Q.What is biological evolution? Elucidate three evidences of biological evolution with examples.
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Start your 14-day free trial to unlock the full solution →Biological evolution is descent with heritable modification across generations, supported by morphological, fossil and embryological evidence.
What is biological evolution? Biological evolution is the slow, continuous, and heritable change in the genetic composition and characteristics of populations of organisms over successive generations, through which new species arise from pre-existing ones by descent with modification, driven by mechanisms such as natural selection, mutation, genetic drift and gene flow.
Three evidences of biological evolution, with examples:
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Morphological/comparative anatomical evidence: Organisms that share a common ancestor often show homologous organs — structures with the same basic anatomical plan/origin but adapted to perform different functions, e.g. the forelimbs of a frog, lizard, bird, and human all have the same basic pentadactyl bone arrangement, though modified for walking, flying, or grasping — indicating they evolved from a common ancestral structure (divergent evolution). In contrast, analogous organs such as the wings of a butterfly and a bird have different developmental origins but perform a similar function due to adaptation to a similar environment (convergent evolution) — this too is used to trace evolutionary relationships.
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Palaeontological (fossil) evidence: Fossils are the preserved remains or impressions of organisms from earlier geological ages found in rock strata. Age-wise placement of fossils in different sedimentary layers shows a gradual and connected sequence of change, e.g. Archaeopteryx, a fossil with both reptilian (teeth, long tail) and avian (feathers, wings) features, is considered a connecting link between reptiles and birds; similarly, the fossil series from Eohippus to modern Equus (horse) shows a gradual, traceable increase in body size and change in limb/tooth structure over geological time, providing direct evidence of evolutionary transition.
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Embryological evidence: The comparative study of embryonic development (embryology) across different vertebrate groups shows striking similarities in early developmental stages — for example, fish, chick and human embryos all pass through a stage displaying gill slits/pharyngeal arches, even though only fish embryos develop these into functional gills as adults, indicating a shared evolutionary ancestry among vertebrates.
OR:
(a) Characteristic features of the genetic code:
- Triplet: A group of three nucleotides (a codon) codes for one amino acid.
- Degenerate: Most amino acids are coded by more than one codon (synonymous codons), except methionine (AUG) and tryptophan (UGG).
- Unambiguous and specific: Each codon codes for only one particular amino acid.
- Commaless/non-overlapping: The code is read in a continuous, contiguous fashion from a fixed starting point, without gaps or shared/overlapping nucleotides between codons.
- Nearly universal: The same codon codes for the same amino acid, from bacteria to humans (with a few exceptions in mitochondria and certain organisms).
- Start and stop codons: AUG serves as the initiation (start) codon (also coding for methionine), while UAA, UAG and UGA are stop (termination) codons that do not code for any amino acid.
(b) Dihybrid cross of a pure tall, red-flowered pea plant with a pure dwarf, white-flowered pea plant (Tall 'T' and Red 'R' dominant; dwarf 't' and white 'r' recessive):
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