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Genotype and Phenotype – What is the Difference?

Genotype and Phenotype – What is the Difference?

To understand this topic we must know what are genes and alleles. We have already discussed these in one of the previous blog.

In brief genes are stretches or small sequences of DNA that codes for a particular trait. Alleles are different variants of the same gene which means they might have little difference in their sequence.

Such as we have hair color gene but all of us don’t have same hair color and that is because we carry different allele of the hair color gene.

Genotype:  In simple words it is what ‘we have’.

The complete genetic makeup of an individual or set of all the alleles that an individual possesses is called the genotype.  Set of genes or alleles in our DNA are responsible for a particular trait.

Let’s say for example eye color gene is coded by B and b where B is dominant; codes for brown color and b is recessive; codes for blue color. Since we are diploid we can have three different possible genotypes and that is homozygous dominant; BB or heterozygous; Bb or homozygous recessive; bb.

Genes are what are passed from one generation to another generation and that is why genotype is inherited.

So as we saw in above example we can have three possible genotypes and they would express something isn’t it? That expression or outcome of genotype is called phenotype.

Phenotype: In simple words it is what ‘we see’.

The physical appearance or expression of a particular trait or genotype is called phenotype. Most of the time it is the visible or observable expression of the genes. But phenotype also includes the biochemical properties because that also is a result of expression of particular genes.

Let’s take the eye color example again. Homozygous dominant BB genotype gives brown color phenotype. Heterozygous Bb gives brown color phenotype and homozygous recessive bb gives blue color phenotype.

Therefore, Genotype Determines the Phenotype.

If we put it in Punnett square as given below, it is easy to understand. We can have 3 different genotypes but they would express 2 different phenotypes.

I hope this post helps J

To understand more in detail, watch a video on this topic here.

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DNA, Gene, Chromosome and Genome – What is the Difference?

DNA, Gene, Chromosome and Genome – What is the Difference?

  • DNA:

It is a double helix structure. It has sugar phosphate backbone and it is made up of four nucleotides A, T, G and C.

In humans, the DNA is about 2 meters long and this much long DNA needs to fit in our tiny nucleus which is around 5-10 µm in size. So in order to fit inside the nucleus; DNA has a packaging strategy where it undergoes coiling by formation of nucleosome.

Figure 1. DNA

  • Gene:

In our 2 meters long DNA, there are segments or chunks of DNA i.e. specific nucleotide sequences around 100s of bp long which codes for specific proteins and RNA. These segments of coding DNA is called gene and we have about 20,000 genes spread across all the chromosomes.

Every gene has a specific site in our DNA. For example, cystic fibrosis gene is present on chromosome 7. The traits that we get from our parents is because of the genes that we get from them so traits passes from parents to child in the form of genes.

Figure 2. Gene

  • Chromosome:

As we just saw above that the DNA is too long to fit inside the nucleus. So it undergoes packing mechanism where the DNA starts wrapping itself around the histones proteins. This assembly where DNA is wrapped around histones is called nucleosome. Nucleosome formation condenses the DNA and therefore the space it requires to fit inside a nucleus would reduce. These nucleosomes would further undergo condensation by arranging them self in coiled form called chromosome.

So chromosome is nothing but super condensed form of DNA where it is wrapped around histone proteins. In humans, there are total of 46 chromosomes. We are diploid so that means 23 chromosomes comes from mother and 23 chromosomes comes from father; giving us total of 46 chromosomes or 23 pairs of chromosomes.

As saw above that DNA is about 2 meters long so when you take all the 46 chromosomes, unwind them and put them in one stretch that makes the 2 meters long DNA.

Figure 3. Chromosome

  • Genome:

A genome is organism’s complete set of DNA. This means the entire DNA present in a cell and for humans other than nuclear DNA; there is also DNA in mitochondria so it is all the nuclear DNA distributed over 24 chromosomes (22 autosomes and 2 sex chromosomes) and DNA in mitochondria. For example, if we are talking about plants we will take chloroplast DNA in consideration.

Since we are diploid, we have two copies of genome in nucleus because we have all the chromosomes in pair.

So when we put together all the genetic information present inside a cell; it becomes the genome of an organism.

So think of it this way that genome is huge book carrying lot of information and for easy access to this information; nature has divided it into 24 chapters (22 autosomes + 2 sex chromosomes). So genome is divided into 24 chromosomes.

Figure 4. Summary

I hope this helps 🙂

Watch a video on this topic here.