(2) In the fourth cell, the centromere of C cell divides and contains no homologous chromosomes, so the cell is in the late stage of meiosis.

(2) In the mathematical model of 42, the reason of bc fragment formation is centromere division and chromatid separation, which leads to the doubling of chromosome number. According to 4, it can be judged that normal somatic cells of organisms contain 7 chromosomes, so the value of m in 42 is 2.

(3) The relative variation curve of DNA molecular number of 3)C ~ F segment cells is as follows:

(7) Animals with AaEeTt genotype mate with recessive individuals, and the ratio of phenotypic straight hair, straight hair, curly hair and curly hair is 9: lower: lower: 9, in which straight hair and curly hair belong to recombination, and straight hair and curly hair belong to parent combination, so the exchange value = recombination number ÷ (recombination number

So the answer is:

(2) After the second meiosis

(2) Centromere division 2

(3)

(7) less than 0%? 70%