(a) Gene and allele.

Ans.A gene is a stretch of DNA or RNA that determines a certain trait. Genes mutate and can take two or more alternative forms; an allele is one of these forms of a gene. For example, the gene for eye color has several variations (alleles) such as an allele for blue eye color or an allele for brown eyes.

An allele is found at a fixed spot on a chromosome. Chromosomes occur in pairs so organisms have two alleles for each gene — one allele in each chromosome in the pair. Since each chromosome in the pair comes from a different parent, organisms inherit one allele from each parent for each gene. The two alleles inherited from parents may be same (homozygous) or different (heterozygotes).

(b) Genotype and phenotype.

Ans.Genotype and phenotype are very similar-sounding words that are related, but actually mean different things. The genotype is the set of genes in our DNA which is responsible for a particular trait. The phenotype is the physical expression, or characteristics, of that trait. For example, two organisms that have even the minutest difference in their genes are said to have different genotypes. These two mice may have different genotypes and both can still be white if they share the particular phenotype for white fur.

Comparisons of Genotype & Phenotype

Genotype Examples

Genotype is what makes the trait - the information within a gene, or the genetic makeup of a specific organism. Genotype is determined by the makeup of something called "alleles," a word that refers to the form of a gene that produces different effects.

Genotype is the information contained within two alleles. Genotype is the genetic makeup of an organism and it results in some of the physical characteristics of that organism.

Genotypes can only be determined by biological tests, not observations. Genotype is an inherited trait and hereditary information passed by the parents determines genotype. The entire genetic information about an organism is contained in a genotype – even those characteristics which are not expressed visually.

Examples of genotype are the genes responsible for:

eye color

hair color

height

how your voice sounds

certain diseases

certain behaviors

the size of a bird’s beak

the length of a fox’s tail

the color of stripes on a cat

the spots on a dog’s back

a person’s shoe size

Phenotype Examples

Phenotype is what you see - the visible or observable expression of the results of genes, combined with the environmental influence on an organism’s appearance or behavior. For example:

It is the expression of gene information which is observable with the senses (like the sound of a bird’s chirping or the color of a cat’s hair)

Phenotype can be determined by mere, simple observation. Examples of phenotypes are the actual visible characteristcs including:

Eye color

Hair color

Height

Sound of your voice

Certain types of disease

Certain behaviors

Size of a bird’s beak

Length of a fox’s tail

Color of the stripes on a cat

Size and shape of the spots on a dog’s back

An individual’s shoe size

With these examples, it is easy to see the difference between genotype and phenotype and to understand how these two concepts relate to each other. The next time you look at different traits that you have, or that you see