AQA GCSE Biology B1.6 Genetic
Variation and its control
Inheritance
The information that
results in plants and
animals having similar
characteristics to their
parents is carried by genes,
which are passed on in
gametes from which the
offspring develop
The nucleus of a cell contains chromosomes.
The chromosomes carry the genes that control the characteristics of the body.
Different genes control the development of different characteristics of an organism
Differences in the characteristics of individuals of the same kind may be due to differences in:
The genes that they have inherited
The conditions in which they have developed
or a combination of both
Reproduction
There are 2 forms of reproduction:
Sexual Reproduction~ the fusing of male and female gametes
The mixture of the genetic information from two parents
leads to variation in the offspring
This is important for survival as some
characteristics may give offspring a better chance
of survival.
Asexual reproduction ~ no fusion of gametes and
only one individual is needed as the parent
There is no mixing of genetic information and so
there is no variety in offspring.
These genetically identical individuals are known as clones
Cloning
Modern cloning techniques include:
Tissue Culture ~ Taking small groups of cells from a
part of a plant and growing them under special
conditions.
Taking cuttings from older plants and growing them.
Embryo transplants ~ An embryo with unspecialised cells is split
into smaller groups of cells, then the identical embryos are
transplanted into host mothers.
Adult cell cloning
The nucleus of an adult cell e.g a skin cell is removed.
The nucleus from an unfertilised egg cell (ovum) is removed
The nucleus from the adult body cell is inserted into the empty ovum
A small electric shock causes the egg cell to begin to divide to form an embryo
The embryo cells contain the same genetic info as the adult skin cell (as its nucleus was used)
When the embryo has developed into a ball of cells it is placed into the womb of an adult female to continue its development
Dolly the sheep was produced by adult cell cloning in 1997
Benefits of it are:
Could produce genetically
engineered cloned animals to
have valuable proteins in their
milk. These have uses in
medicine.
Could be used to save animals from extinction
Disadvantages of it are:
Concerns about the ethics of it
Cloning limits the variation in a population (limits the gene pool)
Could cause problems for natural selection if the environment changes
Concerned about using the technique to clone humans in the future
Genetic Engineering
Involves changing the genetic makeup of an organism
In genetic engineering genes from humans and other organisms are 'cut out' using enzymes.
The gene is then placed in the chromosome of another organism.
Genes can also be transferred into the cells of animals,
plants or microorganisms in an early sate of development
so that they develop with desired characteristics
New genes can be transferred to crop plants.
Crops that have their genes modified in this way
are called Genetically modified crops (GM crops)
GM crops may be insect or herbicide-resistant and usually have increased yields.