Question

Be able to determine the possible genotypes based on a person’s phenotype. (For example: Suppose a person expresses tongue-rolling, a dominant trait, in his phenotype. What are his/her possible genotypes?)

Answer 1

Let assume that the allele which is responsible for toungue rolling is completely dominant over the allele that inhibit the toungue rolling. It is an example of complete dominance.

Let assume the toungue rolling is occured due to the presence of an allele T. And non toungue rolling is caused by an allele t

Hence toungue rolling is dominant , so the T allele will also domanint to non toungue rolling allele t.

Now let assume a toungue rolling person has a genotype of TT which is homozygous dominant. And a non toungue rolling person has a genotype of tt which is homozygous recessive.

Now make a cross of them

TT X tt

T t -------> gamets

Tt -------> F1

Here T will completely dominate the expression of t , and the offspring will be a toungue rolling organism due to presence of one dominant allele T.

So the possible genotype of the person will either TT or Tt.

now if in place of dominant trait , a recessive trait is given and provide that it is recessive to another trait we can easily make the genotype of the organisim.

So if phenotype is given with the data wheather it is recessive or dominant we can make the genotype.