Using experimental data on genetic analysis of introgressive lines for the character «hairy leaf sheath» controlled by the «cuckoo» chromosome 4Sl, the algorithm for calculation the theoretical segregation ratio in F2 was developed. Segregation distortion is caused by non-viability of the majority of gametes lacking the chromosome 4Sl. The frequency of functioning gametes without the chromosome 4Sl is determined by the probability p versus the theoretically expected ratio 7 nonviable : 9 viable ones. Since segregation involves two characters, gamete viability and hairiness, the ratio 15 hairy : 1 hairless was used as a base for search of the frequency p by maximum-likelihood method using 16 populations F2 from crossing the lines differing in the character studied.
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