Unit 4 - Variation and Evolution Flashcards
Give 4 sources of evidence for evolution
- Palaeontology (fossils)
- comparative anatomy
- comparative biochemistry
- comparative embryology
How can the relative age of fossils be determined?
- over time sediment is deposited to form rock strata
- recent rock strata are found at the top and older rock strata are found at the bottom
- radioisotope dating can be completed on fossils to date rock strata
How do fossils provide evidence for evolution?
- fossils of the simplest organisms are found in the oldest rocks
- fossils of more complex organisms are found in more recent rocks
- allow relationships between extinct and living organisms to be investigated
- sequence in which organisms are found matches ecological links
What is comparative anatomy?
The study of similarities and differences between different organisms’ anatomy
How does comparative anatomy provide evidence for evolution?
-Homologous structures provide evidence for divergent evolution and that from a common ancestor different species have evolved
What are homologous structures?
A structure which appears superficially different (and may perform different functions) in different organisms but has the same underlying structure
What is divergent evolution?
Species diverge over time into two different species, resulting in new species becoming less like the old one
What is comparative biochemistry?
Similarities and differences between the chemical make up of organisms
How does comparative biochemistry provide evidence for evolution?
- molecules change over time
- some important molecules are highly conserved among species
- slight changes that do occur in these molecules can help identify evolutionary links
How does comparative embryology provide evidence for evolution?
- embryos of different animals looks very similar
- shows animals develop in a similar way
- implies the process of embryonic development has a common origin
What is variation?
Differences in characteristics or genes within or between species
Define intraspecific variation
Differences between individuals within the same species
Define interspecific variation
Differences between different species
What are the 2 causes of variation?
Environment and genetics
Are environmental effects heritable?
No
Give 2 examples of environmental effects
Hair dye
Diet
Are genetic factors heritable?
Yes
What are the 5 causes of genetic variation?
- presence of a different allele
- random fertilisation/random fusion of gametes
- random mating
- meiosis
- mutations
What are the two types of mutations?
Point mutations and chromosomal mutations
What are point mutations?
Change in the base sequence of DNA
How do chromosomal mutations arise?
From crossing over
What are the two sources of variation in meiosis?
- crossing over
- independent assortment
What are the two types of variation?
Continuous and discontinuous
What is continuous variation?
- Variation of all possible intermediate values between the two extremes
- it can be plotted to give a normal distribution curve
Give 2 examples of continuous variation
Height
Weight
What is discontinuous variation?
- discrete groupings of individuals
- presented as a bar chart
Give an example of discontinuous variation
Blood group