Download lesson 1 Variation

Variation and adaptation
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Objectives
Know what is variation?
Understand why it is significant?
Explain how variation arise?
Understand that variation leads to
adaptation
• Variation - the presence of
variety/differences between individuals.
• Variation can occur within (intra) a species or
between (inter) species.
• There are 2 main causes of variation:
– Genetic
– Environment
• There are 2 types of variation:
– Continuous
– Discontinuous
Genetic Variation
• What are alleles?
• Alleles are different forms of the same
gene
• e.g. the gene for eye colour may be a
blue allele or a brown allele but it is still
eye colour
• All organisms have a different
combination of alleles
Where does genetic variation
come from?
• In sexually reproducing organisms it
comes from events in meiosis
• Crossing over during prophase 1
• Independent assortment during
metaphase
• Random fusion of gametes
• It may also arise from random
mutations in the DNA
Environmental Variation
• Not all genes are active at once
• Environment can effect which genes are
active at any one time
• Food – obesity
• Sun – skin colour
• Environmental variation can not be
inherited
Discontinuous variation
• Two or more distinct
categories with no
intermediate values.
• Members of a
species may be
evenly or unevenly
distributed between
categories.
• Sex – M or F
• Human blood groups
– A, O, B, AB
Discontinuous Variation
• Usually categorical (has a label assigned
rather than a number)
• Primarily due to genetic variation and
very little influence of environment
• Usually determined by a single gene with
only 2 or 3 possible alleles
Continuous variation
• There are two
extremes and a full
range of
intermediates.
• Most individuals are
close to the mean
value.
• The number of
individuals at the
extremes are low.
• E.g. Height in humans
or length of leaves on
a tree.
Continuous Variation
• Can be due to genetics and/or
environment
• Usually a result of the combination of
many different genes and alleles and
then affected by environment too
• Often assigned numerical values but not
always, like eye colour and skin colour
Adaptations
An adaptation is a
feature that
enhances survival and
long term
reproductive success.
A well adapted organism will be able to:
Find enough food or photosynthesise well
Find enough water
Gather enough nutrients
Defend itself against predators and diseases
Survive the physical conditions of its
environment such as changes in temperature,
light and water levels
• Respond to changes in its environment
• Have enough energy left over to reproduce
successfully.
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Behavioural Adaptations
Earthworms will retract into their burrows if you
touch them – adaptation to not being eaten by
birds.
Physiological Adaptations
Saccharomyces can respire sugars
aerobically or anaerobically
depending on the supply of oxygen
Anatomical Adaptations
Legionella bacteria have flagella to help
them move independently.
Adaptations of xerophytes
Behavioural:
• Close stomata to reduce water loss
• Folding leaves to trap humid air
• Open stomata, leaves wilt, reduces SA
exposed
Physiological
The mechanisms that allow for stomatal
opening and closing
Marram Grass
Reduced
Fleshy
leaf size
Specialists
stem
or at living on sand dunes
leaves
Leaf rolled up to trap air inside
Thick waxy cuticle to reduce
water evaporation from
surface
Trapped air inside with high
water vapour potential
Hairs on lower surface reduce
movement of air
Extensive
roots
Stomata in pits to trap air with
moisture close to the stomata
Summary of Xerophyte Adaptations
Adaptation
Smaller leaves shaped like
needles.
Densely packed spongy
mesophyll
Thicker waxy cuticle
Closing of stomata
Hairs on the surface of the leaf
Pits containing stomata at the
base
Rolling of leaves
Low water potential inside leaf
cells.
How it Works
Example