Our Take on Genotypes and Phenotypes

Genotypes and Phenotypes are two types of DNA.


We’ve recently received a lot of inquiries on the link between DNA test results and features like blood type and eye color. The link between genotypes and phenotypes holds the key. Genotypes are the A’s, T’s, G’s, and C’s in your DNA that you got from your parents. The traits that we can see as a result are called phenotypes. Let’s start with phenotypes, which are easier to understand.


The phenotype


In general, a phenotype is an inherited characteristic that we notice. Phenotypes include eye color, hair color, and blood type. You may have a brown-eye phenotype, which means your eyes are brown; a brown-hair phenotype, which means your hair is brown; or an A blood type phenotype, which means your blood type is A.


the genotype


The DNA that codes for the phenotypic is called a genotype. Have you ever considered how a person may have a blue-eyed parent and a brown-eyed parent yet only have brown eyes? How can a person have only one pair of eyes when their DNA is acquired from both parents?


Parents do not pass down eye color to their children; instead, they pass down an allele. Your genotype is made up of the alleles from your mother and father together. Your genotype determines your phenotype, or the trait that we can see. The child’s genotype will be blue-brown, and his or her phenotype will be brown, if the blue-eyed parent handed down a blue allele and the brown-eyed parent handed down a brown allele. How can we know the infant will have brown eyes?




Some alleles are dominant, whereas others are recessive. Blue is a recessive gene in this situation, while brown is dominant. You are heterozygous for a characteristic if you inherit distinct alleles from each parent.


You are homozygous for a characteristic if you inherit the same allele from both parents. (See DNA Basics Chapter 4: A Glossary of Terms for a review of terminology.) Due to the fact that blue is recessive and brown is dominant, any blue-brown heterozygote will almost certainly have a brown-eye phenotype, with brown eyes.


You can use a tool called a Punnett square to map the genotypes and traits you could inherit from your parents. Upper case letters are traditionally used to denote dominant alleles, whereas lower case letters are used to denote recessive alleles. A Punnett square depicting the genotypes for a person with a homozygous blue-eyed parent and a heterozygous brown-eyed parent is shown below.


Punnett square illustrating the genotypes and traits that can be inherited from a homozygous blue-eyed parent and a heterozygous brown-eyed parent.


Only the blue allele may be passed down from a homozygous blue-eyed parent. The blue or brown allele can be passed down from a heterozygous brown-eyed parent. Children with a blue allele and a brown allele, or a blue-brown genotype, will have brown eyes and a brown-eye phenotype. Similarly, children who inherit two blue alleles, i.e., a blue-blue genotype, would have blue eyes and a blue-eye phenotype.


Dominance by two people


Because A and B are co-dominant, determining blood type is more difficult. O is a recessive gene. A parent with type O blood can only pass on an O allele, just like a blue-eyed parent can only pass on a blue gene. An A heterozygote (AO) can pass on either an A or an O, but an AA homozygote may only pass on an A.







Here’s a rundown of blood type inheritance options:

Parent 1’s allele Parent 2’s allele The Genotype Heterozygote or homozygote ? The Phenotype
A A AA homo A
A O AO hetero A
A B AB hetero AB
B B BB homo B
B O BO hetero B
B A AB hetero AB
O O OO homo O
O A OA hetero A
O B OB hetero B




A chart depicting the inheritance patterns of blood types. It’s worth noting that the order of alleles within a genotype has no bearing; for example, AB and BA are the same genotype.


People of different ethnicities


You don’t require a DNA test to determine your eye color in the case of eye color! You can tell whether you have brown eyes by looking in the mirror. Your genotype is something you can’t see in the mirror. Similarly, though you may have certain features associated with particular ethnicities, a DNA test is the only method to determine all of the ethnicities in your DNA that you acquired from your parents.


You can see that two persons with the same parents can have different eye colors, and two individuals with the same parents can have distinct ethnicities, just as you can see in the Punnett square above.