Sources of Genetic Variation
How does Meiosis lead to genetic
variation?
What is Crossing Over?
• Crossing over is when homologous
chromosomes EXCHANGE genetic information
to create genetic DIFFERENCES!
When does it happen?
• ONLY during MEIOSIS!
What does it mean?
• It means that one person can NEVER make the
same EGG or SPERM cell!
What does it look like?
Video Clip
• http://www.youtube.com/watch?v=5x_Rp1
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What is Random (Independent)
Assortment of Chromosomes?
• Random assortment of chromosomes means
that it is completely RANDOM which
CHROMOSOMES go into which gametes.
When does it happen?
• ONLY during MEIOSIS!
What does it mean?
• All gametes are genetically DIFFERENT!
What does it look like?
Video Clip
• http://www.youtube.com/watch?v=PQSvDL0
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What are Mutations?
• A Mutations is when there is a MISTAKE in the
DNA sequence.
What can it be?
• Mutations can be BAD, GOOD or NEUTRAL!
What happens in a BODY cell?
• The mutations will ONLY affect that PERSON
What happens in a SEX cell?
• The mutation can be passed onto the
offspring!
What does it look like?
What is Non-Disjunction of
chromosomes?
• Non-Disjunction is when chromosomes FAIL to
separate from each other
When does it happen?
• During MEIOSIS!
What does it result in?
• It results in the WRONG number of
CHROMOSOMES in each cell.
What are two famous examples?
1. Down Syndrome
– 3 chromosomes at # 21
2. Klinefelters Syndrome
– an extra X chromosome (XXY instead of XY)
What does it look like?
Video Clip
• http://www.youtube.com/watch?v=_aIWe8Y
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• http://www.youtube.com/watch?v=EA0qxhR
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What is fertilization?
• Fertilization is when an EGG and SPERM come
together.
What does it create?
• They create 100% UNIQUE combination of
genes!
What does it look like?
Video Clip
• http://www.youtube.com/watch?v=9MnQxi
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EOC Practice Question