1 This is the study of how characteristics are
passed on from one generation to the next.
1.1 The raw material for genetics is genetic variation.
1.1.1 No two organisms of the same species are identical
(except identical twins).
2 Genetic Variation:
2.1 is that variation that can be passed on
from one generation og organisms to the
next = INHERITED.
2.2 Genetic variation is not to be confused with that vaiation that is
caused by the environment which is not inherited. E.g a muscle builder
does not pass on his big muscles to his offspring. = ENVIRONMENTAL
2.3 : Genetic Variation can be divided into two sorts.
2.3.1 CONTINUOUS: where a characteristic can take a range of
values e.g foot length, lung volume.
2.3.2 DISCONTINUOUS or DISCRETE: all or nothing, this characteristic is
either there or not there e.g fixed or free earlobes. There is no range.
2.4 Variation means having different genes in a
population. This variation can be inheritable
(passed on from generation to generation e.g
height) or envionmental e.g tanned skin.
Variation increases a species chance of
survival in changing environments, because
certain traits are better suited to certain
conditions than others. This means that
species with more variation have a greater
chance of surviving change than those with
3 Structure of DNA:
3.1 DNA is found in the nucleus of cells.
3.2 STRUCTURE: DNA is a molecule shaped
like a twisted ladder - known as a double
3.2.1 The backbone of the "ladder" is made up of a
phosphate group and a sugar (deoxyribose).
126.96.36.199 The 'rungs' of the ladder are made of base pairs.
4 DNA Replication:
4.1 When an organism grows, repairs itself, reproduces or replaces
old cells, new cells need to be made. Every new cell needs it's own
copy of the genetic code (DNA) that is the same as the original. It is
making these new copies of DNA that is called DNA replication.
4.1.1 Each newly formed double helix
is made up of one original (parent)
strand and one newly made
188.8.131.52 This is known as semi -
conservative replication (semi
= half, conservative - to keep
the same) .
4.2 The DNA Replication Process:
1. The DNA double helix
unwinds and the two strands
4.2.1 2. The original strands of DNA
act as templates to make new
strands that match.
184.108.40.206 3. There are now two identical
DNA molecules that wind up
seperately and each will go into
a new cell.
4.3.1 1. Hydrogen bonds are broken between base
220.127.116.11 2. DNA molecule unwinds and unzips:
18.104.22.168.1 3. New molecule nucleotides pair up:
22.214.171.124.1.1 4. Bonds reform and DNA molecule winds up.
5 Cell Division:
5.1 Cells often need to be replaced - because theyve
grown old or died. New cells are made by a from of
celld divison called MITOSIS.
5.1.1 This process happens in all of
your cells, apart from the testes
5.1.2 It creates 2 cells, both individual to
the original, mother cell.
126.96.36.199 This process is completed in a series of steps:
line up singularly
along the middle.
5.2 MITOSIS - the splitting of the replicated
5.3.1 This is the form of cell division that is used to create sex cells
(egg and sperm) in the gametes (testes and ovaries in
5.3.2 Meiosis creates 4 daughter cells, each with 1/2 the number of
chromosomes as the mother cell. This is because at
fertilisation, 2 gametes will come together to create a new cell
(zygote) which has the full number of chromosomes.
188.8.131.52 Meiosis begins with a single cell.
1. Chromosomes condense and
DNA is replicated
184.108.40.206.1 2. The homologous chromosomes
line up along the equator in pairs.
Non- sister chromatids exchange
segmets = crossing over.
220.127.116.11.1.1 3. The homologous
chromosomes are pulled
apart and the cell divides ..
18.104.22.168.1.1.1 4. The chromosomes line up
individually along the equator and
the chromatids are seperated.
22.214.171.124.126.96.36.199 5. The 2 cells divide .. 4
cells. Each has half the
number of chromosomes as