abdomens are dom

ID: 88926 • Letter: I

Question

In crickets, long wings are dominant over short wings and green abdomens are dominant over yellow abdomens. A cricket homozygous for both long wings and green abdomen is crossed with a cricket that has short wings and a yellow abdomen. The F1 progeny are then subjected to a test cross with a cricket with both recessive traits and the following progeny are obtained:

130 long wings, green abdomen 152 long wings, yellow abdomen 107 short wings, green abdomen 111 short wings, yellow abdomen .

Assuming that these alleles are not linked, what is the closest X2 value for this cross?

Explanation / Answer

Let long wings be L and short wings be l.

Let green abdomen be G and yellow abdomen be g.

The test cross is between

LlGg X llgg

LlGg parent produces four types of gametes (LG, Lg, lG and lg)

llgg parent produces one type of gamete (lg)

The offsprings will be LlGg, Llgg, llGg and llgg in 1:1:1:1 ratio.

There are a total of 500 offsprings. So all the all the four types of offsprings should be 125 each in number.

Phenotype

O-E

(O-E)2

(O-E)2/E

LlGg

130

125

0.2

Llgg

152

125

729

5.832

llGg

107

125

-18

324

2.592

llgg

111

125

-14

196

1.568

Total

500

10.192

2 = 10.192

so 2 value for this cross is 10.192