Test: Evolution-3 - NEET MCQ

Stabilising selection favours average sized individuals whereas eliminates small sized individuals. It reduces variation and thus does not promote evolutionary change. But, it maintains the mean value form generation of generation. In directional selection, the population changes towards one particular direction. It favours small or large sized individuals and more the mean size of the population changes. Disruptive in eliminates most of members with mean expression, so may lead to developemnt of two different individuals. it is important in bringing about evolutionary change.

When more individuals of a population acquire a mean character value, it is called stabilising selection. No change in allelic frequency in a population will lead to Hardy-Weinberg equilibrium.

When migration of a section of population to another place and population occurs, gene frequencies change in the original as well as in the new population. New genes/alleles are added to the new population and these are lost from the old population. There would be a gene flow if this gene migration, happens multiple times. If the same change occurs by chance, it is called genetic drift. Sometimes the change in allele frequency is so different in the new sample of population that they become a different species. The original drifted population becomes founders and the effect is called founder effect.

In a stable population, for a gene with two alleles, 'A' (dominant) and 'a' (recessive), if the frequency of 'A' is p and the frequency of 'a' is q, then the frequencies of the three possible genotypes (AA, Aa and aa) can be expressed by the Hardy-Weinberg equation:
p² + 2pq + q² = 1
where p² = Frequency of AA (homozygous dominant) individuals
q² = Frequency of aa (homozygous recessive) individuals
2pq = Frequency of Aa (heterozygous) individuals
so, p = 0.6 and q = 0.4 (given)
∴ 2pq (frequency of heterozygote)
= 2 × 0.6 × 0.4
= 0.48

The development of melanin pigment in moth occurred due to mutation. The light coloured form of peppered moth gave rise to the dark coloured form by mutation.

Once inter-breeding population of finches, now have failed to produce fertile F₁ hybrids, this means they have now formed two distinct species.

Isolation is the prevention of mating amongst inter breeding groups due to physical (e.g., geographical, ecological) and biotic (e.g., physiological, behavioural, mechanical, genetic) barriers. Reproductive isolating mechanisms are the biological properties of individuals which prevent the interbreeding of naturally sympatric populations. It maintains the characters of the species but can lead to the origin of new species. Also, Darwin considered that useful variations are transmitted to the offspring and appear more prominently in succeeding generations. After some generations these become continuous and gradual variations in the possessor would be so distinct that they form a new species.

Statement 1 is correct: Evolution by natural selection began with differences in metabolic capabilities of early cellular life.
Statement 2 is incorrect: The rate of appearance of new species is slower in organisms with longer life spans, not faster.
Statement 3 is correct: Fitness is based on inherited characteristics that allow an organism to adapt and be selected by nature.
Statement 4 is correct: Lamarck believed evolution occurred through the use and disuse of organs, such as giraffes elongating their necks.

Darwin's Theory of Evolution (1) is associated with natural selection, which is the process of gradual change in species through survival of the fittest (C).
Lamarck's Theory of Evolution (2) is the idea that acquired characteristics (such as a giraffe's neck elongating) are passed down to offspring (A).
Fitness in Evolution (3) refers to an organism's ability to survive and reproduce based on inherited traits (D).
Natural Selection (4) refers to the process where variations that provide better adaptation to the environment are selected over time (B).

Gene migration or gene flow (1) involves the movement of genes between populations, affecting gene frequencies.
Genetic drift (2) refers to random changes in gene frequencies due to chance events, especially in small populations.
Mutation (3) introduces new genetic variations that can alter gene frequencies.
Genetic recombination (4) during gametogenesis creates new combinations of alleles, influencing genetic diversity.
Natural selection (5) acts on heritable traits, enhancing reproductive success and influencing the frequency of advantageous alleles in future generations.
All these factors contribute to changes in allele frequencies and can lead to speciation over time.