Download Variation is extensive in most populations*

13.11 to 13.15


Traits controlled by
genes alone
Blood Type –
determined by the
genes that produce
antigens which are
present on your Red
Blood Cells
Heritable Variation


Traits controlled by
both genes and the
environment
Height in humans –
determined by
polygenic inheritances
and influenced by your
environment (proper
nutrition, etc…)
Nonheritable Variation

Referring to a
population in which
two or more physical
forms are present in
readily noticeable
frequencies

Garter snakes living in
the same field can have
several different body
colorations. The
behavior of each form
correlates to the body
coloration. Spotted
snake blends in, doesn’t
flee when approached.
Stripped snake flees
rapidly – stripes make it
difficult to judge speed
of motion.
Example

A gradation in an
inherited trait along a
geographic continuum;
variation in a
population's
phenotypic features
that parallels an
environmental gradient
Cline

Body size of many
birds and mammals
tends to increase with
increasing latitude in
North America. Large
size in colder latitudes
reduces the ratio of
body surface area to
volume and helps
conserve heat.
Example



Changes to DNA in
gametes can be passed
to offspring and
potentially impact a
populations gene pool
Can be helpful,
harmful or neutral
Occur often in bacteria
Mutation

Variation that results
from
◦ crossing over (during
prophase 1 of meiosis)
◦ independent
assortment of
homologous
chromosomes ( during
metaphase 1 of
meiosis)
◦ random fertilization
Sexual Recombination


http://www.pbs.org/wgbh/evolution/library/
01/2/quicktime/l_012_02.html
http://www.pbs.org/wgbh/evolution/library/
01/5/quicktime/l_015_03.html