Genetic diseases – Mnemonic


Autosomal recessive diseases:

  • SICKLE CELL ANAEMIA: gene present on the 11th chromosome.
  • PHENYLKETONURIA: gene present on the 12th chromosome.
  • THALASSEMIA: α-thalassemia gene is present on 16th chromosome while β-thalassemia gene is present on the 11th chromosome.
  • ALKAPTONURIA: the gene is present on the 3rd chromosome.
  • CYSTIC FIBROSIS: the gene is present on 7th chromosome.

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Loss of Biodiversity


Biological wealth of our planet is declining rapidly. This is due to human activities as they derive benefits from the living world either directly or indirectly. This is due to the diversity of organisms. E.g., Colonisation of Tropical Pacific Island by humans led to the extinction of more than 2000 species of native birds.

IUCN Red List (2004): Extinction of 784 species i.e., 338 vertebrates, 359 Invertebrates, 87 Plants, have occurred in the last 500 years.

Recent extinctions are: 

  • Dodo in Mauritius.
  • Quagga in Africa.
  • Thylacine in Australia.
  • Steller sea cow in Russia.
  • 3 species of Tiger: Bali, Java & Caspian.

In the last 20 years, 27 species have disappeared. Extinction across taxa is not random, some groups like Amphibians are more vulnerable. More than 15,500 species worldwide are facing the threat of extinction.

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Population Interactions – Commensalism and Amensalism


It is an interaction between two species in which one species is benefitted and the other species is neither harmed nor benefitted. The species that benefits is the commensal and the other is the host.

  • Orchids grow as epiphytes on branches of mango.
  • Barnacles growing on whales back. Barnacles are arthropods and their larvae grow on the whale.
  • Cattle ergets and grazing cattle – when the cattle graze the grass it flushes out the insects.The ergets feed on these insects.
  • Clownfish living on the stinging tentacles of sea anemone protects itself from predators.

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Population Interactions – Parasitism


It is a relationship between two organisms in which one organism lives in or on the body of another organism.

The former one is referred as the parasite and the later as host.

Ø   Parasites are usually smaller in size and majority of them are host specific.

Ø   Both host and the parasite tend to co-evolve, i.e., if the host evolves a mechanism for resisting the parasite, the parasite must evolve mechanisms to counteract and neutralize them, to be successful with the specific host.

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Population Interactions – Mutualism


An association between two organisms in which both are mutually benefitted. It is a close physical & an obligatory relationship. Organisms provide resources to each other.

  • Lichens – an association between fungus and algae.
  • Mycorrhizae – an association between fungi and roots of higher plants.
  • Plant-animal relationships – animals help in pollination and seed dispersal.
  • Rhizobium grows in the root nodules of leguminous plants.
  • Coralloid roots in Cycas.
  • Ruminant mammals have microorganisms in their intestine that help in cellulose digestion.

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