General Biology (2ND SEM) Part II Flashcards
is a powerful and important process. It is a process which, over billions of years, gradually selects the organisms that are better adapted to their environment to continuously change life and make all living organisms in our world the way they are today.
Biological evolution
is not a finished event wherein humans are the final product.
Evolution
Rather, it is a continuing process which has been changing and forming life on Earth for billions of years, and continues to do so for as long as organisms are born, dying and competing for what they need to survive and reproduce.
Evolution
“Species are groups of interbreeding natural populations that are reproductively isolated from other such groups.”
Species - Ernst Mayer’s definition
The ___________________ are a collection of evolutionary mechanisms, behaviors and physiological processes critical for speciation. They prevent members of different species from producing offspring, or ensure that any offspring are sterile. These barriers maintain the integrity of a species by reducing gene flow between related species.
Reproductive Isolating Mechanism
- prevents fertilization and zygote formation
Pre-zygotic isolation mechanisms
- happens before fertilization occurs between gametes
Pre-zygotic isolation mechanisms
5 Pre- Zygotic Isolation Mechanisms
Geographic or Ecological or Habitat Isolation
Temporal or Seasonal Isolation
Behavioral Isolation
Mechanical Isolation
Gametic Isolation
- occurs when two species that could interbreed do not because the species live in different areas. The two species live in different habitats and will not encounter one another: each is isolated from the other species.
Geographic or ecological or habitat isolation
- different groups may not be reproductively mature. For example, two populations of plants may produce flowers in different seasons, making mating between the populations impossible.
Temporal or seasonal isolation
- patterns of courtship is different.
Behavioral isolation
- differences in reproductive organs prevent successful interbreeding.
Mechanical isolation
- incompatibilities between egg and sperm prevent fertilization. Often this occurs because the female immune system recognizes sperm as foreign and attacks it.
Gametic isolation
3 Post- Zygotic Isolation Mechanisms
Hybrid Inviability
Hybrid Sterility
Hybrid Breakdown
- fertilized egg fails to develop past the early embryonic stages.
Hybrid Inviability
- their hybrids are sterile because gonads develop abnormally or there is abnormal segregation of chromosomes during meiosis.
Hybrid Sterility
- F1 hybrids are normal, vigorous and viable, but F2 contains many weak or sterile individuals
Hybrid Breakdown
