Download What is Variation? - TGHSLevel1Science

Patterns of
Inheritance:
Variation
Inheritance
• Offspring inherit a mixture of traits
from their parents.
• Some of these traits will be similar to
those of one or both of the parents.
• Some of these traits will be unique to
the offspring.
• All members of a species are slightly
different from one another – this is
called Genetic Variation.
What is Variation?
• Variation refers to the differences
within a population.
• The importance of variation is that
because all individuals in a population
are different, some will be better
prepared to survive a change in the
environment and re-build the population.
What is Variation?
• Environmental changes can wipe out the
entire population if it has little or no
variation.
Types of Variation
• There are two types of variation:
 Continuous
– a range of features can be seen, eg.
height or IQ in humans.
 Discrete or Discontinuous
– two or several distinct features can
be seen,
eg. tongue rolling in humans.
Continuous Variation
• variation that can have many variants
within a range.
• e.g height, hand span, IQ, weight.
• controlled by several genes
Continuous Variation
• Continuous variation follows a “bell-shaped curve”
No. with Trait
Most people somewhere
in the middle
Trait (eg height)
Not so many people
either really
short or really tall.
Discrete Variation
• variation that is usually limited to two
variants.
• e.g. tongue roll or non-roll, attached
earlobe or unattached earlobe.
• controlled by a single gene
Discrete Variation
• Discrete variation follows a pattern
that is well suited to a bar graph
• Some people have one variation some
have the other.
Nonrollers
Rollers
No. of Students
Discrete Variation
Tongue Rolling
Check out Genetic Variation in this
class
In 4 groups take a class list and survey
the class on one characteristic
•
•
•
•
Tongue rolling
Height
Hand span
Ear Lobes
Take your results and graph them
Compare your graph with others in the class
Causes of Variation
There are two main causes of variation:
• The Environment (environmental
variation)
-where you live and how you live (can
change)
• Your Genes (genetic variation)
-the genetic information that you were
given by your parents (unchangable)
Sources Of Variation
• For sexually reproducing organisms,
there are four mechanisms for
generating genetic variation:
– mutation
– independent assortment of
chromosomes
– crossing over between homologous
chromosomes
– random fertilization
Mutations
• These are permanent changes in the
genetic material of an organism.
• This can range in size from a single DNA
base to a large segment of a
chromosome, or even a change in
chromosome number.
• Mutations occur randomly in a
population.
Mutations
• Only a small portion of mutations are
likely to be beneficial to the organism.
• Mutations that occur in body cells are
called somatic mutations and can not
be passed on to offspring.
• Mutations that occur in reproductive
cells can be passed on.