krit.club logo

Genetics and Evolution - Evolution

Grade 12ICSEBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

•

Origin of Life: The Oparin-Haldane hypothesis states that life originated from non-living organic molecules. The Miller-Urey experiment simulated primitive earth conditions (CH4,NH3,H2,H2OCH_4, NH_3, H_2, H_2O vapor and electric discharge) to produce amino acids.

•

Hardy-Weinberg Principle: Allele frequencies in a population remain constant from generation to generation in the absence of evolutionary influences like mutation, gene flow, genetic drift, and natural selection.

•

Homologous Organs: Structures with the same embryonic origin and basic structure but different functions (e.g., the forelimbs of humans, cheetahs, whales, and bats). This indicates Divergent Evolution.

•

Analogous Organs: Structures that perform similar functions but have different anatomical origins (e.g., wings of butterflies and birds). This indicates Convergent Evolution.

•

Adaptive Radiation: The process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography (e.g., Darwin's Finches and Australian Marsupials).

•

Genetic Drift: A random change in allele frequencies over generations, which is more pronounced in small populations. Examples include the Founder Effect and the Bottleneck Effect.

•

Modern Synthetic Theory of Evolution: This combines Darwin's Natural Selection with Mendelian Genetics, identifying that variations are caused by mutations, gene recombination during meiosis, and DNADNA replication errors.

📐Formulae

p+q=1p + q = 1

p2+2pq+q2=1p^2 + 2pq + q^2 = 1

Frequency of dominant phenotype=p2+2pq\text{Frequency of dominant phenotype} = p^2 + 2pq

💡Examples

Problem 1:

In a stable population at Hardy-Weinberg equilibrium, the frequency of the recessive allele (qq) for a particular trait is 0.30.3. Calculate the percentage of the population that is heterozygous (2pq2pq).

Solution:

Given q=0.3q = 0.3. Using the formula p+q=1p + q = 1, we find p=1−0.3=0.7p = 1 - 0.3 = 0.7. The frequency of heterozygotes is given by 2pq2pq. Therefore, 2×0.7×0.3=0.422 \times 0.7 \times 0.3 = 0.42.

Explanation:

To find the percentage, multiply the frequency by 100100: 0.42×100=42%0.42 \times 100 = 42\%. This means 42%42\% of the population carries both the dominant and recessive alleles.

Problem 2:

Explain why the wings of a bat and the wings of a butterfly are considered analogous structures.

Solution:

Bat wings are composed of bony skeletal elements covered by skin (patagium), while butterfly wings are composed of chitinous membranes supported by veins. They do not share a common evolutionary origin.

Explanation:

Because they have different anatomical structures and embryonic origins but perform the same function (flying), they are the result of convergent evolution, which classifies them as analogous structures.

Evolution - Revision Notes & Key Diagrams | ICSE Class 12 Biology