an organism's genotype is its specific combination of alleles for a given gene

What is meant by this? Is it talking about heterozygous and homozygous (like GG or Gg) or is it talking about the nuclear bases?


  • $\begingroup$ I'm voting to close this question as off-topic because there is no source given for the fragment quoted. $\endgroup$
    – David
    Apr 12, 2018 at 17:49

2 Answers 2


From wikipedia

An Allele is a variant form of a given gene.

Let's consider a simplified example. There is a gene for eye color and there are different alleles at this gene. The allele for blue eye, the allele for brown eye etc...

In a diploid (see ploidy) individual (humans are diploid), we have two copies of each gene (exception of sex chromosomes). Let's imagine, at a givne gene, there are 3 possible alleles called A, B and C. The possible combinations are


The genotype of an individual for a given gene (I should say locus for the sake of generality) is called the genotype of an individual.

Is it talking about heterozygous and homozygous[?]

The terms "homozygous" or "heterozygous" are adjectives to define whether, in a diploid genotype, the same allele is found on both haplotypes or not. In the above examples, 3 genotypes are homozygous (AA, BB and CC) and 3 genotypes are heterozygous (AB,AC and BC).

[I]s it talking about the nuclear bases?

For two alleles to be different, they must differ in their sequence of nuclear bases of course.


Alleles are different versions of the same gene; they have different nucleotide sequences. Which versions of each gene an organism gets defines its genotype.

Zygosity (heterozygous/homozygous) is a related idea. When creatures have more than one copy of a chromosome (e.g. one from each parent) the alleles of each gene on each chromosome may be the same (homozygous) or different (heterozygous).


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .