Mitosis and Meiosis SAC revision

Question 1

what is binary fission?

Answer 1

It’s the way that prokaryotes divide. This is a mitotic process. Prokaryotes do not go through the cell cycle.

Question 2

outline the steps in binary fission?

Answer 2

1. Cell elongates and DNA is replicated
2. Cell wall and plasma membrane begin to divide
3. Cross-wall forms completely around divided DNA
4. Cells separate

Question 3

four main reasons why cells need to divide?

Answer 3

1. growth
2. replacement
3. repair
4. reproduction

Question 4

identify and outline what happens in the three steps of interphase?

Answer 4

G1: the cell prepares to divide and grows in size, functioning as normal making proteins
S: each of the 46 chromosomes are duplicated by the cell
G2: the cell is preparing to split into two (prepares for mitosis). organelles replicate in preparation for division

Question 5

what happens in prophase?`

Answer 5

• centrioles replicate, and move to opposite sides of the cell
• chromosomes condensed and visible
• nuclear envelope begins to disintegrate

Question 6

what happens in metaphase?

Answer 6

• spindle fibres form and connect centrioles to chromosomes
• nuclear envelope disappears
• chromosomes align along the metaphase plate

Question 7

what happens in anaphase?

Answer 7

• centromeres split, allowing sister chromatids to separate

- chromatids move towards poles. centromeres first. pulled by motor proteins along the microtubule tracks

Question 8

what happens in telophase?

Answer 8

• spindle fibres disperse
• nuclear envelope reforms
• chromosomes uncoil and become too thin to see
• not in sister chromatids anymore

Question 9

what happens in cytokineses in animals?

Answer 9

a ring of actin forms around the equator of the cell, and then tightens to form a cleavage, which splits the celll in two.

Question 10

what happens in cytokinesis in plants?

Answer 10

vesicles move to the equator, line up and fuse to form two membranes called the cell plate. A new cell wall is laid down between the membranes, which fuses with the existing cell wall.

Question 11

what happens in interphase 1?

Answer 11

chromosomes replicate, each duplicated chromosome consist of two identical sister chromatids attached to their centromeres, centriole pairs also duplicate

Question 12

what is crossing over and when does it occur?

Answer 12

occurs in meiosis when tetrads first form. bits of one chromosome are swapped with the corresponding bits of the other chromosomes of the homologous pair. occurs during prophase 1

Question 13

what is independent assortment and when does it occur?

Answer 13

this happens during metaphse 1. Since the homologous chromosomes can line up in any orientation on the metaphase plate, the maternal and paternal versions of the different chromosomes can be mixed up in the final gametes.

Question 14

what happens in prophase 1?

Answer 14

• homologous chromosomes appear, each made of two chromatids joined at the centromere

Question 15

what happens in metaphase 1?

Answer 15

• spindle forms and homologous pairs line up on metaphase plate

Question 16

what happens in anaphase 1?

Answer 16

• no centromeres split. homologous pairs pulled to opposite ends of the cell

Question 17

what happens in telophase 1?

Answer 17

• nuclear envelope reforms around two haploid cells

Question 18

what happens in prophase 2?

Answer 18

• nuclear membrane starts to break down again
• chromatids still joined at centromeres
• there has been no DNA replication and there is no crossing over

Question 19

what happens in metaphase 2?

Answer 19

• new spindles form and pairs of chromatids line up on metaphase plate

Question 20

what happens in anaphase 2?

Answer 20

• centromeres split and chromatids pulled to opposite ends of the cell by motor proteins on the microtubules

Question 21

what happens in telophase 2?

Answer 21

• nuclear envelope reforms and chromosomes uncondensed giving four haploid cells

Question 22

define mutation

Answer 22

the changing of the structure of a gene, resulting in a variant form which may be transmitted to subsequent generations, caused by the alteration of single base units in DNA, or the deletion, insertion, or rearrangement of larger sections of genes or chromosomes.

Question 23

what are non-disjunction mutations?

Answer 23

• those that involve the whole chromosome
• chromosomes don’t separate properly during the divisions (anaphase) in Meiosis 1 or Meiosis 2
• this can result in downsyndrome and miscarriages

Question 24

what are block mutations?

Answer 24

• those that involve part of the chromosome
• these occur during the crossing over in prophase 1 of meiosis
• results in a new order of genes along a chromosome

Question 25

identify and explain the 5 different block mutations

Answer 25

1. Duplications: a part of the chromosome is copied, resulting in duplicate segments of the same gene
2. Inversions: a segment of a chromosome is removed and then replaced in reverse order
3. Deletions: a portion of a chromosome is lost
4. Insertions: a part of one chromosome is removed and added to another chromosome
5. Translocation: segments of two chromosomes are exchanged, between non-homologous chromosomes