B15: Genetics and evolution Flashcards
Describe Darwin’s research?
In the 1800s, he took part in an expedition around the world and collected a vast number of different animals and plants. He was fascinated by the huge variety of living organisms that he saw and began to wonder how all of this variety developed. He spent many years studying geology and fossils, these showed that many species of animals and plants alive today are similar to extinct species. After many years of discussion, he began to develop his theory of evolution by natural selection.
Uh, species?
Within a species, we can see a wide range of genetic variation for any characteristic.
Individuals with characteristics most suited to the environment are more likely to survive and breed successfully. e.g. giraffes with longer necks can reach leaves on top of trees.
The characteristics that have enabled these individuals to survive are passed on to the next generation.
Why was Darwin’s theory only gradually accepted?
At the time, many people believed that God made all of the animals and plants that lived on Earth, and Darwin’s theory challenged that.
Many scientists felt that Darwin did not have enough evidence to back up his theory.
People did not understand how characteristics are inherited - genetics was not understood until 50 years after Darwin’s theory was published.
What was Lamarck’s theory
He suggested that when a characteristic is regularly used, it becomes more developed - this strengthened characteristic is passed onto the offspring.
What is the problem with Lamarck’s theory?
In the majority of cases, changed that occur in an organism’s lifetime, cannot be passed onto offspring, therefore his theory is incorrect.
Who was Alfred Russel Wallace?
He was investigating warning colouration in animals an wanted to know how it evolved. As a result of his studies, he independently proposed the theory of evolution by natural selection. Darwin and Wallace realised that they both proposed the same theory, so in 1858 they both jointly published their findings.
What is speciation?
How new species are made.
Wallace noticed that closely related species were often separated by geographical barriers, such as a wide river. Since then, more evidence has led to our current understanding of speciation.
How do new species form?
e.g. snails.
In a population, snails of the same species can interbreed, and if there is a mutation, it will spread through the whole population. There will only be the same species of snail in that area. However, if a geographical barrier is introduced, such as a river, then the snails on one side of the river would not be able to reproduce with the snails on the other side of the river, and this can result in mutations from one side not being passed down to the other. Eventually the snails develop extremely different phenotypes, to the point where they can no longer interbreed, and 2 new species have been made.
What conditions must be there for speciation to take place?
A geographical barrier is needed to separate the population into 2 and prevent interbreeding between the 2 populations.
Who was Gregor Mendel?
In the mid 1800s, he carried out thousands of breeding experiments on pea plants. At the time, scientists didn’t understand how inheritance worked - many believed that characteristics were blended when they were inherited. Mendel looked at the characteristics of pea plants e.g. colour of flowers or shape of the pod. He realised that characteristics are not blended e.g. shape of pea pod has no effect on the colour of the flowers. He said that characteristics are determined by inherited units (genes) which do not change when passed onto descendants. He also showed that some characteristics could be masked, and reappear in later generations (recessive alleles)
What happened in the late 1800s?
Scientists looked at how chromosomes behave during cell division. Around the same time, Mendel’s work was rediscovered, and by the early 1900s, the realised that Mendel’s units behaved in a similar way to chromosomes. They renamed units to genes and realised that genes must be located on chromosomes. In the mid 1900s, scientists determined the structure of DNA and how genes function.
Why can species become extinct?
Catastrophic event e.g. asteroids
Environment changes e.g. changing weather patterns
New disease/ new predator kills all of the individuals of a species and make it extinct.
A new, more successful species evolves and competes with it.
What is a fossil?
The remains of organisms from millions of years ago which are found in rocks
How do fossils form?
- Can form when parts of organisms have not decayed - can happen when the conditions needed for decay are absent e.g. if temp it too cold or there is not enough oxygen or not enough water.
- Form if parts of the organism are slowly replaced by minerals during the decay process.
- Can be preserved traces of organisms e.g. footprints or burrows, and plants can be preserved spaces where roots were.
What is the problem with fossils?
Many of the earliest forms of life were soft-bodied organisms (no shell or skeleton). They very rarely form fossils, and many fossils that did form have been destroyed by changes to rocks in the Earth’s crust.
There are so few fossils of the early forms of life, so scientists can’t be certain about how life on Earth began.
