Questions for Discussion:
1. What is the difference between dominant and recessive alleles?
Dominant alleles can be expressed phenotypically in the case of heterozygous and homozygous. In other words, it can be said that only one copy is present. While recessive alleles are only expressed if two copies are present.
2. a. What percentage of dominant traits are there in your class? Recessive?
The percentage of having dominant traits is 57. 8%. While the probability of having recessive traits is 42. 2%.
b. In a normal population, there's a ratio of about 3 dominant traits for every recessive trait for traits that follow Mendelian inheritance (75% dominant; 25% recessive). Explain why using the words genotype and phenotype in your answer.
Because according to Mendelian inheritance, when both of the parents' genotypes are heterozygous, the probability of having dominant phenotype is 75% and the probability of having recessive phenotype is 25%.
c. How do the class results compare to this ratio?
The probability of having recessive traits is larger than 25%.
d. Explain why they compare this way.
There are two reasons. The first one is there're only 18 students in our class so there may be a coincidence. If we investigate more people, we'll probably find that the probability of having recessive traits will get closer to 25%. The second one is there're also some traits like ACHOO syndrome which is a dominant trait but only a few people have it. Dominant traits are not always common. Thus, the probability of having dominant traits isn't as large as 75%.