What can go
wrong in the
cell cycle?
Background: copyright cmassengale
1
Standard
• SB2. Students will analyze how
biological traits are passed on to
successive generations.
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d. Describe the relationships between changes in DNA and
potential appearance of new traits including
Alterations during replication.
– Insertions
– Deletions
– Substitutions
Mutagenic factors that can alter DNA.
– High energy radiation (x-rays and ultraviolet)
– Chemical
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Essential Question
• Why must organisms be able to
grow and reproduce?
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Cell Cycle Errors
• Most errors occur during cell division and the
synthesis stage of interphase
• Causes of Errors:
1. DNA base pairing mistakes during replication
(S stage mistakes)
2. Mutagenic factors: Environmental factors that cause
a mutation
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Ex:
Ex:
Ex:
Ex:
Ex:
carcinogens (Cancer causing agents such as smoking)
High Energy Radiation (alpha, beta and gamma rays)
Ultraviolet Radiation (i.e. Skin Cancer)
X-Rays (doctor’s office)
Chemicals (formaldehyde)
3. Nondisjunction
• When homologous chromosomes or sister chromatids
do not separate during cell division (mitosis or meiosis)
– Can lead to genetic disorders if occurs during Meiosis
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» Ex: Trisomy 21 (Down Syndrome)
Nondisjunction disorders
Normal male karyotype
Trisomy 21- Male
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Nondisjunction Disorders
Klinefelter male
Karyotype
• Klinefelter syndrome:
XXY males. 47
chromosomes. Male sex
organs; unusually small
testes, sterile. Breast
enlargement and other
feminine body
characteristics. Normal
intelligence
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• DNA Base pairing mistakes (Synthesis)
– DNA Replication isn’t always done perfectly.
– Enzymes proofread and correct these mistakes
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• EX: DNA polymerase will check the newly made
DNA strand for errors
3 main types of replication errors:
– Insertions
• Nucleotide added
• Causes a Frameshift mutation
– Deletions
• Nucleotide removed
• Causes a Frameshift mutation
– Substitutions
• Nucleotide replaced
• Causes a missense mutation
• Result
• Nothing
• Cancer
• Producing the wrong protein
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copyright cmassengale
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Deletion Disorder
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Deletion: a portion of one
chromosome is lost during cell
division.
Male Karyotype with
Chromosome 5 deletion
– That chromosome is now missing
certain genes. When this
chromosome is passed on to
offspring the result is usually
lethal due to missing genes
•
Ex:Cri du chat (Cry of the
Cat) A specific deletion of a small
portion of chromosome 5; these
children have severe mental
retardation, a small head with
unusual facial features, and a cry
that sounds like a distressed cat.
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Check for
Understanding
•Directions: Label the top of your paper as ‘Checking for
Understanding’. Put today’s date as indicated below. Write the
questions and the answer to the following questions:
•Date and title
1. What enzyme proofreads for DNA replication?
2. Read about nondisjunction. What phase in cell division
would nondisjunction occur?
3. What can happen if there is a substitution error in DNA
replication?
•Keep this paper in your notes until the next ‘Check for
Understanding’. This is for a grade!