191 DNA Differences Between Species
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with more differences. Often one gene is used to make the comparison. It is good practice to choose a gene that is large enough to show difference between species, but is still small enough so that any differences can be easily compared. The sequences below are for a gene called cytochrome oxidase I (COXI). It is involved in cell respiration.
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PR E O V N IE LY W
Key Idea: The sequence variations between species can give information about their relationships. These sequence variations can be visualised on an electrophoresis gel. Comparing the DNA sequences of several species can provide information about their relatedness. Species with fewer differences are more closely related than species
T A G T
T
A
G
C
T
Cow
A
G
C
Sheep
T
A
G
C
Goat
T
A
G
C
Horse
1. For each of the species above:
(a) Determine the sequence of synthesised DNA in the gel in the photographs above. The synthesised DNA is what is visible on the gel. Cow: synthesised DNA: Sheep: synthesised DNA: Goat: synthesised DNA:
Horse: synthesised DNA: Based on the number of differences in the DNA sequences:
(b) Identify the two species that are most closely related:
(c) Identify the two species that are the least closely related:
WEB
KNOW
A
B
C
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D
E
CL
Calibration
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2. Determine the relatedness of each individual (A-E) using each banding pattern on DNA profiles (below). When you have done this, complete the phylogenetic tree by adding the letter of each individual.
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