Natural Selection and Genetic Modification Flashcards
(33 cards)
What is natural selection?
Individuals in a population show genetic variation because of differences in alleles from mutations. Predation, competition for resources and disease act as selection pressures. Individuals with beneficial characteristics have a better chance of survival so are more likely to breed. This means the alleles are more likely to be passed on, while worse alleles are less likely to survive. Beneficial characteristics become more common over time.
How do bacteria provide evidence for evolution?
Bacteria sometimes develop random mutations in their DNA, creating new alleles and characteristics. The characteristic could be better resistance to antibiotics. This is a big advantage for bacteria, as it is more likely to survive, so it lives longer and reproduces many more times. This leads to antibiotic resistance being passed on to lots of offspring, so it spreads.
How did Darwin come up with the theory of evolution by natural selection?
He spent 5 years on a voyage around the world studying plants and animals on a ship called HMS Beagle. He noticed variation in members of the same species and that characteristics most suited to the environment were more likely to survive. He also noticed that characteristics could be passed on to offspring. He wrote his theory to explain his observations.
How did Wallace contribute to the theory of evolution?
He was a scientist working at the same time as Darwin. He independently came up with the idea of natural selection and they published their papers together, acknowledging each other’s work. He provided lots of evidence, such as warning colours used by some species to deter predators, an example of a beneficial characteristic that had evolved.
How do fossils give us clues about human ancestors?
Evidence from fossils suggests that humans and chimpanzees evolved from a common ancestor that existed about 6 million years ago. Human beings and ancestors are known as hominids, with several species found. They have characteristics between apes and humans, allowing us to see how humans have evolved over time.
Who is Ardi?
She is a fossil of the species Ardipithecus ramidus, found in Ethiopia and 4.4 million years old. Her feet structure suggests she climbed trees, with an ape like big toe. She had long arms and short legs, with a brain size about the same as a chimpanzee’s. she probably walked upright without using her hands for help.
Who is Lucy?
She is a fossil of the species Australopithecus afarensis, found in Ethiopia and 3.2 million years old. She had arched feet and no ape like big toe, better adapted to walking. The size of her arms and legs was between apes and humans. Her brain was slightly larger and she walked upright more efficiently.
What fossils did Leakey find?
Richard Leakey and his team organised an expedition to Kenya. One of their finds was Turkana Boy, a 1.6 million year old fossil skeleton of the species Homo erectus. He is more human like than Lucy, with short arms and long legs, and a much larger brain similar to human size. He was even better adapted to walking upright than Lucy.
How does the development of stone tools provide evidence for human evolution?
From 2.5-1.5 million years ago Homo habilis made simple stone tools called pebble tools by hitting rocks together to make sharp flakes.
From 2-0.3 million years ago Homo erectus sculpted rocks into shapes to produce more complex tools like simple hand axes.
From 300,000-25,000 years ago Homo neanderthalis made more complex tools out of materials like flint.
From 200,000-present Homo sapiens used flint and pointed tools, more recently making hooks, buttons and needles.
How can stone tools be dated?
Looking at structural features - simpler tools are likely to be older
Using stratigraphy - the study of rock layers. Older rock layers are normally found below younger layers
Using carbon-14 dating - tools found with carbon-containing material e.g. wood can be dated accurately
How does the pentadactyl limb provide evidence for evolution?
A pentadactyl limb is a limb with five digits. It is found in many species of mammals, reptiles, amphibians and others. They all have a similar bone structure but different functions. This suggests all these species came from a common ancestor but evolved in different ways.
How were organisms classified in the past and today?
Traditionally they were classified according to similarities and differences in their observable characteristics. Microscopes were then used to identify smaller characteristics e.g. cell structure. We can now determine the sequence of DNA bases in different organisms’ genes and compare them, and the same with RNA.
What is the five kingdom classification system?
Organisms are divided into five kingdoms: animals, plants, fungi, prokaryotes, and protists. The system goes:
Kingdom, Phylum, Class, Order, Family, Genus, Species
King Phillip Came Over For Good Soup
What is the domain system for classification?
Using RNA sequencing, Woese found that some members of the Prokaryote kingdom were not as closely related as first thought. He split this kingdom into Archaea and Bacteria. He created the domain classification first:
Archaea - look similar to bacteria but are different, first found in extreme places
Bacteria - true bacteria
Eukarya - fungi, plants, animals, and protists
What is selective breeding?
When humans artificially select the plants or animals that are going to breed so that the genes for particular characteristics remain in the population. Organisms are selectively bred to develop features that are useful or attractive.
What are some examples of selective breeding?
Animals that produce more meat or milk
Crops with disease resistance
Dogs with a good, gentle temperament
Plants that produce bigger fruit
How does selective breeding work?
Select from your existing stock ones with the characteristics you want
Breed them with each other
Select the best of the offspring and breed them together
Continue this process over several generations and the desirable trait gets stronger and stronger
What are the disadvantages of selective breeding?
It reduces the gene pool - the number of different alleles in a population. The ‘best’ animals used for breeding are closely related, so inbreeding occurs.
Inbreeding can cause health problems because there is more chance of inheriting harmful genetic defects. This leads to ethical considerations, particularly if negative characteristics are bred for research.
Less variation means there is less chance of resistance alleles being present for new diseases, so disease can wipe out lots of the population.
What is tissue culture?
The growing of cells in an artificial growth medium
What are the advantages of tissue culture in plants?
Whole plants can be grown via tissue culture. This is very easy, can happen very quickly, in very little space, and all year round. Plants produced are clones. This means you can replicate the same beneficial features, such as pesticide resistance or tasty fruit.
How is tissue culture in plants carried out?
Choose a plant you want cloned and remove a small piece of tissue, ideally from fast growing root or shoot tips
Grow the tissue in a growth medium containing nutrients and growth hormones. This is done under aseptic (sterile) conditions to prevent growth of microbes
As the tissues produce shoots and roots they can be moved to potting compost to carry on growing
What are the advantages of tissue culture in medical research?
You can carry out experiments in isolation, looking at the effects of a particular substance or environmental change on the cells of a single tissue, without complications from other processes in the whole organism.
You can use just a small layer of tissue, allowing you to see processes directly
How is tissue culture in animals carried out?
A sample of the tissue you want to study is extracted from the animal
The cells in the sample are separated from each other using enzymes
They are placed in a culture vessel and bathed in a growth medium containing nutrients, allowing them to grow and multiply
After several rounds of cell division, the cells can be split up again and placed into separate vessels for further growth
Once the tissue culture has been grown, it can be stored for further use
What are restriction enzymes?
Enzymes that recognise specific sequences of DNA and cut the DNA at these points, leaving them with sticky ends
