calculating genetic biodiversity

Question 1

intro

Answer 1

Maintaining genetic biodiversity is essential to the survival of a species. In isolated populations, such as those present within a captive breeding programme, genetic biodiversity is often reduced. This means that the individuals may suffer from a range of problems associated with in-breeding.
Scientists can calculate the genetic biodiversity of a population of a species (sometimes referred to as the gene pool) to monitor the health of the population and ensure its long-term survival.

Question 2

the importance of genetic biodiversity

Answer 2

Within a species, individuals have very little variation within their DIA.
All members of the species share the same genes. However, they may have different versions of some of these genes. The different
‘versions’ of genes are called alleles. The differences in the alleles among individuals of a species creates genetic biodiversity within the species, or within a population of the species. The more alleles present in a population, the more genetically biodiverse the population.
Species that contain greater genetic biodiversity are likely to be able to adapt to changes in their environment, and hence are less likely to become extinct. This is because there are likely to be some organisms within the population that carry an advantageous allele, which enables them to survive in the altered conditions.
For example, when a potentially fatal new disease is introduced to a population, all organisms will be killed unless individuals carry resistance to the disease. Those organisms are likely to survive the disease, and therefore be able to reproduce - leading to the survival of the species

Question 3

factors that affect genetic biodiversity

Answer 3

For genetic biodiversity to increase, the number of possible alleles in a population must also increase. This can occur through:
• mutation(s) in the DNA of an organism, creating a new allele.
• interbreeding between different populations. When an individual migrates from one population and breeds with a member of another population, alleles are transferred between the two populations. This is known as gene flow.

In order for genetic biodiversity to decrease, the number of possible alleles in a population must also decrease. This can occur through:
• selective breeding (also known as artificial selection), where only a few individuals within a population are selected for their advantageous charactersis and bred. For example, the breeding of pedigree animals or of human food crops
-captive breeding programmes in zoos and conservation centres, where only a small number of captive individuals of a species are available for breeding. Often the wild population is endangered
or extinct

-rare breeds, where selective breeding has been used historically to produce a breed of domestic animal or plant with characteristics which then become less popular or unfashionable, so the numbers of the breed fall catastrophically. When only a small number of individuals of a breed remain and are available for breeding, and all of these animals will have been selected for the specific breed traits, the genetic diversity of the remaining population will be low. This can cause serious problems when trying to restore numbers yet maintain breed characteristics, for example, a Gloucester Old Spot pig must have at least one spot on the body to be accepted into the registry of this rare breed
• artificial cloning (asexual reproduction), for example using cuttings to clone a farmed plant
• natural selection. As a result, species will evolve to contain primarily the alleles which code for advantageous characteristics.
Over time, alleles coding for less advantageous characteristics will be lost from a population, or only remain in a few individuals.
• genetic bottlenecks, where few individuals within a population survive an event or change (e.g., disease, environmental change or habitat destruction), thus reducing the ‘gene pool’. Only the alleles of the surviving members of the population are available to be passed on to offspring
• the founder effect, where a small number of individuals create a new colony, geographically isolated from the original. The gene pool for this new population is small.
• genetic drift, due to the random nature of alleles being passed on trom parents to their offspring, the frequency of occurrence of an allele will vary. In some cases, the existence of a particular allele can disappear from a population altogether. Genetic drift is more pronounced in populations with a low genetic biodiversity.

Question 4

measuring genetic biodiversity

Answer 4

One way in which scientists quantify genetic biodiversity is by measuring polymorphism. Polymorphic genes have more than one allele. For example, different alleles exist for the immunoglobulin gene, which plays a role in determining human blood type - this is therefore defined as a polymorphic gene. The three alleles are:

• IA - resulting in the production of antigen A
• IB - resulting in the production of antigen B
• Iº - resulting in the production of neither antigen

Most genes are not polymorphic. These genes are said to be monomorphic - a single allele exists for this gene. This ensures that the basic structure of individuals within a species remains consistent.
The proportion of genes that are polymorphic can be measured using
the formula:

proportion of polymorphic gene loci=number of polymorphic gene loci/total number of gene loci

(The locus (plural - loci) of a gene refers to the position of the gene on a chromosome.)
The greater the proportion of polymorphic gene loci, the greater the genetic biodiversity within the population.