Crossing Over during Meiosis



Sources of Genetic Variation

A. Crossing Over during Meiosis

Directions: Use two different colors to shade the parts of each chromatid belonging to parent chromosomes A and B.

Answer the following questions.

1) In which cells in the body does crossing over occur?

2) During which phase of meiosis does crossing over happen?

3) How many possible combinations of two genes are possible?

4) Why is crossing over beneficial for organisms?

B. Non-Disjunction

5. Describe what went wrong during meiosis below:

6. This is called non-disjunction. It means:

7. Label a monosomy and a trisomy above.

8. What is the effect on the fertilized egg (zygote)?

9. What will that cause in the individual as it grows into an embryo and then adult?

10. Label the zygotes as either: 2n + 1 or 2n – 1

11. What are three human disorders that result from non-disjunction?

C. Independent Assortment

12. Label the stage of Meiosis below.

13. How could these chromosomes lined up differently?

14. What is independent assortment?

15. How does that cause variation?

D. Mutations

16. What is a mutation?

17. When in the cell cycle do mutations occur?

18. If a mutation occurred in a body cell, what would be the affect?

19. If a mutation occurred in a sex cell, what would be the effect?

20. What is a point mutation?

21. What is a frameshift mutation?

22. Which has the greater affect on the resulting protein?

23. What are mutagens? Give some examples?

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A A a a

B b B b

a a

B b

A A

B b

A

B

A

b

a

B

a

b

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