Question

# The F2 generation from a dihybrid cross produced a total of 219 tall plants with purple...

The F2 generation from a dihybrid cross produced a total of 219 tall plants with purple flowers, 72 dwarf plants with purple flowers, 69 tall plants with pink flowers, and 31 dwarf plants with pink flowers.

1: please state your hypothesis and explain how you arrived at this prediction

2:

 phenotype observe expected Purple, tall Purple, dwarf Pink, tall Pink, dwarf total number of plants in F2 generation

3: What is the chi-square value between the observed and expected offspring from the F2 generation for this dihybrid cross? (2 mark) Please report your chi-square value with 3 decimal places .

(a) What is the degrees of freedom for this dihybrid cross? Blank 1 (1 mark)

(b) What is the probability associated with your calculated chi-square value for this dihybrid cross?

Blank 2 < P < Blank 3

HINT: Make sure you enter the numbers on the correct side of the less than (>) symbols.

#### Homework Answers

Answer #1

1. Null hypothesis: The observed values are not deviating from the expected ratio i.e. 9:3:3:1.

2. Test staic:

 Category purple tall purple dwart pink tall pink dwarf Total Observed values 219 72 69 31 391 Exptected Ratio 9 3 3 1 16 Exprected Values 219.9375 73.3125 73.3125 24.4375 Deviation -0.9375 -1.3125 -4.3125 6.5625 D^2 0.878906 1.722656 18.59766 43.06641 D^2/E 0.003996 0.023497 0.253676 1.762308 2.043478 X^2 2.043478 Degrees of freedom 4 - 1 3

3: The chi-square value between the observed and expected offspring from the F2 generation = 2.043

(a) What is the degrees of freedom for this dihybrid cross? = 4-1 = 3

(b) What is the probability associated with your calculated chi-square value for this dihybrid cross? 7.82 at 3 DF and 0.05 probability.

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