These are detailed Revision Notes for Topic Six (Inheritance, Variation and Evolution) of AQA GCSE Biology. They are written by me, using a combination of class notes, text books and revision guides. I have also uploaded the other chapters in my store.
Inheritance, Variation and
Evolution
Sexual and Asexual Reproduction:
Sexual reproduction involves the fusion of male and female gametes.
Because there are two parents, the offspring contain a mixture of their
parents’ genes.
In asexual reproduction there’s only one parent. There’s no fusion of
gametes, no mixing of chromosomes and no genetic variation between
the parent and the offspring. The offspring are genetically identical to
the parent – they’re clones
Sexual Asexual
Number of 2 1
parents
Type of Meiosis Mitosis
division
Advantages Produces variation Only 1 parent
in the offspring needed.
If the environment More time and
changes variation energy efficient
gives a survival No need to find a
advantages for the mate
species by natural Faster
selection. Many genetically
Selective breeding identical offspring
by humans can produced in
speed up the favourable
process of natural conditions (can
selection. spread/colonise an
Increased food area)
production. If one is well
adapted to habitat,
all will be
Some organisms can reproduce both sexually and asexually
depending on the conditions
o Malaria reproduces sexually when it’s in a mosquito and
asexually when it’s in a human host
o Fungi release spores which can become new fungi when they
land in a suitable pace. Spore can be produced sexually and
asexually.
o Plant produce seeds sexually, but some can also reproduce
asexually e.g. strawberry plants produce runners. These are
stems that grow horizontally on the surface of the soil away from
, a plant. At various points along the runner, a new strawberry
plant forms that is identical to the original plant. Another
example is plants that grow from bulbs. New bulbs can form from
the main bulb and divide off. Each new bulb can grow into a new
identical plant.
Meiosis:
Gametes are formed by meiosis; they only have one copy of each
chromosome so that when gamete fusion happens, they have the right
amount again.
Meiosis contains 2 divisions and in humans it only happens in the
reproductive organs.
o Before the cell starts to divide, it duplicates its genetic
information, forming two armed chromosomes – one arm of each
chromosomes is an exact copy of the other arm. After replication,
the chromosomes arrange themselves into pairs.
o In the first division in meiosis the chromosome pairs line up in
the centre of the cell.
o The pairs are then pulled apart, so each new cell only has one
copy of each chromosome. Some of both the mother’s and
father’s chromosomes go into each cell.
o In the second division, the chromosomes line up again in the
centre of the cell. The arms of the chromosomes are pulled apart.
You get 4 gametes, each with only a single set of chromosomes in it.
Each of the gametes is genetically different from the others because
the chromosomes all get shuffled up during meiosis and each gamete
only gets half of them.
Mitosis Meiosis
Roles within living Growth To produce gametes
organisms Repair
Asexual reproduction
Where it occurs All body cells In the gonads
Number of 1 2
divisions
Chromosome Same Half
number in
daughter cells
compared to
parent cell
Genetic similarity Identical Genetically different
of daughter cells to
parent cells
Number of 2 4
daughter cells
DNA:
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