Two pea plants with purple flowers are crossed. Among the offspring, 63 have purple flowers, and 17 have white flowers. With a chi-square test, compare the observed numbers with a 3:1 ratio and determine if the the difference between observed and expected is statistically significant. Note: Chi-square critical value with 1 degree of freedom is 3.84 with alpha equal to 0.05

Chi-square value = 0.6

The difference between the observed individuals and the expected individuals is not statistically significant. There is not enough evidence to reject the null hypothesis.

Explanation:

 H₀= Individuals will be equally distributed  

H₁ = Individuals will not be equally distributed.  

•Chi square= ∑ ((O-E)²/E)  

∑ is the sum of the terms

O are the Observed individuals  

E are the Expected individuals  

•Freedom degrees = 1  

•Significance level, 5% = 0.05  

•Table value/Critical value = 3.84  

The number of observed individuals:

Total number of individuals, N = 80 = 63 + 17

Observed Genotypic frequencies:

p² + 2pq + q² = 1

p² + 2pq = F(PF)

0.79 + 0.21 = 1

The expected genotypic frequency:

F (PF)= 0.75  

F (pf) = 0.25

 The number of expected individuals:

Chi square = sum (O-E)²/E

PF =(63 - 60) ² / 60

PF = 0.15

pf= (17 - 20)²/20

pf= 0.45

  Chi square= sum ((O-E)²/E) = 0.15 + 0.45 = 0.60

0.6 < 3.84 meaning that the difference between the observed individuals and the expected individuals is not statistically significant. There is not enough evidence to reject the null hypothesis. Probably both parentals were heterozygous for the trait.  

parasites can detrimentally affect their host, but also must not allow their host to die before they can complete their life cycle. some parasites have complex life cycles with many different hosts, and have had to find ways of persisting in many different environments during the change from one host to another. ectoparasites live outside the body of the host, and can more easily  disperse, but are  more exposed to predators, parasites, parasitoids. endoparasites live inside the body of the host, and are therefore protected from the outside environment. but they can be  attacked by the host's immune system. they have therefore developed  mechanisms for dispersal such as  complex life cycles.