Variation and Genes

Variation and Genes

Variation

•These dogs belong to the same species, just as we all belong to the same species

•However, there can be lots of differences between members of the same species (as we saw with the poodle and the labrador)

  These differences within a species are called variation

There are two factors which cause variation:

The characteristics you inherit from your parents

AND

The environment in which you live

•Some characteristics can be both inherited and environmental, for example:

HEIGHT

Height is mostly determined by inheritance, but there are environmental factors such   as a poor diet which can stunt growth.

In fact, there are only FOUR factors which are not influenced at all by environmental factors.These are eye color, natural hair color, Blood groups i.e A,B,O and AB.

How do we inherit characteristic ?

In our body, there are 23 pairs of chromosomes (so 46 altogether!)

•Egg and sperm cells are the only cells in the body to contain 23 chromosomes – they only have one copy of each pair.

•During fertilisation, these cells join together to form an embryo. This means that inside each cell of the embryo there are 46 chromosomes.

CONTINUOUS AND DISCONTINUOUS VARIATION

•Characteristics that are controlled only by genes are known as discontinuous variations.

•We use the phrase “either/or” when talking about discontinuous characteristics e.g. you either have blue eye or brown eyes or green eyes etc.

•When representing the measurements for these characteristics we use bar charts.

•Characteristics that are controlled by both genes and the environment will create a wide variety of measurements.

•We call this continuous variation.

•Most organisms will have measurements around an average (“norm”) but there will be a few organisms with abnormally higher or lower measurements.

•Due to this when these characteristics are measured and recorded in a graph they create a normal distribution (bell curve)

MUTATIONS

•Mutations are random changes that happen to DNA.

•They can be harmful or helpful and they can affect evolution through survival of the fittest and natural selection.

•Most mutations go unnoticed but a few can affect the characteristics (phenotype) that people show.

•Mutations can also cause variation.  For example there could be a random mutation in the DNA of one identical twin causing them to have a different characteristic to their twin.

How do How do we inherit characteristics?we inherit characteristics?

Variation

Variation