Question

Define and explain the terms genotype and phenotype. Give an example of a genotype and phenotype; indicate how the genotype and phenotype are related. Define and explain what an allele is. Give an example of an allele and indicate how alleles are related to a genotype.

Answer 1

Defination:-

Genotype:-  Genotype of an individual refers to the sum total of genes inherited from both the parents irrespective of whether they are expressed or not.

Example:- TT, tt and Tt are genotypes for the size of stem in pure tall,dwarf,and hybrid tall garden pea.

Phenotype:- Phenotype of an individual refers to the expressed or observable structural and functional traits produced by the interaction of genes and environment.

Example:- Tallness in garden pea plant,colour blindness in man are phenotypes.Both are noticeble withe eyes.Blood group is phenotype that become evident after a special test.

Relation between Genotype and Phenotype:-

1) Individuals of the same genotype have the same phenotype and breed alike.Also individuals withe different genotypes may also have the same phenotype. For example:- The genotypes TT and Tt give rise to tall pea plants.

2) Individuals of the same phenotypes may or may not have the same genotype and may or may not breed alike. For example:- Phenotype tallness may have genotype TT or Tt, and will breed accordingly.

3) An individual's genotype is fixed at the time of fertilization, but in phenotype results from the interactions of all its genes with one another and with environmental factors.Phenotype may change with environment such as Skine becomes tannned on long exposure to the sun.

What is allele ?

A pair of genes that control the two alternative expressions of the same character and have the same loci (sites) in the homologous chromosomes were originally called alleles or allelomorphs.However, the term allele is used for any two genes of a single character.

Example:- The genes T and t for tallness and dwarfness are alleles for the height in garden pea according to original defination.Now, Tt,TT and tt areall considered alleles.

How alleles are related to a genotype:-

• Because they all talk about a characteristic of an organism.
• Alleles are different forms of a gene. For example, different ALLELES, for a trait such as eye color, are brown, blue, and green. These alleles (differnt forms of a gene) contribute to the genotype (the genetic makeup) of the living thing. The phenotype (physical characteristics) of the living thing are determined by the thing's genotype.
• An allele is a variant form of a gene. Some genes have a variety of different forms, which are located at the same position, or genetic locus, on a chromosome. Humans are called diploid organisms because they have two alleles at each genetic locus, with one allele inherited from each parent. Each pair of alleles represents the genotype of a specific gene. Genotypes are described as homozygous if there are two identical alleles at a particular locus and as heterozygous if the two alleles differ. Alleles contribute to the organism's phenotype, which is the outward appearance of the organism.
• The term "genotype" refers to the genetic makeup of an organism; in other words, it describes an organism's complete set of genes. In a more narrow sense, the term can be used to refer to the alleles, or variant forms of a gene, that are carried by an organism. Humans are diploid organisms, which means that they have two alleles at each genetic position, or locus, with one allele inherited from each parent. Each pair of alleles represents the genotype of a specific gene. For example, in sweet pea plants, the gene for flower color has two alleles. One allele codes for purple flowers and is represented by the uppercase letter F, whereas the second codes for white flowers and is represented by the lowercase letter f. A varied population of sweet pea plants could therefore feature three possible genotypes at this locus: FF, Ff, or ff. Each plant's genotype contributes to its phenotype, which, in this case, is the outward appearance of its flowers. A particular genotype is described as homozygous if it features two identical alleles and as heterozygous if the two alleles differ. The process of determining a genotype is called genotyping.