Which one of the following statements about variations is not true ?
All variations in a species have equal chances of survival.
Understanding Variations in Biology
Variations are the differences found between individuals of the same species. These differences can be in appearance, behaviour, or even genetic makeup. Variations are fundamental to the process of evolution.
Analyzing Statements About Variations
Let's carefully examine each statement provided in the options to determine which one is not true regarding variations.
- Statement 1: Variation is minimum in asexual reproduction.
Asexual reproduction involves a single parent producing genetically identical offspring (clones). Variations in asexual reproduction primarily arise only through random mutations. In contrast, sexual reproduction involves the combination of genetic material from two parents, leading to greater genetic diversity and thus more variation among offspring. Therefore, it is true that variation is generally minimum in asexual reproduction compared to sexual reproduction.
- Statement 2: All variations in a species have equal chances of survival.
This statement relates to natural selection, a key mechanism of evolution. The environment plays a crucial role in determining which variations are advantageous for survival and reproduction. Variations that provide an individual with a better ability to survive and reproduce in a particular environment are more likely to be passed on to the next generation. Conversely, variations that are disadvantageous reduce the chances of survival and reproduction. Thus, different variations have unequal chances of survival depending on the environmental conditions. This statement is not true.
- Statement 3: Changes in genetic constitution result in variation.
Genetic constitution, or genotype, refers to the set of genes an individual possesses. Variations arise due to differences in these genes. Changes in the genetic material, such as mutations (alterations in DNA sequence) or the recombination of genes during sexual reproduction, directly lead to changes in the genetic constitution and result in phenotypic variations (observable differences). This statement is true.
- Statement 4: Variants can be selected by environmental factors.
Environmental factors, such as climate, availability of food, presence of predators, and diseases, act as selective pressures. Individuals with variations that make them better suited to these environmental conditions are more likely to survive and reproduce, passing on those advantageous variations. This process is natural selection. This statement is true.
Based on the analysis, the statement that is not true about variations is that all variations in a species have equal chances of survival.
Summary of Statements
| Statement | Truth Value | Explanation |
|---|---|---|
| Variation is minimum in asexual reproduction. | True | Offspring are genetic clones; variation mainly from mutation. |
| All variations in a species have equal chances of survival. | False | Survival depends on environmental selection pressures. |
| Changes in genetic constitution result in variation. | True | Mutations and recombination alter genes, causing variation. |
| Variants can be selected by environmental factors. | True | Natural selection acts on variations. |
Revision Table: Key Concepts in Variations
| Term | Definition | Relevance to Variation |
|---|---|---|
| Variation | Differences among individuals of the same species. | The subject of study. |
| Genetic Constitution (Genotype) | The set of genes an organism possesses. | Changes here lead to variation. |
| Mutation | A permanent change in the DNA sequence. | A source of new variation. |
| Recombination | Mixing of genetic material during sexual reproduction. | Increases variation in sexually reproducing organisms. |
| Natural Selection | Process where environmental factors favour certain variations. | Determines which variations survive and are passed on. |
| Asexual Reproduction | Reproduction from a single parent, producing clones. | Results in minimal variation. |
| Sexual Reproduction | Reproduction involving two parents and genetic mixing. | Results in significant variation. |
Additional Information on Survival and Variations
The concept that not all variations have equal chances of survival is central to evolutionary biology. This principle is known as differential survival and reproduction. Consider an example: In a population of rabbits, some might have thicker fur (a variation). If the environment becomes colder, rabbits with thicker fur are more likely to survive the cold, find mates, and reproduce, passing on the 'thick fur' variation. Rabbits with thinner fur might be less likely to survive and reproduce in the cold. Over generations, the 'thick fur' variation becomes more common in the population because it was favoured by the environmental factor (cold temperature). This illustrates how variations have unequal survival chances and how environmental selection shapes the genetic makeup of a species over time.
Variations are the raw material for evolution. While mutations introduce new variations, and sexual reproduction shuffles them, it is the interaction with the environment (selection) that determines which variations persist and become prevalent in a population.
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