The Development of Understanding of Genetics & Evolution Flashcards
All 35 cards in this deck
Which two scientists proposed the theory of evolution by natural selection?
Charles Darwin and Alfred Russel Wallace.
What did Darwin base his theory of evolution by natural selection on?
Observations made on a round-the-world expedition, backed by years of experimentation and discussion, and linked to developing knowledge of geology and fossils.
According to Darwin's theory of natural selection, which individuals are more likely to survive to breed successfully?
Those with characteristics most suited to the environment.
Why was there much controversy surrounding Darwin's theory when it was published?
It challenged the idea that God made all the animals and plants that live on Earth.
What did Jean-Baptiste Lamarck's theory of inheritance state?
That changes which occur in an organism during its lifetime can be inherited by its offspring.
True or false? We now know that changes acquired by an organism during its lifetime are passed on to its offspring, as Lamarck suggested.
False. In the vast majority of cases this type of inheritance cannot occur — only genetic changes can be inherited.
What did Alfred Russel Wallace publish with Darwin in 1858, and what did it lead to?
Joint writings on evolution by natural selection, which prompted Darwin to publish On the Origin of Species in 1859.
What work is Alfred Russel Wallace best known for?
His work on warning colouration in animals and his theory of speciation.
What are the steps that give rise to a new species?
e.g. a population of snails split in two by a new river
- The populations become isolated — the snails on each side cannot interbreed.
- Natural selection acts on the variation in each population, selecting different characteristics in each environment.
- The populations become so different that they can no longer interbreed to produce fertile offspring — two species.
How can you tell that two isolated populations have become separate species?
They can no longer interbreed to produce fertile offspring.
True or false? Two isolated populations of the same species experience exactly the same selection pressures.
False. Their environments differ, so natural selection favours different characteristics in each population.
What experiments did Gregor Mendel carry out in the mid-19th century?
Breeding experiments on plants.
What did Mendel conclude about how each characteristic is inherited?
It is determined by 'units' that are passed on to descendants unchanged.
What was observed about chromosomes in the late 19th century?
Their behaviour during cell division.
In the early 20th century, what idea came from seeing that chromosomes and Mendel's 'units' behaved in similar ways?
That the 'units', now called genes, are located on chromosomes.
What major discoveries about inheritance were made in the mid-20th century?
The structure of DNA was determined and the mechanism of gene function was worked out.
True or false? The importance of Mendel's work was recognised straight away by other scientists.
False. Chromosomes and genes had not yet been discovered, so his 'units' could not be explained; his importance was only recognised after his death.
What two types of evidence are used to support the theory of evolution?
Fossils and antibiotic resistance in bacteria.
How does the fossil record provide evidence for evolution?
It shows how organisms have gradually changed over millions of years.
True or false? Antibiotic resistance in bacteria is evidence of evolution happening now.
True. Bacteria reproduce very quickly, so natural selection of resistant strains can be observed over a short time.
Apart from religious objections, give two reasons why Darwin's theory was only gradually accepted.
There was not enough evidence at the time to convince many scientists, and the mechanism of inheritance and variation was not known until 50 years later.
What are fossils?
The 'remains' of organisms from millions of years ago, which are found in rocks.
What are the three ways in which fossils may be formed?
From parts of organisms that have not decayed (one or more conditions for decay absent); when parts are replaced by minerals as they decay; as preserved traces of organisms.
True or false? A footprint preserved in rock counts as a fossil.
True. Preserved traces such as footprints, burrows and rootlet traces are fossils.
Why have many early forms of life left few traces behind?
They were soft-bodied, so they decayed without forming fossils.
Why can scientists not be certain about how life began on Earth?
Early soft-bodied life left few traces, and those traces have mainly been destroyed by geological activity.
Give one reason, other than soft bodies, why the fossil record is less clear for older species.
Older fossils are buried deeper so are harder to find (or are more likely to have been destroyed by geological activity).
What is extinction?
When there are no remaining individuals of a species still alive.
Give three factors that may contribute to the extinction of a species.
New predators, new diseases or new competitors; also catastrophic events, changes to the environment, or destruction of habitat.
True or false? A species is extinct once its numbers have fallen very low, even if a few individuals remain.
False. Extinction means no individuals of that species are still alive.
Why can bacteria evolve rapidly?
They reproduce at a fast rate.
How does an antibiotic-resistant strain of bacteria arise and spread?
e.g. MRSA in a hospital
- A mutation of the bacterial pathogen produces a new strain that is resistant to the antibiotic.
- The antibiotic does not kill it, so it survives and reproduces and the resistant population rises.
- It spreads because people are not immune to it and there is no effective treatment.
Name a bacterium that is resistant to antibiotics.
MRSA.
True or false? Taking antibiotics causes bacteria to mutate and become resistant.
False. Mutations happen randomly; the antibiotic only kills the non-resistant bacteria, leaving resistant ones to reproduce.
Why should patients complete their course of antibiotics?
So that all the bacteria are killed and none survive to mutate and form resistant strains.