What is genetics? Genetics is the study of inheritance. The fact that the offspring of any species resemble the parents indicates that the characters in the parents are passed on to the offspring.
Factors that determine characters (genes) are passed on from parent to offspring through gametes or sex cells.
In fertilization the nucleus of the male gamete fuses with the nucleus of the female gamete. The offspring show the characteristics of both the male and the female.
Genetics is the study of how this heritable material operates in individuals and their offspring.
Variations within Plant and Animal Species
- The term variation means to differ from a standard.
- Genetics also deals with the study of differences between organisms belonging to one species.
- Organisms belonging to higher taxonomic groups e.g. phyla or classes are clearly different.
- Although organisms belonging to the same species are similar, they show a number of differences or variations such that no two organisms are exactly the same in every respect.
- Even identical twins, though similar in many aspects, are seen to differ if they grow in different environments.
- Their differences are as a result of the environment which modifies the expression of their genetic make-up or genotype.
- The two causes of variations are the genes and the environment.
- Genes determine the character while the environment modifies the expression of that character.
Continuous and Discontinuous Variation
What are continuous variations? There are the differences between the individual are not clear-cut. There are intermediates or gradations between any two extremes.
Continuous variations are due to action of many genes e.g. skin complexion in humans.
In continuous variation, the environment has a modifying effect in that it may enhance or suppress the expressions of the genes.
Continuous variation can be represented in form of a histogram.
Example of continuous variation in humans is weight, height and skin complexion.
In humans, height shows gradation from tall, to tallest.
So does the length of mature leaves of a plant.
In most cases, continuous variation is as a result of the environment.
What are discontinuous variations? These are distinct and clear cut differences within a species.
- Ability to roll the tongue.
- An individual can either roll the tongue or not.
- Ability to taste phenylthiourea (PTC); some individuals can taste this chemical others cannot.
- Blood groups – and individual has one of the four blood groups A, B AB or O.
- There are no intermediates.
- Albinism – one is either an albino or not.
- Discontinuous variations are determined by the action of a single gene present in an individual.
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