CHAPTER 9: RELATEDNESS OVER TIME Flashcards
1
Q
what does related mean
A
species that are more closely related are those that have most recently shared a common ancestor
2
Q
determining relatedness
A
- biogeographic distribution
- comparative
- anatomy - structural morphology
- embryology - developmental biology
- molecular homology - DNA and amino acid sequences
4
Q
structural morphology - homologous structures
A
- homologous structures are those structures that have been derived from a common ancestor
- would show similarities in structure
- even though they may have different functions
- morphological changes can be achieved through mutations that change the time or the place (when and where) genes are active
- evolution commonly occurs by modification of pre-existing structures - not by the production of TOTALLY new structures
- eg. mammalian forelimbs
- each of these mammalian limbs has a similar number of bones arranged in the same basic patter
- even though the limbs may serve different functions
5
Q
structural morphology - vestigial structure
A
- vestigial structures are structures that are non-functional remnants of structures that were functional in ancestral species
- eg. whale
- skeletons show the presence of a reduced pelvis and in some cases, vestiges of bones of the hind limbs
- EG. HUMANS
- muscles are evidence that our ancestors were once able to move their ears - a trait that assists other mammals in locating direction of sound
- hair is sparsely spread over majority of the body - goosebumps no longer perform this function
6
Q
what is molecular homology
A
involves comparing the similarities in DNA and protein sequences to infer relatedness
7
Q
amino acids for molecular homology
A
- proteins from different species can be compared in terms of their amino acid sequences
- species that are more closely related are expected to have fewer differences in the amino acid sequences of their corresponding proteins than species that are more distantly related
8
Q
orthologous proteins
A
- orthologous proteins are derived from a common/shared ancestor in which the primary function is conserved
- can determine relatedness between species
8
Q
what is structural morphology
A
- the process of comparing similarities in body structures to infer relatedness
- fossil record
9
Q
comparing amino acid sequences in haemoglobin
molecular homology
A
- amino acid sequences in haemoglobin chains have been identified for many animals
- the more closely related species are the more similar the amino acid sequences of shared proteins will be
- less time has passed for changes to occur
10
Q
challenges with amino acid sequencing
A
- multiple triplets can code for a particular amino acid
- genetic code is redundant
- some mutations (silent mutations) aren’t visible in amino acid sequencing
- also sometimes two mutations that occur in the same codon will only cause one amino acid change.
11
Q
comparing DNA base sequences
molecular homology
A
- species that are closely related by evolutionary descent will show more similarities in the base sequences of their common genes
- this in turn can be used to produce phylogenetic trees
12
Q
comparing whole genomes
A
- comparisons of genomes of different organisms can help clarify the evolutionary history of species
- living species have evolved from common ancestors → the genomes of related species exhibit similarities
- the more recent the divergence of two related species from a common ancestor the greater the number of conserved DNA sequences and of their ARRANGEMENT within the genome
- reveals genes that are conserved in different species
- make inferences about the phylogeny and evolutionary history of a species
13
Q
why molecular homology can measure relatedness
A
- mutations accumulate in DNA over time
- if 2 species share a common ancestor recently - there will be fewer mutations as less time has passed for these to have occurred
- if 2 species shared a less recent ancestor
- more time has passed → the more likely mutations are going to occur
- species are related through evolution with the degree of relatedness differing according to when the two species last shared a common ancestor
- fewer differences in DNA and amino acids sequences between species suggest a closer degree of relatedness between them
14
Q
which is more accurate for determining relatedness
structural morphology or molecular homology
A
- molecular homology can show two species are closely related even if their structural morphology is very different
- molecular homology provide stronger support than structural morphology alone
- two species may have similar features that evolved independently (through analogous evolution), so using structural features alone may incorrectly suggest relationships.
15
Q
features of a phylogenetic tree
A
- tips represent species or group
- nodes show common ancestors
- line lengths indicates time
- branch indicates speciation event
- root - common ancestor of all the descendant groups in the tree
- sister taxa - two groups like two species with a common ancestor that are not shared with other groups
