The
differences between individual organisms of the same species
is called variation.
Variation
can be caused by:
Genetic
factors
Environmental
factors
Genetic
variation can be caused by:
Mutations
Fertilisation
Some
variations caused by genetic variation include:
hair colour, eye colour, attached or detached ear lobes and
skin colour. Genetic mutation caused the variations seen in
the photos below. An excellent introduction to this module is
given on the Science
Museum Website.
Intelligence,
Sporting Ability and our Health are governed by both environmental
factors and genetic factors. There
is a lot of debate in the scientific community over the relative
importance of each of these. Examples are give in the table
below.
Environmental Factors
Genetic Factors
Intelligence
Education and upbringing (e.g. if both parents play a
musical instrument the child may be more likely to)
The physical structure of our brain.
Sporting Ability
Coaching, Practising the sport and the facilities available
(e.g. if you have nowhere to swim you are unlikely to improve
your swimming ability).
Coordination and body structure.
Health
Diet, Exercise, Smoking and Drinking
Genes which contribute to some disorders, e.g. heart disease,
breast cancer.
Each
human cell (except the sex cells) contain 46 chromosomes. Chromosomes
contain genes which are the genetic instructions.
If a gene becomes damaged by a mutation it
is normally harmful and might cause a disease such as cancer.
Mutations happen when a gene becomes damaged in some way. Genes
are made of a chemical called DNA which carries
the genetic code. If there is a change in the genetic code within
the DNA this may cause a mutation. Mutations in the DNA can
happen spontaneously within the cell (especially during cell
division) or may be caused by environmental
factors such as:
nuclear
radiation
chemicals
ultra-violet
rays and X-rays
In the
example shown below there is a small change to the genetic information.
The mutation may cause a disease.
Most
mutations are harmful. However, some mutations may give an advantageous
characteristic to the individual. Every cell contains all of
the instructions about how all cells work. However, not all
of the genes are used in every cell e.g. a nerve cell has a
different set of genes working to a ciliated epithelial cell.
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2005 drparry.co.uk. All Rights Reserved.
