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_Rp1mwotQ

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=PQSvDL0SurE

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=_aIWe8Ydm-Q

• http://www.youtube.com/watch?v=EA0qxhR2oOk&feature=related

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=9MnQxiSJZ4Q

EOC Practice Question