Differences between Phenotype and Genotype

 

Phenotype

•     Phenotype is a term used in genetics to refer to all the observable traits in organisms as a result of the interaction of the genotype with the environment.

•     The term ‘pheno’ in ‘phenotype’ refers to ‘observe’ and thus phenotype is used to indicate the observable characteristics in organisms like its height and color.

•     The phenotype of an organism covers the organism’s morphology, physical form and structure, its development and behavior, its biological and physiological properties, and even the products of the organism.

•     The phenotype of an organism is dependent on two factors; the expression of the genome or its genotype and its interaction with the environmental factors.

•     Either one or both factors might act to bring about the phenotype of an organism.

•     Variation in phenotype is observed even within an individual because of environmental, physiological, and morphological changes associated with age.

•     The variation in phenotype forms the basis of natural selection where the environment favors the survival of more fit individuals over the others.

•     This phenomenon is clearly seen in the case of twins, where individuals with identical genotypes might express different phenotypes if each individual encounters a different environment.

•     Thus, without phenotypic variation, evolution by natural selection wouldn’t be possible.

•     The concept of variation in phenotype might act below the genetic makeup of the individual. An example of this is the silent mutations that do not change the amino acid sequences but change the frequency of guanine-cytosine base pairs.

•     This change affects the G-C content of the genome, which, in turn, causes an increase in thermal stability, allowing the organism to live in high-temperature environments.

•     Examples of phenotypes seen in various organisms include the blood group, eye color, and hair texture as well as genetic diseases in humans, pod size and color of leaves, beak birds, etc.



Genotype

•     The genotype is a term used in genetics used to refer to the genetic composition of an individual consisting of heritable genes.

•     The term ‘genotype’ also refers to the two alleles that are inherited for a particular gene.

•     Genotypes are represented with alphabetical letters like Bb where B stands for the dominant allele and b stands for the recessive allele.

•     The physical characteristics of an individual, called phenotypes, are a result of the expression of these genes.

•     However, the genotype is not the only factor responsible for the difference in the phenotype, and phenotype is also affected by other factors like inherited epigenetics and environmental factors.

•     Thus, neither all individuals with the same genotype look identical nor all individuals that look-alike has the same genotype.

•     Genotypes in organisms are affected by various factors like mutations that change the frequency of the base pairs or the structure of the DNA sequences.

•     However, genes formed due to somatic mutations that are acquired rather than inherited are not considered as the genotype of the individual. These mutations also do not bring about any changes in the genotypes.

•     The expression of genotypes in organisms is dependent on the composition of the genotype. In the presence of a dominant allele, the offspring for sure inherits the dominant traits irrespective of the other allele.

•     The genotype of a character depends entirely on the gene sequences except for the occasional heritable mutations.

•     Thus, genotype remains the same throughout the life of an individual unless affected by mutations.

•     Similarly, phenotypic changes in an individual don’t cause any changes in the genotype of the individual as genotypic is not affected by phenotype.

•     Genotypes, like phenotypes, are not observable from the outside. Instead processes like genotyping are to be performed.

•     The process of determining the genotype of an individual is termed genotyping, which can be used for various purposes like PCR, DNA sequencing, and restriction fragment length polymorphism (RFLP).

•     Examples of genotypes seen in different animals include TT as the homozygous allele for height, Tt for the heterozygous allele for height, and BB for homozygous allele for eye color.

 



Examples of phenotype



Melanin production

•     Melanin production in humans is controlled by particular genes; thus, the difference in melanin production is due to the differences in the genotype of the organisms.

•     Although different genes control the distribution of melanin throughout the body, there is a single gene that affects its production.

•     Thus, individuals with a particular genotype might suffer form no production of melanin at all, resulting in albinism.

•     Thus, people with albinism usually have white or some shade of pink colored skin.

•     Albinism is a phenotype resulting from a particular genotype, and because the gene pool for albinism is rather large, cases of albinism are seen in many populations.

•     Albinism might even be prevalent in some animals.

Mendels’ Peas

•     Mendel studied a number of phenotypes in peas as a part of his studies. Almost all discoveries he made were based on those phenotypes.

•     In the case of the color of the peas, green and yellow-colored peas were studied. He found that breeding of yellow and green-colored peas resulted in half yellow and half green peas with some variation in some generations.

•     Based on this, he determined the ratios of different phenotypes in different generations.

•     The coloration in peas is coded by a particular gene which results in yellow color. In the absence of this gene, the color of the pea turned green.

•     Thus the yellow color is the dominant allele, and the green is the recessive allele.

Examples of genotype

Eye color

•     The dominant genetic trait for eye color is brown, which is represented by BB genotype.

•     Thus, in homozygous individuals, the genotype for eye color will be BB or bb.

•     All other eye colors ranging from blue to green to grey are recessive traits that are only expressed when the genotype is homozygous-recessive, bb.

•     If the genotype is homozygous, the genes for eye color in the loci of the two chromosomes should be identical.

•     The phenotype of the individual, that is, the eye color in the individual is dependent on the resultant genotype for that character.

Curly hair

•     If we consider the genotype for hair type as H for dominant trait and h for a recessive trait, the genotype for curly hair would be HH or Hh.

•     This genotype codes for the protein that causes the hair to be curly.

•     If the genotype is HH, the individual would have curly hair, but in the presence of a heterozygous genotype, the hair would be wavy, which is between curly and straight hair.

•     For the hair to be straight, the genotype would have to be hh as straight hair is a recessive trait.

•     In complete dominance, the curly hair trait is observed in individuals with the heterozygous condition.