Homologous and Homozygous – What is the Difference?
Homologous or homozygous? Let’s understand the difference in this post. We will start with homologous and move to homozygous because that would make it easy to understand.
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Homologous –
this term we use many times with reference to chromosome, isn’t it? Homologous chromosomes right! What this means is, in humans; as we are diploid organisms we have total of 46 chromosomes or 23 pairs. Half of these chromosomes come from mother (23 chromosomes) and half of these chromosomes come from father (23 chromosomes). That is how we have total of 46 chromosomes or 23 pairs of chromosomes.
Therefore, for every given pair, one chromosome is maternal and one chromosome is paternal (figure 1). Both these chromosomes in a pair would have the same genes which codes for the same traits. Even the location of all these genes would be same on both the chromosomes (because basically they are the same chromosome but coming from two parents).
Figure 1. Chromosome in pair having the same genes at same locations
Let’s say for example, we are talking about genes which codes for eye color and hair color. Figure 1 shows the position of both these genes on chromosome number 1. Whether it is a maternal chromosome 1 or paternal chromosome 1, these two genes are located on the same place for these chromosomes. This means for every given pair of chromosome, all the genes are same and their location is also same. That is why we call them homologous chromosomes.
Homologous Chromosome = Chromosomes in pair having the same genes (codes for same traits) at same locations (where ever it is present on maternal chromosome, it will be present in the same location on paternal chromosome).
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Homozygous –
as just discussed above, we are diploid organisms. This means we have two copies of every chromosome and thus we have two copies of every gene (figure 2). In one of our previous post we had seen that copies of the same gene are called alleles .
In short, alleles are different form of the same gene which might differ slightly in sequence giving us slightly different phenotype such as gene for eye pigmentation can give brown, green, blue etc. pigmentation.
Figure 2. Chromosome pair Homozygous for eye and hair color trait
Figure 2 shows gene for eye color. If both the chromosome 1, maternal as well as paternal codes for the same color eye pigment (blue) that means they have the same allele. In this case they are called homozygous for eye color trait. Let’s say for hair pigmentation both the chromosome 1 has allele for brown hair then they are called homozygous for hair color trait.
Homozygous = when on chromosome pair for a given trait both the alleles are same.
It is also possible that a given chromosome pair has two different alleles for the same gene, right! In that case they are called heterozygous for a given trait.
Remember, we use the term homozygous or heterozygous for individual gene. We cannot use it for the complete chromosome because a chromosome would have many different genes present and for each of them they might be either homozygous or heterozygous. Whereas homologous is the term we use with reference to chromosome in a pair.
I hope this post was helpful 🙂
To understand more details, watch a video on this topic here.