ZIMSEC O Level Combined Science Notes: Selection

  • Each time male and female individuals reproduce they create an offspring that is different from themselves
  • This changes accrue over time to bring about much change in the descendants as there is inter-breeding between many individuals in each generation
  • This changes might result in the offspring having certain advantageous characteristics that are not present in their contemporary offspring
  • This means the offspring with the advantageous is more likely to survive and thrive compared with the one that does not have that advantage
  • For example during a breeding cycle there are two calves born of different parents
  • One is born with genes that are resistant to diseases and the other is not
  • The one born resistant is more likely to survive and grow up
  • The environment decides or select which offspring will survive
  • This phenomenon is known as natural selection
  • Natural selection-is when the environment decides which offspring will survive usually the strongest members of the given species will survive to breed the next generation
  • Nature selects which offspring will survive to grow and produce the next generation
  • Because the species with the advantageous characteristics survives and breeds the next generation that trait/characteristic is passed on to the next generation
  • For example if there are many calves born and more of those which are resistant to diseases survive and breed the next generation
  • The result is that in each succeeding generation more and more calves are born with those genes
  • With time each generation will be different and should be better suited to the environment in which it lives
  • The weaker members who lack the advantage die off and less of them breed
  • Natural selection has been happening for millions of years
  • It is a slow process
  • Humans can influence the selection process to their advantage
  • For example farmers can choose and plant the breeds they want to produce based on their needs
  • Scientists breed crops that grow best in the local conditions for example drought resistant crops breeds and crop breeds that mature more quickly
  • This is known as artificial selection
  • Artificial selection-this is when humans influence the selection process to their advantage for example hybrid breeding of crops
  • Typically the male and female individuals are carefully selected and mated
  • Agriculture benefits greatly from artificial selection
  • Breeds of cattle, sheep and goats that are suited to local conditions are bred
  • Important features such as improved milk and meat yields, increased drought tolerance and increased resistance to diseases are fostered in the breeding process

To access more topics go to the Combined Science Notes page.

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