What will be the exact color of a child’s eyes?
Or what trait will be more likely to be seen in the progeny?
Gregor Johann Mendel conducted experiments to come up with rules of inheritance that describe possible traits in each generation.
Let us understand the following terms before we look at the experiments and rules:
Phenotype
The phenotype of an organism is the whole set of characteristics or traits of that organism.
- This means, all the visible traits and the traits that can be made visible under suitable conditions make up the phenotype of the individual.
Genotype
The genotype of a person is the genetic makeup of that person.
- It is with reference to the information found in the individual’s cell .
- The genotype is distinct from the visible traits (phenotype) of the organism.
Allele
We discussed how each parent contributes to each gene.
- In the progeny, each trait is present in two alternative forms of a gene , each called an allele.
- For example - Tall-short, Blue Eyed-Brown Eyed, Blood group O or AB and so on.
- Each allele controls that single trait.
- Traits can be either dominant or recessive depending on the alleles.
- The genetic makeup of an allele (the gene that decides the flower colour) is the genotype.
- The physical appearance that results from the alleles (for example, the actual purple flower) is called the phenotype .
Representing alleles
The two alleles are represented using alphabets.
Example 1 - Let us take height of pea plant ;
- The two possible forms of alleles are Tall and Short .
- For convenience we take the alphabet corresponding to the ‘dominant’ trait .
- Here tall is the dominant trait; so we assign capital ‘T’ for the allele for tall phenotype.
- For the ‘recessive’ trait, we use the small letter of the same alphabet.
- So here small ‘t’ will be used to represent the allele for short phenotype .
Example 2 - Flower colour
Let us look at the example discussed in the previous section again,
Here if we assign;
- ‘P’ as the allele for the dominant trait that is purple colour flower ,
- ‘p’ will be assigned for the recessive trait, that is white colour flower.
