3.C.1 Effect on Phenotype
Watch the following videos
•http://www.bozemanscience.com/mutatio
ns
•http://www.bozemanscience.com/001natural-selection
•http://www.bozemanscience.com/034mechanisms-that-increase-genetic-variation
Changes in genotype can result in
changes in phenotype.
Draw 5 boxes on your paper…
• On the front of your paper fill in the 5 boxes
for 3C1
• On the back of your paper take your own
notes on 3C2
• Turn in your notes when you finish both
A mutation is a change of the nucleotide
sequence of the genome.
Alterations in a DNA sequence can lead
to changes phenotype.
Changes in phenotype result from
changes in the type or amount of the
protein produced.
Amount of Protein
Box #1
• How can mutations change phenotypes?
DNA mutations can be positive,
negative or neutral.
Mutations
Positive
Neutral
Negative
No Change in Phenotype
Confers Selective
Advantage
OR
Phenotype is Selectively
Neutral
Confers Selective
Disadvantage
Whether or not a mutation is detrimental,
beneficial or neutral depends on the
environmental context
Heterozygote advantage: The sickle cell trait can
confer a selective advantage to heterozygote
individuals in areas affected by malaria (plasmodium).
The sickle cell trait is a point mutation,
which changes only one base pair.
Mutations are the primary source of
genetic variation.
Box #2
• Describe how a mutation can be beneficial.
Mutations result from:
• Errors in DNA replication
• Errors in DNA repair mechanisms
• External factors, such as radiation and reactive
chemicals
Errors in mitosis or meiosis can result
in changes in phenotype.
Box #3
• Provide a brief explanation for the 3 ways in
which mutations arise.
New chromosome combinations: triploidy
usually results in a sterile individual because of
unequal pairing of homologous chromosomes
during meiosis.
Changes in chromosome number often result in
human disorders with developmental limitations.
There only three autosomal trisomies that result in a
viable fetus; the others are too devastating, and the
fetus usually dies in utero.
• Trisomy 13: Patau Syndrome
• Trisomy 18: Edward’s Syndrome
• Trisomy 21: Down Syndrome
Trisomy 21: Down Syndrome
XO: Turner Syndrome
Box #4
• Research one of trisomy 13, 18, or 21, and
describe how this occurs
Genetic changes
that enhance
fitness can be
selected for by
environmental
conditions.
Example: Antibiotic resistance
mutations
Example: Pesticide resistance
mutations
Box #5
• How can mutations increase survival (fitness)?
Learning Objectives:
LO 3.24 The student is able to predict how a change in
genotype, when expressed as a phenotype, provides a
variation that can be subject to natural selection.
[See SP 6.4, 7.2]
LO 3.25 The student can create a visual representation to
illustrate how changes in a DNA nucleotide sequence can
result in a change in the polypeptide produced. [See SP 1.1]
LO 3.26 The student is able to explain the connection between
genetic variations in organisms and phenotypic variations in
populations. [See SP 7.2]