Heredity and Evolution: Hybridization

Heredity is the transfer of characteristics or the inheritance of traits from the parents to their offspring. A chromosome is a thread-like structure in the nucleus of a cell that carries the genetic materials. A gene is a small unit of DNA in the chromosomes responsible for a particular characteristic of an organism. The offspring developed may have similarities and dissimilarities with their parents. The differences in the traits of an offspring from the parents are known as variations. Genetic changes are the reason for these differences. We can acquire desired variations artificially, this is where hybridization comes into play.

The process of crossing genes or different genotypes of two organisms is known as hybridization.

  • Genotype: Genotype is the set of genes found in an individual. Ex: Genes responsible for the colour of the eye, complexion etc.
  • Phenotype: Phenotype is the all observable or expressed characteristics in an individual. Ex: Tallness or shortness, the colour of eyes, etc.

Let’s see how hybridization helps in variation with illustrations.

Consider two different alleles of a gene for tallness and shortness. Let’s denote them as ‘A’ for tallness and ‘a’ for shortness.

  • When we cross two tall plants that have alleles “AA” and “AA”, it results in a tall plant.

  • Again when we cross two dwarf plants that have alleles “aa” and “aa”, the hybrid plant produced will be short, having the “aa” gene. In this hybridization, a stable and short plant is produced.

Now, we will cross these two plants, one with its alleles as “aa” and the other one with “AA” alleles. In this case, the hybridization will result in a plant with the “Aa” gene. Here, the plant will be tall as the allele “A” dominant over the allele “a”.

This was Mendel’s experiment. Mendel, in his first hybrid experiment, took pea plants with tall and short characteristics and produced progeny from them. He observed the percentage of short plants and tall plants and found that all plants were tall.

The different possibilities of hybridization of different types of genes of plants can be explained by Punnett square. It is a simple table in which different types of gametes (sex cells with the given traits) of one parent are kept at one side of the table and those of the other are kept at the other side. Now the various possibilities are obtained and written inside the square blocks.


Heterozygous dominants are the ones that have different alleles, while homozygous are the ones that have similar dominant alleles.  To learn more about the hybridization of plants and Punnett square, watch the video.


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