28. A geneticist in conducting an experiment by making a testcross. She expects
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28. A geneticist in conducting an experiment by making a testcross. She expects the offspring of the test could be Cross to result in a 1:2:1 ratio. She wants to see if her data for the three phenotypic classes reasonably assumed to have deviated from the expected values by chance. How many degrees of freedom should she use when evaluating the chi-square goodness-of-fit test ? B) 2 C) 3 D) 4 E)5 29) 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 difference between observed and expected could be a result of chance. 30) Albinism is a recessive condition resulting from the inability to produce the dark pigment melanin in skin and hair. A man and woman with normal skin pigmentation want to have two children. The man s one parent with albinism; the woman has parents with normal pigmentation but a brother with albinism. a. What is the probability that at least one child will have albinism ? b. What is the probability of both children having normal pigmentation?Explanation / Answer
28) answer-B) The number of classes of offspring obtained in a 1:2:1 ratio are 3(n). The degree of freedom is given by the formula which is equal to n-1=3-1=2. It is an example of monohybrid cross in which four progeny are formed in the ratio of 1:2:1.
29)Two pea plants with purple flowers are crossed and the progeny obtained are as follows namely 63 purple flowers and 17 white flowers.
Observed purple flowers= 63, Expected purple flowers=60.
Observed white flowers=20, expected white flowers=17.
Chi-square test for purple flowers is = (O-E)2/ E= (63-60)2/60= 9/60=0.15.
Chi-square test for white flowers is=(O-E)2/ E= (20-17)2/20=9/20=0.45
Degree of freedom =2-1=2.
Total chi-square value is equal to =0.45+0.15=0.60.
The hypothesis at 5% level of significance cannot be rejected and is thus a result of chance.
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