The sorghum plant homozygous for three recessive alleles is 30 cm tall, and homozygous for the dominant alleles is 50 cm. 192 plants were obtained in F2. How many of them will have a genetically determined height of 44 cm?
Let’s designate the recessive genes that determine the height of the sorghum plant as f, g and h, then the dominant alleles of the genes of this trait will be designated as F, G and H.
The sorghum plant homozygous for three recessive alleles has the ffgghh genotype and is capable of producing only one type of germ cells – fgh.
The sorghum plant homozygous for dominant genes has the FFGGHH genotype and also produces only one type of germ cells – FGH.
All offspring from crossing these plants will be genetically and phenotypically homogeneous. All plants will be represented by FfGgHh heterozygotes. All of them will have a genetically determined height of 44 cm.
These hybrids produce eight types of germ cells – FGH, FgH, Fgh, fGH, Fgh, fGh, fgH, fgh.
Crossing such plants with each other is capable of producing 64 variants of the genotype in the offspring and splitting according to the phenotype in a ratio of 27: 9: 9: 9: 3: 3: 3: 1.
Genotypes corresponding to a sorghum height of 44 cm – 9 out of 64.
(192 * 9) / 64 = 27.
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