
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
Rice is a diploid plant with a chromosome composition of 2n=24. If a pair of homologous chromosomes in a somatic cell has an extra chromosome, making three in total, it is called trisomic rice. During meiosis of trisomic rice, homologous chromosomes separate randomly, producing two types of gametes: one is the n+1 type, which contains two of the homologous chromosomes, and the other is the n type, which contains one of the homologous chromosomes. The egg cell of the n+1 type is fertile, while the pollen is sterile.  
(1) From the perspective of variation type, the formation of trisomic rice belongs to ___, and the reason for its formation is the failure of a pair of homologous chromosomes to separate during the late stage of the first meiotic division, moving towards the same pole, or the failure of a pair of sister chromatids to be distributed to two daughter cells during the late stage of the second meiotic division.  
(2) It is known that the fragrance in rice (b) is a trait produced by a recessive mutation. By crossing ordinary rice with trisomic rice (such as trisomy 7), it is possible to determine whether the alleles (B, b) are located on chromosome 7. Now, using homozygous non-fragrant ordinary rice (BB) as the male parent and trisomic rice with fragrance (female parent) for crossing, trisomic plants are selected from F<sub>1</sub> as the male parent, and crossed with fragrant ordinary rice (bb) to obtain F<sub>2</sub>. Analysis shows:  
If the alleles (B, b) are located on chromosome 7, the phenotypic ratio in F<sub>2</sub> is ___.  
If the alleles (B, b) are not located on chromosome 7, the phenotypic ratio in F<sub>2</sub> is ___.

Present the answer in LaTex format: \boxed{Your answer}
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