Cell Division

Question 1

G1

Answer 1

-First growth phase
-Cells increase in size
-Genes are transcribed
-Organelles duplicate

Question 2

S phase

Answer 2

-Replication phase
-DNA duplicates in a specific order with genes in all cells being made first.
-Afterwards chromosomes consist of two sister chromatids.

Question 3

G2

Answer 3

-Second growth phase

Question 4

Restriction point

Answer 4

-Between G1 and S
-Where chromosomes are checked for damage.
-If detected they are destroyed or delayed.
-Similar check between G2 and mitosis.

Question 5

G0

Answer 5

-Triggered by differentiating cells or damage.
-Cells undergoes programmed cell death (apoptosis) or is left to die away (senescence)

Question 6

Homologous chromosomes

Answer 6

-Code for the same gene but have different versions of the gene.
-eg male xy to female xx

Question 7

Prophase

Answer 7

-nuclear membrane breaks down and nucleolus disintegrates
-centrioles duplicate and move to each end of the cell. They are joined by tubulin threads.

Question 8

Metaphase

Answer 8

-pairs of chromatids lined up along the metaphase plane of a cell.
-pulled apart by spindle fibres at their centromere

Question 9

Anaphase

Answer 9

-centromeres divide and sister chromosomes are pulled apart.
-Moved apart by motor proteins on tubulin threads.
-Chromosomes now known as chromatids.

Question 10

Telophase

Answer 10

-Nuclear envelope forms around each of the two clusters of chromosomes making two nuclei.
-Chromosomes uncoil.
-Spindle fibres disappear.

Question 11

Cytokinesis

Answer 11

-divides into two identical daughter cells

Question 12

Centrioles

Answer 12

-parts of the cytoskeleton.
-arranged in 9 groups of 3 microtubules

Question 13

Meiosis

Answer 13

-Combining of gametes (mother and father chromosomes) to get a random selection of characteristics.

Question 13

Prophase 1

Answer 13

-Chromosomes thicken and become visible.
-Nuclear envelope breaks down.
-Threads of tubulin form in the centriole.
-Chromosomes from the mother and father come together in homologous pairs.
-Crossing over occurs between them where alleles are shuffled by the swapping of sections.

Question 14

Metaphase 1

Answer 14

-Pair of crossed (bivalent) chromosomes attach along the equator.
-Pairs arranged randomly and face opposite ends of the cell.
-The way they line up determines how they will separate.
-This is known as independent assortment.

Question 15

Anaphase 1

Answer 15

-Each pair of homologous chromosomes are pulled apart by motor proteins.
-Each chromosome consists still of two chromatids.

Question 16

Telophase 1

Answer 16

-Two nuclear membranes form around each set of chromatids.
-The cell divided by cytokinesis.
-In plants this stage is skipped.

Question 17

Prophase 2

Answer 17

-Nuclear envelope breaks down again and spindles form.
-Due to crossing over the chromatids of each chromosome are no longer identical.

Question 18

Metaphase 2

Answer 18

-Chromosomes attach to the equator of the spindle.
-Chromatids are randomly assorted to further mix alleles.

Question 19

Anaphase 2

Answer 19

-Centromeres divide and chromatids are dragged to each pole.
-Chromatids are randomly separated.

Question 20

Telophase 2

Answer 20

-Nuclear envelopes form around the four haploid nuclei.

Question 21

Variation in meiosis occurs due to

Answer 21

-Crossing over shuffling alleles during prophase 1.
-Independent assortment of alleles randomly distributes mother and father in anaphase 1.
-Independent assortment of chromatids during anaphase.
-Random combinations of gametes during fertilisation.
-Random mutations in parts of chromosomes.