I think that I understand,but still seem stuck on these questions from my exam.
ID: 10421 • Letter: I
Question
I think that I understand,but still seem stuck on these questions from my exam.1. In the garden pea, orange pods (orp) are recessive to green pods (orp +), and sensitivity to pea mosaic virus (mo) is recessive to resistance to the virus (mo +). A plant with orange pods and sensitivity to the virus was crossed to a true breeding plant with green pods and resistance to the virus. The F1 plants were then test crossed to plants with orange pods and sensitivity to the virus. The following results were obtained:
160 orange pods, virus sensitive
165 green pods, virus resistant
36 orange pods, virus resistant
39 green pods, virus sensitive
___
400 total
a. Perform a chi-square analysis to determine if these genes are independently assorting. Remember to clearly state your hypotheses. Tell whether you would reject or accept your null hypothesis.
b. If the genes are not assorting, give a possible logical explanation as to why you think that the genes fail to assort.
2. A plant species X with n=5 chromosomes was crossed with a related species Y with n = 7 chromosomes. The F1 hybrids produced only a few pollen grains, which were used to fertilize the ovules of related species Z with n=7 chromosomes. A few plants were produced from this cross, and all had 19 chromosomes. The F1 hybrids (with 19 chromosomes) were mated with related species W with n=11 chromosomes. A few plants were produced from the cross and all had 30 chromosomes. Following self-fertilization of the F1 hybrids a few F2 plants were produced, each with 60 chromosomes. These plants were phenotypically different from either of the original species and were highly fertile.
a. Explain by diagram and description the events that produced these fertile F2 hybrids. You must be specific and very clear about what is happening
b. Give the karyotype of the gametes produced by the highly fertile F2 plants.
c. Using appropriate genetic terminology, tell what type of plant ultimately arises as a result of the above crosses.
3. A phenotypically abnormal individual has a phenotypically normal father with an inversion on one copy of chromosome 7 and a normal mother without any changes in chromosome structure. The order of genes along chromosome 7 in the father is as follows:
R T D M centromere P U X Z C (normal chromosome 7)
R T D U P centromere M X Z C (inverted chromosome 7)
The phenotypically abnormal offspring has a chromosome 7 with the following order of genes:
R T D M centromere P U D T R
With a sketch (complete), explain how the abnormal chromosome was formed. In your answer, explain where the crossover occurred (i.e., between which two genes). Also, give any other products that might have been formed as a result of the crossover you described. Assume that crossing over does not occur at the centromere.
Explanation / Answer
is test corss -----1:1:1:1
Observed
Expected
o-e
(o-e) 2 /e
orange pods, virus sensitive
160
100
60
36
green pods, virus resistant
165
100
65
42.3
orange pods, virus resistant
36
100
64
41
green pods, virus sensitive
39
100
61
37.2
total
400
156.5
The calculated chi square value is more than table value at 1% and 5% level of significance
So , reject null hypotheis and confirmed that the two gene are linked .
Observed
Expected
o-e
(o-e) 2 /e
orange pods, virus sensitive
160
100
60
36
green pods, virus resistant
165
100
65
42.3
orange pods, virus resistant
36
100
64
41
green pods, virus sensitive
39
100
61
37.2
total
400
156.5