But even organisms of
the same species will
usually look at least
slightly different
These differences are called the
variation within a species and there
are two types of variation: genetic
variation and environmental variation
Different genes cause genetic variation
1. All plants and animals have characteristics that
are in some ways similar to their parents
2. This is because an organisms characteristics are
determined by the genes inherited form their parents
3. These genes are passed on in sex cells
(gametes) which the offspring develop from
4. Most animals get some genes from the mother
and some from the father.
5. This combining of genes from two parents
causes genetic variation no two of the
species are genetically identical
6. Some characteristics are determined only by
genes. In animals these include: eye colour, blood
group etc
Characteristics are also influenced by the environment
The environment that organisms live and grow in also
causes differences between members of the same
species this is called environmental variation
Environmental variation covers a wide range of
differences from losing toes in a piranha attack to getting
a sun tan to having yellow leaves etc
Basically any difference that has been
caused by the conditions something lives in
is an environmental variation
Most characteristics are due to genes
and the environment
Most characteristics e.g. body weight
are determined by a mixture of genetic
and environmental factors
For example the maximum height that
an animal or plant could grow to is
determined by its genes. But whether it
actually grows that tall depends on its
environment
Genes, Chromosomes and DNA
1. Most cells in your body have a
nucleus. The nucleus contains your
genetic material in the form of
chromosomes
2. The human cell nucleus
contains 23 pairs of
chromosomes
3. Chromosomes carry genes.
Different genes control the
development of different
characteristics
4. A gene is a short length of the
chromosome which is quite a long length of
DNA. There can be different versions of
the same gene which give different version
of a characteristic like brown or blue. The
different versions of the same gene are
called alleles instead of genes
5. The DNA is coiled up to form the arms of the chromosomes
Sexual reproduction
Sexual reproduction produces genetically different cells
1. Sexual reproduction is where genetic
information from two organisms (a father and
mother) is combined to produce offspring
which are genetically different to either plant
2. In sexual reproduction the mother and the
father produce gametes e.g. egg and sperm
cells in animals
3. In humans each gamete contains 23 chromosomes half the number of chromosomes in a normal cell.
4. The egg and the sperm cell then fuse together
(fertilisation) to form a cell with the full number of
chromosomes
5. This is why the offspring inherits features
from both parents its received a mixture of
chromosomes from its mum and its dad
6. This mixture of genetic material
produces variation in the offspring
Sexual reproduction involves
the fusion of male and female
gametes. Because there are two
parents the offspring contain a
mixture of their parents genes
Asexual reproduction
1. An ordinary cell can make a new cell by
simply dividing in two. The new cell has
exactly the same genetic information as
the parent cell
2. X-shaped chromosomes have two identical
halves. So each chromosome splits down the
middle to form two identical sets of half
chromosomes. A membrane forms around each
set and the DNA replicates itself to form two
identical cells to complete sets of X shape
chromosomes
3. This is how all plants and animals grow and produce replacement cells
4. Some organisms also produce offspring using asexual reproduction e.g. bacteria
In asexual reproduction theres only one parent.
Theres no fusion of gametes no mixing of
chromosomes and no genetic variation between
the parent and offspring. The offspring are
genetically identical to the parent