Species and Taxonomy

Question 1

Define species.

Answer 1

A group of organisms that share certain observable characteristics and are able to reproduce to give fertile offspring.

Question 2

How can species differ? (Example)

Answer 2

• the diploid number of chromosomes in their cells.

If haploid gametes from two different species undergo fertilisation, the cell that forms has a different number of chromosomes to each parent.

A horse gamete has 32 gametes whereas a donkey gamete has 31. So the cells of a mule (a hybrid of the 2) have 63. Cells with an odd number of chromosomes cannot carry out meiosis because an odd number of chromosomes cannot form homologous pairs. This means mules cannot reproduce and are sterile.

Question 3

What is the phylogenetic classification system?

Answer 3

A system of classification based on evolutionary origins and relationships.

Question 4

Define hierarchy.

Answer 4

The placing of smaller groups within larger groups and with no overlap between them.

Question 5

Define taxa.

Answer 5

Series of groups.

Question 6

What is the highest ranked taxon?

Answer 6

Domain.

Question 7

All living organisms are place in one of the three domains. What are they?

Answer 7

the Bacteria, the Archaea and the Eukarya.

Question 8

What do the three living domains reflect?

Answer 8

Fundamental difference in the RNA sequences found in the organisms within the taxa (the three groups).

Question 9

Classification system?

Answer 9

Domain |
Kingdom |
Phylum |
Class |
Order |
Family |
Genus |
Species |

Question 10

In which category of the classification system is there the greatest number of species?

Answer 10

Domain (there’s only three domains in which all living organisms are place into)

Question 11

In which category of the classification system is there the most similarity between organisms?

Answer 11

Species (compared to domain at the other end where there’s only three domains in which All living organisms are placed).

Question 12

The physical features that help to classify an organism are mainly determined by…

Answer 12

Its genes.

Question 13

What’s a gene?

Answer 13

A piece of DNA that codes for a protein.

Question 14

What happens if a mutation occurs in a body cell?

Answer 14

The mutation occurs only in the individual.

Question 15

What happens if a mutation occurs in sex cells?

Answer 15

The next generation inherits the change.

Question 16

What happens when a mutation is passed through generations through sex cells?

Answer 16

The mutation may make no difference to the characteristics we see in a species, or they can cause the species to change very slowly over a period of many thousands of years.

Question 17

What’s the difference between DNA now and DNA in past ancestors?

Answer 17

The DNA that codes for a particular protein in an organism alive today is slightly different from the DNA that codes for the same protein in its different ancestor.

Question 18

How can we use computer software to compare DNA (or mRNA) base sequence in different organisms?

Answer 18

If the sequences are very similar, it suggests that the organisms concerned are very closely related and that they originated from a common ancestor relatively recently.

If there are are more differences between the sequences, it suggests that the organisms are not so closely released and probably originated from a common ancestor a longer time ago.

Question 19

Why can we use mRNA to compare base sequences to tell different organisms?

Answer 19

Because as mRNA is derived from the base sequence of DNA, sequencing mRNA gives the base sequence of DNA. Plus mRNA is sometimes easier than DNA to isolate from the cells of organisms.

Question 20

Using the DNA simple scoring system, what does a high score show?

Answer 20

The those two species are most closely related as they have the highest number of matching bass.

Question 21

Why can we compare amino acid sequences to decide which species an organism is in?

Answer 21

Because the amino acid sequence reflects the base sequence on the DNA, but proteins are sometimes easier to isolate from the cells of organisms than DNA is.

Question 22

A table shows that both chains in chimpanzee haemoglobin have exactly the same sequences of amino acid as both chains in human haemoglobin. Does this mean they are the same species?

Answer 22

No. Because this data is only for one molecule (haemoglobin). They could be the same because it takes a very long time for differences in the amino acid sequence of haemoglobin to evolve.

And the few million years that have passed since humans and chimpanzees split apart from a common ancestor may be too short of a time for differences in their haemoglobin to have the evolved.

Question 23

Explain why it is often easier to obtain mRNA sequence data from tissue samples (rather than DNA)?

Answer 23

Because mRNA molecules can be found in the cytoplasm of cells, and there are often many molecules of the same mRNA present because of repeated transcription.
Isolating these us often easier than finding a gene in the DNA zinc the nucleus.