Question

What do you understand by a phenotype and a genotype? Explain by giving an example.

Answer 1

Hint: Phenotype (from Greek phenotype, meaning 'showing' and type, meaning 'type') is the term used in genetics for the composite characteristics or traits of an organism. Genotype is a complete set of hereditary genes or genes that can be passed down from parent to offspring.

Complete Answer:
(I) GENOTYPE: In biology, a gene is a DNA segment that encodes a trait. The exact arrangement of nucleotides (each made up of a phosphate group, sugar and base) in a gene can vary between copies of the same gene.
- As a consequence, a gene may occur in various forms across species. These multiple forms are known as alleles. The exact fixed position of the chromosome containing a particular gene is known as the locus.
- A diploid organism either inherits two copies of the same allele or a copy of two separate alleles from its parents. If a person inherits two identical alleles, their genotype is said to be homozygous in that locus.
- However, if they have two separate alleles, their genotype is known as heterozygous for that locus. Either autosomal dominant or recessive alleles of the same gene.The autosomal dominant allele will still be represented preferably over the recessive allele.
The following combination of alleles held by a person for a particular gene is their genotype.

EXAMPLE FOR GENOTYPE:
Let 's look at the classic example of eye colour.
- The gene encodes the colour of the eye.
- In this example, the allele is either brown or blue, with one inherited from the mother and one inherited from the father.
- The brown allele is dominant (B), the blue allele is recessive (b). If the infant inherits two separate alleles (heterozygous), they will have brown eyes. In order for the infant to have blue eyes, the blue eye allele must be homozygous.

(II) PHENOTYPE: The sum of the measurable characteristics of an organism is its phenotype. The main distinction between the phenotype and the genotype is that, although the genotype is inherited by the parents of the organism, it is not a phenotype.
Although the genotype is determined by the phenotype, the genotype is not identical to the phenotype.

The genotype affects the phenotype and variables, including:
Epigenetic alteration
Environmental factors and lifestyle factors

EXAMPLES OF PHENOTYPE:
- Environmental factors which can affect the phenotype include diet, temperature , humidity and stress.
- Flamingos is a prime example of how the climate affects the phenotype.
While famous for being vibrantly pink, their natural colour is white – the pink colour is caused by pigments in the species in their diet.
- A second example is the skin colour of a person. Our genes regulate the amount and form of melanin that we produce, but exposure to UV light in sunny climates causes the darkening of existing melanin and promotes increased melanogenesis and thus darker skin.

Note: The term genotype was coined in 1903 by the Danish botanist, plant physiologist and geneticist Wilhelm Johannsen.