Defining species

Question 1

Define population.

Answer 1

When a group of individuals belonging to the same species occupy the same space and interbreed.

Question 2

Define community.

Answer 2

All living individuals inhabiting the same area at any given time. Populations are the units of the community.

Question 3

Define species.

Answer 3

Individuals that are able to interbreed to produce fertile offspring. Members of the same species generally have similar characteristics to one another.

Question 4

What does the other criteria for defining a species include?

Answer 4

• Members of the same species are similar biochemically, evident in their DNA base sequences and amino acid sequences.
• Members of the same species share a common gene pool. Species is the largest unit of a population where genetic exchange is possible. Each species has its own gene pool and is reproductively isolated from all other species.
• Morphologic similarity; often members of the same species have characteristics in common.

Question 5

Define gene pool.

Answer 5

The sum of all genes (alleles) of all the individuals in a population from which future generations of individuals will be created.

Question 6

Define reproductive isolation.

Answer 6

Inability of related species to interbreed due to biological features of the organism.

Question 7

What are prezygotic reproductive barriers?

Answer 7

Prevents fertilisation. These comprise temporal, gamete, behavioural and mechanical isolation.

Question 8

Define temporal isolation.

Answer 8

Prezygotic reproductive isolation mechanism. This refers to time, and may refer to each species producing its gametes in different seasons, or species living in the same place but are nocturnal (active at night) or diurnal (active during the day).

Question 9

Define gamete isolation.

Answer 9

Prezygotic reproductive isolation mechanism. Fertilisation is prevented even if gametes are transferred. Male gametes may die due to unfavourable conditions, or the gametes may fail to recognise each other. Sperm is destroyed is reproductive tract, sperm is unable to penetrate the ova (egg) or zygotes fail to develop (unequal numbers of chromosomes or genes are too different).

Question 10

Define behavioural isolation.

Answer 10

Prezygotic reproductive isolation mechanism. Mating behaviour (visual, audible, olfactory or courtship) may be sufficiently different so as to fail to attract a mate.

Question 11

Define mechaical isolation.

Answer 11

Prezygotic reproductive isolation mechanism. Anatomical differences in the reproductive structures do not allow for fertilisation to occur.

Question 12

What are postzygotic reproductive barriers?

Answer 12

Prevents the development of fertile hybrids. These comprise hybrid unviability and hybrid sterility.

Question 13

Define hybrid unviability.

Answer 13

Postzygotic reproductive isolation mechanism. Young fail to reach sexual maturity.

Question 14

Define hybrid sterility.

Answer 14

Postzygotic reproductive isolation mechanism. Offspring are infertile.