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Species• Species: group of organisms that can
interbreed and produce fertile offspring– Different species rarely breed– Interspecies breeding often
results in sterile offspring• Ex: Horse x Donkey = Mule• Ex: Lion x Tiger = Liger
• Acquired Inheritance: Early theory where organisms could acquire and pass traits after birth
• Cause: environmental changes forced individuals to change• Early Belief: Giraffes & Long Necks– Long necks are result of stretching to reach leaves– Extra length was passed on to offspring
• Problem: Traits acquired after fertilization cannot be passed to offspring
PROVEN WRONG!
Geologic Change• Early belief:– Earth ~6,000 years old– Life remained unchanged
• “New” Observations– Rock layers (strata) contained
differing fossils– Deeper fossils (older) less
complex– Environmental changes
thought to affect life characteristics
Charles Darwin
• Observed:– Organisms have variations based upon environment– Similarities between extinct fossils & modern life– Marine fossils atop mountains
• Natural Selection: Process where organisms with favorable traits survive and reproduce
• Major concept in biology published in The Origin of Species (1859)
Adaptation & Variation
• Variation: Inherited traits that make an individual different from others– Green, flat wings of the insect above
• Adaptation: Variation increases the chance of survival– Ability to blend with environment
Causes of Genetic Variation
• Genetic variation increases chances some survive in changing environments
• Gene Pool: All alleles within a population• Two main causes of genetic variation:
1) Mutations: Random genetic changes may affect phenotypes2) Recombination(crossing over): During meiosis, genes recombine in varying
patterns
Variation: 4 Different Gametes
Chromatids
copied
Chromatids
copied Crossing-
over
Crossing-
over Crossing-
Over
finished
Crossing-
Over
finished
Genetic variation!
Four differing chromatids
Genetic variation!
Four differing chromatids
1) When are two organisms considered a different species?2) Even though incorrect, why is Lamarck’s theory still relevant?3) How can the general age of rocks (and fossils) be determined?4) How does a variation and adaptation differ?5) What is natural selection?
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