Cell Division Study Guide

1. Draw and label the cell cycle.

2. What is happening to the cell during interphase? (see below)

3. Draw a picture of a replicated chromosome (see chromosome on right). 4. Draw a picture of a non-replicated chromosome (see left).

Sister chromatids

Non-replicated Replicated

5. What does diploid mean? What type of cell in your body is diploid?

• A cell that contains both sets of homologous chromosomes is said to be diploid, which means “two sets”. The number of chromosomes in a diploid cell is sometimes represented by the symbol 2N.

• For Drosophila (fruit fly), the diploid number is 8, which can be written 2N = 8.

• All cells EXCEPT sex cells are diploid. These are called somatic cells.

6. What do you call each pair of chromosomes in a diploid cell? Is each chromosome similar or identical?

• A pair of chromosomes in a diploid cell are called HOMOLOGOUS.

• One member of the homologous pair comes from your Mom – the other comes from Dad. They are not identical, but they DO carry similar sequences of DNA!

7. What does haploid mean? What type of cell in your body is haploid? What are two examples of

gametes?

• Haploid means “one set”. For Drosophila (fruit fly), this can be written as N = 4.

• Haploid cells in the body include gametes, or sex cells. Two examples: sperm cells (males) and egg cells (females).

8. What type of cell undergoes meiosis to produce gametes? Where are these cells found?

• Sperm producing cells in males are found in the testes.

• Egg producing cells in females are found in the ovaries.

• Both of these cells undergo meiosis in order to produce haploid (N) egg and sperm cells.

9. Define mitosis. List the 4 phases of mitosis.

Reproduction by mitosis is classified as asexual, since the cells produced by mitosis are genetically identical to the parent cell. Mitosis is also a source of new cells when a multicellular organism grows and develops.

10. If the diploid number of replicated chromosomes is 24, how many chromosomes would you find in the egg cell of this animal?• Answer: 12

• Answer: 48 chromatids, 24 centromeres

11. If the diploid number of replicated chromosomes is 24, how many chromatids would there be? How many centromeres?

12. In meiosis, the parent cell (germ cell) has a diploid number of chromosomes, and the resulting daughter cells have a ________ number of chromosomes.

• haploid

13. What is separating in meiosis I?

• Homologous chromosomes (replicated).

Draw the diagrams.

• For questions 13 – 16, use your textbook, pg. 276-277 to draw the chromosomes during meiosis I.

17. What is separating in meiosis II?

• The 2 cells produced by meiosis I now enter a second meiotic division. Unlike the first division, neither cell goes through a round of replication before entering meiosis II.

• Each of the cell’s chromosomes has 2 chromatids. During metaphase II, chromosomes line up in the center of the cell. In anaphase, the paired chromatids separate.

18. When a sperm (1N) fertilizes an egg (1N), what is the chromosome number of the resulting zygote (haploid or diploid)?

• Answer: Diploid (2N)

19. How many chromosomes do humans have in a somatic cell? In a gamete/sex cell?

• Answer: Somatic cell: 46 chromosomes, Gamete: 23 chromosomes.

20. Fill in chart:

MITOSIS MEIOSIS

Chromosome # of parent cell

diploid diploid

# of daughter cells 2 4

Chromosome # of daughter cells

diploid haploid

Genetic content of daughter cell

identical variable

Compare mitosis & meiosis.

21. What is spermatogenesis? How many sperm are produced from each germ cell?

• Production of sperm cells. Number of sperm produced: 4

22. What is oogenesis? How many eggs are produced from each germ cell?

• Production of egg cells. Number of eggs produced: 1

Compare spermatogenesis & oogenesis:

23. What is nondisjunction? List and describe 3 chromosomal disorders caused by nondisjunction.

• Nondisjunction is when homologous chromosomes fail to separate.

• Three examples: • Down’s syndrome (trisomy 21) or 3 copies of chromosome 21.• Kleinfelter’s syndrome (males): sex chromosomes are XXY, instead

of XY.• Turner’s syndrome (females): sex chromosome is X-, instead of XX.

Chromosomal disorders

Down’s syndromeTrisomy-21

Kleinfelter’s syndromeXXY

Turner’s syndromeXO

24. How does meiosis cause genetic variation?

• As homologous chromosomes pair up and form tetrads in meiosis I, they exchange portions of their chromatids in a process called crossing-over. Crossing-over produces variability in the 4 haploid chromosomes produced at the end of meiosis.