CBSE Questions for Class 12 Medical Biology Evolution Quiz 13 - MCQExams.com

• Hardy-Weinberg's principle gives the geneticists a tool to determine when evolution is occurring. 
• Geneticists use this principle to calculate a starting point allele frequency and this frequency is then compared with the frequencies measured at some future point. 
• The degree of evolutionary change is determined by calculating the difference between the observed frequencies and frequencies based on this principle.

• 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:
  

• The carboniferous period lasted from about 350 million years ago. It generally had a more uniform, tropical, and humid climate, was favorable for living organisms like amphibia, thus called the "age of amphibians".
• Silurian is a period of origin of jawed fishes, wingless insects, scorpions, and ferns.
• Ordovician is called the "age of invertebrates".
• Cambrian is called the "age of trilobites".
• In jurassic period, gymnosperms and dinosaurs are abundant.

The Hardy-Weinberg equation is expressed as p² + 2pq + q² = 1, where p is the frequency of the "A" allele and q is the frequency of the "a" allele in the population. In the equation, p² represents the frequency of the homozygous genotype AA, q² represents the frequency of the homozygous genotype aa, and 2pq represents the frequency of the heterozygous genotype Aa. In addition, the sum of the allele frequencies for all the alleles at the locus must be 1, so p + q = 1. So if the frequency of an allele A is 0.7, then the frequency of allele a is 0.3. Therefore according to formula: (0.7)² + 2Aa + (0.3)² = 1 

0.49 + 0.9 + 2Aa = 1

Aa = 0.42 (2Aa represents genotype frequency of genotype Aa). Hence option B is correct.

• The Hardy-Weinberg equilibrium is a principle stating that the genetic variation in a population will remain constant from one generation to the next in the absence of disturbing factors.
• For instance, mutations disrupt the equilibrium of allele frequencies by introducing new alleles into a population. 
• There are five basic Hardy-Weinberg assumptions: no mutation, random mating, no gene flow, infinite population size, and no selection.
• Hence, Hardy-Weinberg equilibrium is known to be affected by gene flow, genetic drift, mutation, genetic recombination, and natural selection.

• Genetic drift is the random change in the frequency of alleles in a population due to chance events causing unequal participation of individuals in producing succeeding generations. 
• Genetic drift can be a principal force in the evolution of some populations; it is especially associated with populations of small size.
• The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces.

• The rate of appearance of new forms is linked to the life cycle or the life span.
• Microbes that divide fast have the ability to multiply and become millions of individuals within hours. 
• A colony of bacteria (say A) growing on a given medium has built in variation in terms of ability to utilize a feed component. 
• A change in the medium composition would bring out only that part of the population (say B) that can survive under the new conditions. 

• In due course of time this variant population outgrows the others and appears as new species. 
• This would happen within days. For the same thing to happen in a fish or fowl would take million of years as life spans of these animals are in years.