Slides in this set
What is Genetic Diversity?
Genetic diversity refers to the diversity (or genetic variability) within
species. It refers to the total number of genetic characteristics in the
genetic makeup of a species.
Why are organisms different from one another?
· Similarities & differences b/w organisms may be defined in terms of
variation in DNA.
· It is proteins which makes organisms different and it is DNA which
determines the variety of proteins that make up each organism.
· Hence it is the differences in DNA that lead to the vast genetic
diversity we find on Earth.…read more
All members of the species have the same genes.
· Example: All humans have a gene for blood group. Which blood
group humans have depends on which two alleles of the gene they
· Organisms differ in their alleles not in their genes.
· It is the combination of alleles they possess that makes species
different from one another.
· The greater the number of different alleles that all the members of a
species possess, the greater the genetic diversity of that species.
· The greater the genetic diversity, the more likely that a species will
be able to adapt to environmental changes.
· This is because it will have a wider range of alleles and therefore a
wider range of characteristics.
· There is a greater chance that some individual will possess a
characteristic that suits it to the new environmental conditions.
· Genetic diversity is reduced when a species has fewer different
· Selective breeding (artificial selection) is the process of breeding
plants and animals for particular genetic traits.
· It involves identifying individuals with the desired characteristics
and using them to parent next generation.
· Offspring that do not exhibit the desired characteristics are killed, or
atleast prevented from breeding. In this way alleles for unwanted
characteristics are bred out of the population.
· Selective breeding is commonly carried out to produce high-
yielding breeds of domesticated animals & strains of plants.…read more
Artificial selection has enabled the cultivation of new crops with
desirable traits from one single common ancestor. The Brassicas
(cabbage, broccoli, cauliflower, brussels sprouts, collards and kale)
are great examples of artificial selection.…read more
Selective Breeding in Cattle
· Cattle have been selectively bred for two main purposes.
· For meat Beef breeds high muscle to bone ratio & rapid growth
· For milk dairy breeds high production of milk with a high fat and
protein content, an udder that suits the milikng machine and rapid
delivery of milk
· Rapid change in cattle characteristics has raised a number of issues:
- genetic diversity of cattle has been reduced
- mastitis (inflammation of udder) & infertility as a result of doubling
the milk yield per cow
- most cows now go for slaughter after 5 years (natural life span of a
cow is 25 years !!!)
- calves normally suckle for 6-12 months but nowadays they are
removed from mothers within 2-3 days (to get milk for human use