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3.02 – Dichotomous Keys
Biology 11
Keying….
To determine the scientific name of an
organism, taxonomists use a process of
elimination called keying to assist them
y Each
ac step in tthee identification
e t cat o process
p ocess
involves the selection of a characteristics
from each pair
y
Dichotomous Key
Keys consist of a series of choices that
lead the user to the correct name of a
given item.
y "Dichotomous"
c oto ous means
ea s "divided
v e into
to two
parts".
y Therefore, dichotomous keys always give
two choices in each step.
y
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1a Wings covered by an exoskeleton – go to step 2
1b Wings freely observed – Go to step 3
2a Body has a round shape ……….ladybug, a red beetle
p
with black spots
2b body has an elongated shape ……….grasshopper, a
green insect that hops
3a wings point out from the side of the body…...dragonfly,
an insect that is 10- 15 cm long and lives in marshes
3b. wings point to the posterior of the body……….housefly,
a flying insect with red eyes and an annoying buzz
When Making one….
Look over the group of organisms that
you are trying to key
y Choose a characteristic that allows you
to divide
v e tthee ggroup
oup into
to 2 parts
pa ts
y Continue sub dividing the groups into 2
parts based on other characteristics
y Number the steps starting with 1A and
1B, then 2A and 2B, etc.
y
Spider Keys…
y
Are used to help organize the information
and then you can write the dichotomous
key
y
It also provides a more graphical method
of representing a dichotomous key.
2
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Spider Key
Dichotomous Key
3