Life sciences, genetics, gene expression / principles and exploration
Mendelian monohybrid crosses — principles and investigation
In Mendel's pair trait crosses, we look at the probability of passing alleles from both parents to their offspring. Change the parent genotype and number of offspring and compare the theoretical phenotypic ratio with the actual sample. Dominant does not mean more common or better.
How does it work?
Theory ratio is probability. Small samples can deviate significantly, and even large samples are not guaranteed to be exactly 75%. Dominance does not mean that it is common or excellent.
Yy × Yy → YY:Yy:yy = 1:2:1 → Yellow:Green = 3:1
Try this investigation
- Select the parent genotype and fill in the Punnett square yourself. When executed, descendants are created with random numbers from the same seed.
- Record 10 and 1000 of Yy×Yy with the same seed and compare them with the theoretical ratio.
- In a small sample, only the seed is changed, and in other records, only the parent is changed to yy for comparison.
Interpreting your results
What is the theoretical genotype ratio and phenotype ratio of Yy×Yy?
Four different combinations YY, Yy, Yy, yy have the same probability. Yy is also yellow, so the phenotype is 3:1. Dominance does not mean that it is common or excellent.
Assumptions and limitations
Assume that the color-determining gene Y/y is completely dominant and that the offspring are independent with the same probability of fertilization and survival. It does not explain all the characteristics of actual peas. Association, environment, penetrance, and natural selection are omitted. If the random number seeds are the same, the results with the same number of parents and samples are reproduced.