GENETICS: Mendelian Principles

Hi hivers, hope you are all doing well?
I have come with another interesting section on genetics. This will be a continuation of the previous post that I made. You can see the previous post here
In continuation of the work, we will be looking at the work of a great scientist called Gregor Mendel on genetics.

Genetics was first discovered by a scientist called William Bateson in 1905 but Gregor Mendel was considered as the father of genetics because he was able to explain some certain terms which the scientists before him could not do. Before Mendel came, geneticists are of the notion that a tall person that marry a short person will give birth to an offspring of average height. But when Mendel came and carried out his experiment on Pisum sativum (pea plant), he came to realize that characters do not actually blend but they are transfered as a discrete unit from parent to the offsprings.

After Mendel has done his work, other geneticists came and approved that he did a great job except that there are some amendments that need to be made to his work. This calls for the topic EXCEPTIONS TO MENDELIAN PRINCIPLES.

In contrary to Mendel's work, it has been proven that there are characters that can blend. An example of this can be seen in Mirabilis jalapa(four 0'clock flower).

four 0'clock flower: sourced from pixabay.com

In incomplete dominance which is one of the exceptions to Mendelian principles, two characters will blend together to produce another phenotype. For instance, in Mirabilis jalapa, when the red flower(RR) is crossed with white flower(rr), it will produce another phenotype which is pink(Rr).
According to Mendel, if we cross a red and a white flower, all the offsprings will be red phenotypically but here that does not happen. In incomplete dominance, none of them will be dominant over each other but there will be a blend between the two characters to produce a new one different from either of the parents.

image showing incomplete dominance in Mirabilis jalapa: sourced from wikimedia.org

Example in animal is a cross between black horse and white horse to produce a Andalusian horse.

andalusian horse: sourced from wikimedia.org

The next exception to Mendelian principle we will be looking at is Codominance. Codominance occurs when two versions, or 'alleles', of the same gene are present in a living thing, and both are expressed. Instead of one trait being dominant over the other, both traits appear. In codominance, there is no blend between the characters but rather each of the contributing character are well represented. For instance, a parent cat with a black eye is crossed with another one that has a yellow eye to produce an offspring that has both black and yellow on each of its eye.
An example in human is seen in the ABO blood system.

image showing codominance in human: sourced from wikimedia.org

REASONS WHY MENDEL USED PEA PLANT FOR HIS EXPERIMENT

Pea plant: sourced from wikimedia.org

To every action exhibited by Homo sapiens, there is definitely a reason behind it. That will make us to look at the reasons why Mendel choose Pisum sativum(Pea plant) out of the numerous plants we have in the universe for his experiment. Why didn't he choose mango tree instead of the pea plant, the reasons for this are stated below;

• Pea plant has a short life span.
• Pea plant is easy to cultivate.
• They are self-pollinating, and thus, self and cross pollination can easily be performed.
• They gave easily observed characteristics.

Conclusively, we are able to mention the work done by Mendel in genetics. Incomplete dominance and codominance are the exceptions to Mendelian principle as stated above. Mendel used pea plant for his experiment and the reason why he used it has been discussed.

I will like to stop here for now. Hope you've learnt something new today? Have a blissful day and don't forget to stay safe.

HINTS

• Geneticist is a person who studies genetics.
• Offspring: an animal or plant progeny; young ones.
• Character and trait are the same in genetics.

References

Introduction to genetics
Mendel's genetics