A4 Flashcards
Biological evolution
Change in the heritable characteristics of a population. Heritable traits are rooted in DNA, refers to populations, not individuals or species.
Why is Lamark’s theory falsified?
Lamark’s theory- we adapt to our environment over our lifetime and get characteristics which are passed on. e.g giraffe’s neck stretches over its life due to use, and then this is passed on. We now know that offspring inherit DNA which cannot be altered over a lifetime- changes over lifetime cannot be passed on.
What is Darwin’s theory of natural selection?
- Alterations in heritable material give rise to different traits in a population
- Some of these aid in survival, organisms that survive longer are able to reproduce, thus more offspring are born each generation with the trait
What is falsification?
- Falsification: when there is evidence that determines a theory to not be true
- It is hard for scientific theories to be proven to be true, so we instead seek lack of falsification
What are the forms of molecular evidence for evolution
- DNA
- RNA
- Proteins
What are Hox genes?
Hox genes are a gene family (group of related genes) that play a role in determining body plans of organisms during development.
How do Hox genes relate to evolution
If there is similarity in Hox genes across very different organisms, there could be common ancestors between them.
What is a phylogenetic tree and what does it show?
- Phylogenetic trees are visual diagrams that show which organisms are most similar or related
- Organisms on closer branches have more genetic similarity
note: can be used for a whole genome or just a single common gene
What is our current understanding of evolution?
differences to Darwin’s theory
The heritable material is DNA- which does not change during an organisms lifetime
What are the steps involved in the process of natural selection?
in brackets= what we know now but darwin didn’t
- Differences exist in heritable material (changes in DNA due to mutation)
- (Genetic) variation in a population
- There is a survival pressure- threat to survival e.g abiotic factors, competition for resources, predators and disease
- In that environment some variations (adaptations) increase likelihood of survival
- Those with the desirable adaptation produce more offspring- SURVIVAL OF THE FITTEST
- Adaptation is passed onto their many offspring
- Increased frequency of the adaptation within population change in heritable trait= evolution!
DNA as a form of evidence for evolution
how and strengths/ weaknesses
How: comparison of the base sequences
Strengths:
- provides more information, including all differences detected and silent mutations
- This makes it good for closely related species
Weaknesses:
- Difficult to isolate and sequence DNA (but getting easier)
- Can be overly complex
RNA as a form of evidence for evolution
how and strengths/ weaknesses
How: comparison of the base sequences (same idea as DNA)
Strengths:
- Useful for viral evolution- viruses only have RNA
Weaknesses:
- Equally as difficult to sequence as DNA
- Harder to isolate than DNA
Proteins as a form of evidence for evolution
how and strengths/ weaknesses
How: comparison of amino acid sequences of a shared protein
Strengths:
- Much easier to sequence and obtain as it is an older technology
Weaknesses:
- It shows less differences and data- can be good as it is more simple
Selective breeding
Breeders choosing the males and females with the most desirable characteristics for agriculture and breed them together
Artificial selection
Is a result of selective breeding. Generations of selective breeding causes new traits aka evolution- but not natural
Homologous structures
Similar internal structures between organisms but can be used for different purposes. Suggests a common ancestory but over time have changed to suit specific functions. Evidence of divergent evolution
Pentadactyl limbs
Presence of 5 digits- fingers or toes- generally front or hind limb. Made up of the same set of bones across organisms- homologous structures
Analagous structures
Body parts that carry out similar functions but have different structures. Suggests a lack of common ancestry. Evidence of convergent evolution.
Convergent evolution definition
Species that develop similar adaptatioms on their own independent evolutionary journeys, but exist in similar environments, so have similar adaptations.
Examples of organisms that have undergone significant selective breeding
- Modern corn- selected for larger kernals and protective leaves
- Modern dogs- originate from grey wolf
- Cannabis- bred for high THC content, average THC has quadrupled in 23 years
Functional variations of pentadactyl limbs in animals
- Walking on the limb (most animals)
- Use as a hand (bipedal humans)
- Use as a fin (aquatic mammals e.g whales and dolphins)
- Use as a wing (bats)
Similarities and differences between artificial and natural selection
similarity acts as evidence of natural selection
Similarities:
- Both start with genetic variation
- Both end with one variation having more offspring causing it to increase in frequency
Differences:
- Natural selection results from pressures in the environment which determines who survives
- Selective breeding results from humans prefering some individuals and mating them more
Speciation
Formation of new species by the splitting of an existing species- population that could previously interbreed can’t now, therefore are different species
Reproductive isolation
2 populations that are unable to successfully interbreed, therefore preventing gene flow between groups. Could be due to geographical barriers, anatomical incapability or misalignment of mating behaviours.
Geographic isolation
Physical barrier that makes it impossible for males and females to come into contact, therefore mating is never able to be attempted. e.g mountain range, water