biology sample question

[RING12]

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In cucumber, Warty(W) is dominant over dull (w), and green(G) is dominant over orange(g). A cucumber plant that is homozygous for warty and green is crossed with one that is homozygous fordull and orange. The F1 generation is then crosses. If a total of 144 offspring are produced in the F2 generation, which of the following is the closest to the Number of dull green cucumbers expected?

a)3 b)10 c) 28 d)80 E)111

The answer is 28. But I dont understand it. can some one explain it to me plz?

 

[PhansterZ]

In cucumber, Warty(W) is dominant over dull (w), and green(G) is dominant over orange(g). A cucumber plant that is homozygous for warty and green is crossed with one that is homozygous fordull and orange. The F1 generation is then crosses. If a total of 144 offspring are produced in the F2 generation, which of the following is the closest to the Number of dull green cucumbers expected?

a)3 b)10 c) 28 d)80 E)111

The answer is 28. But I dont understand it. can some one explain it to me plz?

So the P1 general cross is WWGG X wwgg.
We get the F1 generation to be all WwGg.
Do a Punnett square and you see this is the case.

So F1 is all WwGg, so we cross them to get F2 generation.
WwGg X WwGg. Doing a punnett square, we get:

3 WWGG : Warty and Green
3 WwGG : Warty and Green
3 WwGg : Warty and Green
3 Wwgg : Warty and Orange
3 wwGg : dull and green
1 wwgg : dull and orange

So the ratio is:
9 Warty and Green
3 Warty and Yellow
3 Dull and Green
1 Dull and orange

Which means Dull and green has a ratio of 3/16 = 18.75%

144 X 18.75% = 27

Closest answer is 28.

You should memorize these ratios for dihybrid heterozygous cross (9:3:3:1).

 

[JamesBourne]

In cucumber, Warty(W) is dominant over dull (w), and green(G) is dominant over orange(g). A cucumber plant that is homozygous for warty and green is crossed with one that is homozygous fordull and orange. The F1 generation is then crosses. If a total of 144 offspring are produced in the F2 generation, which of the following is the closest to the Number of dull green cucumbers expected?

a)3 b)10 c) 28 d)80 E)111

The answer is 28. But I dont understand it. can some one explain it to me plz?

You should first realize this is a dihybrid cross (between F1 generations) and dihybrid crosses result in 9:3:3:1 ratio of phenotypes. 9 = dominant phenotype 3 = one dominant, one recessive 3 = diff. order but still one dominant and one recessive 1= recessive phenotype. Knowing dull green is a mix of dominant and recessive phenotypes, 3/16 * 144 gives 27, I guess they want you to choose the closest answer here.

 

[herkulease]

this is a dihybrid cross.

you get about 9:3:3:1 phenotypic ratio in theory.

9/16 will display both dominate traits

3/16 will display display dominate trait for 1st, recessive trait for the 2nd.

another 3/16 will display recessive of 1st trait, dominant of the 2nd

1/16 will display both recessive traits.

So here we want the number of cumbers that are Green and dull.

3/16 * 144 = would give us 27.

the only choice that is close to 27 is choice C, which is 28.

 

[RING12]

thanks every one!!!