Taxonomy - Lecture notes 3-6 PDF

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Taxonomy The science of Taxonomy seeks to provide a mechanism for dividing organisms into groups or Taxa (singular Taxon). The smallest natural Taxon is generally considered to be the Species Taxonomy is essentially the science of Identification and forms the basis for all biological work and is necessary because of the immense diversity of living forms. No comparative work can be undertaken until organisms are identified. Identification Involves the use of Taxonomic Characters and Character States A character could be for example: A character state:

presence of teeth number of teeth

A wide variety of Characters (and hence character states) is available for identification and they may be: Morphological

Macroscopic Microscopic

Biochemical

Structural Physiological Immunological

Genetic

DNA RNAs Proteins Traits

Ecological

Habitat Geography

Behavioural

Characters may be divided into two distinct types Meristic Morphometric

Vary discontinuously Vary continuously

In practice Identification of Taxa is usually in the form of Dichotomous Keys, based of course on characters and character states which can be used to identify species or in the following example, wild type from mutant fruit flies, Drosophila melanogaster.

The Character used to identify and separate the Wild Type from the mutant would be the presence of Red Eyes (the mutant having White eyes). The Character used to separate male from female would be the presence of a Sex Comb in the male, but not in the female. When organisms are collected from their natural habitat, they need to be separated into major taxonomic groups prior to identification to species level. Organisms in different taxa can be quantified by counting or using abundance scales. This practical involves the use of keys and measuring morphometric characteristics of Drosophila.

Introduction The fruit fly Drosophila melanogaster is an organism which has been widely used in laboratories for basic work on the study of genetics. The advantage of this organism is that it is small, easily kept in the laboratory and has a short life cycle (hence may generations can be examined in a relatively short period of time) Another advantage of Drosophila is that it is easy to breed and therefore it is possible to study a wide variety of genetic crosses. Coupled to this is the fact that this species is highly mutable and has therefore been valuable in assessing mutation rates and in studying the factors involved in the production of mutations.

Drosophila is a typical winged insect and therefore the general features of its morphology are well known and easy to recognise. The aims of the practical are: 1. To examine the usefulness of different characters in identifying male and female Drosophila. 2. To produce a dichotomous key to identify 9 insects.

Materials and Methods To examine the value of meristic and morphometric characters in separating the sexes in all types of Drosophila (see Table 1 and Figures 1,2 and 3).

Table 1: Characters/character states used to separate the sexes in Drosophila Male Smaller Rounded Abdomen Abdomen darker with heavy bristles Presence of Sex comb on anterior leg (see figs 1, 2 & 3)

Female Larger Pointed Abdomen Abdomen lighter few bristles Sex comb absent

Figure 1: Illustrating the sex comb on the first tarsal segment on the anterior leg of a male Wild type(red eye) Drosophila. The sex comb (a dark band) is present in males of all types of Drosophila

Figure 2: High power image of sex comb on the first tarsal segment on anterior leg of male Drosophila

Figure 3: Illustrating morphometric and meristic characters in male (to the left) and female (to the right of figure).

Dichotomous Key You are provided with a diagram (Figure 4, see below) which shows a number of organisms, which are insects, A-J. Construct a dichotomous key which will separate and identify these organisms. Indicate clearly the characters and character states you have used to erect your key (see figure 4 below). FOR HELP WITH CONSTRUCTING THE KEY PLEASE READ THROUGH THE next 2 FOLDERS in the Week 29-31 area.

Results Comment on characters you used to separate the sexes in Drosophila Display a dichotomous key which will separate and identify these insects. Indicate clearly the characters and character states you have used to erect your key (see figure 4 below).

Discussion Compare your results used for sexing of Drosophila and discuss which character or character states were used to separate the male and females. Comment on the value of the characters you used to separate the sexes in Drosophila. What are the applications of dichotomous keys? THE INFORMATION GATHERED IS TO HELP YOU WITH THE SUMMATIVE ASSESSMENT AND THE LAB EXERCISES.

In the practicals, in weeks 29-31, you will observe specimens of wild type and white eye Drosophila. Please complete the summative assessment when you have competed all 3 parts of the week 29-31 material. You have multiple attempts at the summative assessment.

Figure 4 : 9 insects to use to construct a dichotomous key....