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4. In a population of 50 randomly-mating laboratory mice contains 30 black (dominant- BB& Bb) colour and 20 are white colour (Recessive -bb). Calculate allelic and genotypic frequencies for this population and validate your results statistically using chi-square.


Sagot :

Okay, let's work through this step-by-step:

Given information:

Total population size: 50 mice

30 black (dominant) mice

20 white (recessive) mice

Step 1: Calculate the allelic frequencies.

The alleles for coat color in this case are B (black) and b (white).

Frequency of B allele = (2 × Number of BB) + (Number of Bb) / (2 × Total population size)

Frequency of B allele = (2 × 15) + 15 / (2 × 50) = 0.6

Frequency of b allele = (2 × Number of bb) + (Number of Bb) / (2 × Total population size)

Frequency of b allele = (2 × 20) + 15 / (2 × 50) = 0.4

Step 2: Calculate the genotypic frequencies.

BB = 15 / 50 = 0.3

Bb = 15 / 50 = 0.3

bb = 20 / 50 = 0.4

Step 3: Validate the results using the chi-square test.

Null hypothesis (H0): The observed genotypic frequencies are consistent with the Hardy-Weinberg equilibrium.

Alternative hypothesis (H1): The observed genotypic frequencies are not consistent with the Hardy-Weinberg equilibrium.

Expected frequencies:

p^2 (BB) = (0.6)^2 = 0.36

2pq (Bb) = 2 × 0.6 × 0.4 = 0.48

q^2 (bb) = (0.4)^2 = 0.16

Chi-square statistic:

χ^2 = Σ [(Observed - Expected)^2 / Expected]

χ^2 = [(15 - 18)^2 / 18] + [(15 - 24)^2 / 24] + [(20 - 8)^2 / 8]

χ^2 = 0.5 + 4.5 + 9

χ^2 = 14

Degrees of freedom = 3 - 1 = 2

At a significance level of 0.05, the critical value of χ^2 with 2 degrees of freedom is 5.991.

Since the calculated χ^2 value (14) is greater than the critical value (5.991), we reject the null hypothesis. The observed genotypic frequencies are not consistent with the Hardy-Weinberg equilibrium.

In summary:

Allelic frequencies:

B = 0.6

b = 0.4

Genotypic frequencies:

BB = 0.3

Bb = 0.3

bb = 0.4

The chi-square test indicates that the observed genotypic frequencies are not consistent with the Hardy-Weinberg equilibrium.