Cell Cycles

Question 1

Features of prophase…

Answer 1

-nuclear membrane begins to breakdown
- centrioles move to poles
- chromatin supercools and condense in chromosomes

Question 2

Features of metaphase…

Answer 2

• spindle fibres form
• spindle fibres attach
• to centromere of chromosomes
• chromosomes align at equator

Question 3

Features of anaphase…

Answer 3

• spindle fibres shorten
• centromere splits
• sister chromatids separated
• chromatids pulled to opposite poles of cell

Question 4

Features of telophase…

Answer 4

• nuclear membrane begins to reform
• chromosomes unwind

Question 5

What are homologous pairs of chromosomes?

Answer 5

• two chromosomes that carry the same genes in the same loci

Question 6

What should be done when counting cells to make sure mitotic index obtained is accurate?

Answer 6

• examine large number of cells
• for representative sample
• repeat count
• ensure figures are correct
• method to deal with parts shown at edge
• standardise counting

Question 7

Differences between mitosis and meiosis.

Answer 7

Mitosis
- one division
- daughter cells genetically identical
- 2 daughter cells
- diploid
- no crossing over
- no independent segregation

Meiosis
- two divisions
- daughter cells genetically non-identical
- 4 daughter cells
- haploid
- crossing over
- independent segregation

Question 8

How does meiosis result in haploid number of chromosomes and genetic variation?

Answer 8

• homologous chromosomes pair up
• maternal and paternal chromosomes arranged in ANY order
• independent segregation
• crossing over
• new combo of alleles

Question 9

Process of crossing over…

Answer 9

• homologous pairs of chromosomes associate
• chiasmata form
• alleles exchanged
• new combo of alleles

Question 10

Process of independent segregation…

Answer 10

• maternal and paternal chromosomes reshuffle in any combination
• new combo of alleles

Question 11

Process of meiosis…

Answer 11

• DNA replication in late interphase
• two divisions
• separation of homologous chromosomes
• separation of sister chromatids
• produces 4 genetically non-identical haploid cells

Question 12

Describe binary fission…

Answer 12

• replication of circular DNA
• replication of plasmids
• division of cytoplasm

Question 13

What happens during interphase?

Answer 13

• G1 = increase in cell size
• S phase - Semi-conservative replication
• G2 = synthesis and stores of ATP, synthesis of organelles

Question 14

What occurs at cytokinesis - mitosis?

Answer 14

• cytoplasm divides producing 2 genetically identical diploid cells

Question 15

What is a tumour?

Answer 15

• mass of cells
• by uncontrolled cell division

Question 16

How would you determine a reliable mitotic index?

Answer 16

• count cells in mitosis field of view
• divide this by total number of cells in field of view
• repeat many times