5.4 Cladistics

Question 1

What is a clade

Answer 1

This an ancestral species and all of its evolutionary descendant speces that are alive and extinct

members of the clade sharesimilar characteristics due to shared ebolutionary lineage

e.g. all birds form a clade as they have all evolved from one ancestral species

Question 2

how to indentify members of a clade

Answer 2

in the past this has not been easy as it is not clear whihc psecies evolved from which

recent evidence from genetic base sequencing and amino acid sequencinig has mad ehtis easier

if a recent common ancestor - fewer differences in sequence

if a distant common ancestor - more differeneces in sequence

Question 3

what are molecular clocks

Answer 3

mutations cause difference in base sequence of DNA and the seqeunce of amino acids

moutations occur at a constant graudal rate over time so we can use the number of differences beteween the sequences to determine how long ago their common ancestor split and use the mutations as a molecular clock

Question 4

how to analogous and homologous traits complicate it

Answer 4

analogous e.g. human euye and octopus eye are different genetic orgins and superficially similar duie to similar function and covnergent evolutionm

homologous e.g. pentadactly in vertebrate animasl are same genetic orgins but superfically different due to different function - adaptive radiation

this can lead to mistakes in classification especially if morphology (structure and form) are used to classifiy - but now we rely on evidence from base / amino acid sequencing

Question 5

what is cladogram

Answer 5

A cladogram is a tree diagram based on the similarities and differences between the species in a clade - previously morphology

computers are used to determine the exact number of differences in the base/amino acid sequence of all of the species in a clade and then predict how all of these species evolved. These predictions are based on the smallest number of the base/amino acid changes occuring - this known as the principle of parsimony

The branching points are called nodes

Question 6

what are cladistics

Answer 6

Cladistics refers to the identification of clades and the construction of cladograms

Construction of lots of cladograms changed due to the development of base/amino acid sequencing, once we were no longer identifying common ancestors and clades based on just morphology

As a result, lots of cladograms ended up revealing that the likely evolutionary origins of many species was different to what we had previously thought and this led to reclassification of species. E.g reclassification of the figwort family in the Plant kingdom