what do genes do - phenotype - characteristsics
the characteristics of an organism, such as its height, shape, blood group or sex are known as its phenotype
differences in pheneotype amond a species are caused by differences in:
- genetic make-up or gentype
- the enviroment in which the organism develops
some characteristsics for example the organisms blood group are only affected by its gentype and the enviroment has little or no affect. such characteristsics are controlled by genes at a single locus and show discontiuous variation.
characteristsics that are affectted
in monohybrid inheritance each locus is responsible for a different heritable feature, however most inherited characteristics are not determined by just one locus but involved interaction of many loci.
when a number of genes are involved in the inheritence of a characteristsic we call the inheritence polygenic.
conditions where several genetic and one or more enviromental factors are involved are said to be multifactorial.
genes and enviromental interactions
there are many many example of genes and the enviroment interaction to produce an organisms phenotype, for example:
- hair colour
- causes of cancer
phenotype - height
the following are some possible answers to why height increases from generation to generation
- taller men have more children
- movements of people around the world means less inbreeding. leading to taller people
- better nutrition
- improved health
hair colour - making melanin - phenotype
the dark pigment in hair is called melanin which is made in melanocytes found in the skin and at the root of the hair in the follicle.
these are activated by melanocyte-stimulating hormone (MSH) , which have receptors on the surface of melancyte cells.
these melanocytes place melanin into organelles called melanosomes. the melanosomes are transfered to nearby skin and hair cells where they colect around the nucleus, protecting the DNA from harmful UV light. meaning people with darker skin have more receptor and have greater protecting from UV light.
UV light increases the amount of MSH and MSH receptors making the melanocytes more active and causing the skin to darken..
on the other hand hair becomes lighter due to the destruction of the melanin by UV light.
more on melanin
to make melanin animals use an enzyme called tyrosinase
this catalyses the first step changing the amino acid tyrosine into melanin.
monoamine oxidase A is an enzyme that catalyses the breakdown of a neurotransmitter in the brain involved in the regulation of behaviour.
it was discovered that ome induviduals have a rare mutation in the MAOA gene and produce no enzyme. they exibit agressive and sometimes violent behaviour.
this issue led to a connection between genes and violoent behaviour but studies did not show a clear link