The Cell Cycle and Cell Division

Question 1

What is binary fission?

Answer 1

Cell division in prokaryotic cells

Question 2

What are the three phases of eukaryotic cell division?

Answer 2

Interphase, mitosis and cytokinesis.

Question 3

Can chromosomes be resolved by light structures?

Answer 3

no

Question 4

How do chromosomes appear under a light microscope?

Answer 4

like diffuse structures: chromatin.

Question 5

What are the 5 important features of chromosomes?

Answer 5

1. Characteristic Shape
2. Homologous pairs
3. Fixed number between species.
4. Homologous chromosomes may not carry the same alleles
5. Chromosome are copied before mitosis so they appear to have doubled.

Question 6

What is the centromere

Answer 6

The region in between the p and the q ends of the chromosome..
Always in the same position.

Question 7

Whaat is a somatic cell?

Answer 7

Any cell in the body that isn’t a germ cell or an undifferentiated stem cell.

Question 8

What is a homologous chromosome?

Answer 8

A pair of chromosome in a diploid cell that has the same size and shape. They also carry the same genes in the same order, but not necessarily the same alleles.

Question 9

What is a diploid organism?

Answer 9

one that carries two copies of each chromosome

Question 10

How many chromosomes in somatic cells of humans?

Answer 10

46 (22 autosomes diploid + XX or XY)

Question 11

What does karyotype mean?

Answer 11

The number and shape of chromosomes in a somatic cells of a particular organism

Question 12

What does locus mean?

Answer 12

The position a particular gene occupies on a specific chromosome

Question 13

What is an allele?

Answer 13

One of two or more different forms of the same gene

Question 14

What is a chromatid?

Answer 14

The chromosome after DNA replication and before mitosis, when the chromosomes are condensed

Question 15

What are the stages of interphase?

Answer 15

G1, S and G2

Question 16

What happens during G1?

Answer 16

Cytoplasm is active,
New organelles are formed so cytoplasm increases in size,
Cells are biochemically activated to grow
Pre-mRNA is synthesized
Pre-mRNA becomes mature-mRNA

Question 17

What happens during S phase?

Answer 17

Semi-conservative replication occurs
New histones are synthesized and attached to new DNA
Each chromosome becomes two chromatids, attached via the centromere
Growth continues

Question 18

What happens during G2?

Answer 18

More cell growth, preparation for mitosis
Replicated DNA is checked for errors and corrected.
If correction of DNA is not possible, the cell cycle can be halted here.
Cell growth continues by further synthesis of proteins and organelles

Question 19

Stages of mitosis

Answer 19

Prometaphase
metaphase
anaphase
telophase

Question 20

What happens during cytokinesis?

Answer 20

Division of cytoplasm

Two cells formed.

Question 21

What happens in prophase?

Answer 21

Chromosomes increasingly shorten into a super-coiled structure. - become visible as long, thin threads.
Nucleolus disappears and the nuclear membrane breaks down.
Centrioles divide and move to opposite ends of the cell, radiating a network of microtubules which form the spindles.
Spindle fibers attach to the centromeres and begin to contract to move the chromosomes apart

Question 22

What happens in metaphase?

Answer 22

The chromosomes are aligned down a centre.

They line up on the equator of the spindle

Question 23

What happens in anaphase?

Answer 23

The centromere of each chromosome divides
The spindle fibres attached to them shorten, resulting to two chromatids being pulled by their centromeres to opposite poles of the spindle - once separated the chromatids are referred to as chromosomes again

Question 24

What happens in telophase?

Answer 24

The nuclear membrane reforms around both groups of chromosomes at opposite ends of the cell.
Chromosomes decondense

Question 25

What happens in cytokinesis of animals

Answer 25

This is different in animal and plants cells. Animals: A cleavage furrow develops in the middle of the cell Contraction o this furrow 'pinches' the cytoplasm in half, as this happens the organelles become distributed between the two cells.

Question 26

What happens in cytokinesis of plant cells?

Answer 26

Vesicles of the Golgi collect along the equator of the spindle, known as the cell plate. These vesicles secrete a gel-like layer of calcium pectate called the middle lamella. On to this, they secrete transverse layers of microfibers of cellulose, forming the cell wall. More layers of cellulose are added, often at right angles, forming the secondary cell wall. Many cell walls become impregnated with lignin.

Question 27

What does meristem mean?

Answer 27

A group of plant cells that are able to divide by mitosis

Question 28

How many daughter cells does meiosis produce?

Answer 28

4

Question 29

How meiosis daughter cells genetically identical of different?

Answer 29

different.

Question 30

Where does meiosis occur in humans?

Answer 30

Gonads - testes and ovaries

Question 31

what karyotype are the daughter cells produced from meiosis?

Answer 31

haploid

Question 32

What happens during meiosis I?

Answer 32

Homologous chromosomes are separated

Question 33

What happens during Meiosis II?

Answer 33

Chromatids of each chromosome are separated

Question 34

Stages of meiosis in sequence

Answer 34

``` Prophase I (Early) Prophase I (Mid) Prophase I (late) Metaphase I Anaphase I Telophase I Prophase II Metaphase II Anaphase II Telophase II ```

Question 35

Prophase I (Early, mid and late)

Answer 35

E. The replicated chromosomes become condensed - shorter and thicker. M. Homologous pairs align and centrioles duplicate L. Chromosomes repel each other. Sites where chromosomes have broken and rejoined are now visible

Question 36

Metaphase I

Answer 36

Nuclear membrane breaks down Spindles form Bivalents line up at the equator, attached via centromeres

Question 37

Anaphase I

Answer 37

Homologous chromosomes separate | Whole chromosomes are pulled towards opposite poles of the spindle, centromere first.

Question 38

Telophase I

Answer 38

Nucealr membrane reforms around the nuclei. chromosome numbers have halved Chromosomes start to decondense

Question 39

Prophase II

Answer 39

Chromosomes condense | Centrioles duplicatte

Question 40

Metaphase II

Answer 40

Nuclear membrane breaks down Spindles form Chromosomes attach to the spindles via their centromeres at the equator of the spindle

Question 41

Anaphase II

Answer 41

Chromosomes separate at their centromeres

Question 42

Telophase II

Answer 42

Chromosomes decondense | Nuclear membrane reforms

Question 43

What does bivalent mean?

Answer 43

The name given to two homologous chromosomes in a diploid cell when they are seen paired together during meiosis I. As each chromosome is currently present as two chromatids, there are four chromatids in a single bivalent.

Question 44

Non-sister chromatids

Answer 44

Chromatids on different pairs of homologous chromosomes

Question 45

What is a Chiasma?

Answer 45

A point seen during meiosis I at which the non-sister chromatids seem locked

Question 46

What does "crossing over" mean in meiosis?

Answer 46

The process of non-sister chromatids exchange genes following chiasma.

Question 47

What is chromosome translocation?

Answer 47

When part of a chromosome breaks off and rejoins a different chromosome.

Question 48

What is chromosome non-disjunction?

Answer 48

The failure of homologous chromosomes to separate properly during the first division f meiosis, resulting in daughter cells with either too few or too many chromosomes.

Question 49

What does polysomy mean?

Answer 49

Describes a diploid organism with more than two copies of a particular chromosome

Question 50

What does monosomy mean?

Answer 50

Describes a diploid organism with only one copy of a particular chromosome.

Question 51

An example of monosomy in humans

Answer 51

Turners syndrome

Question 52

What is Turner's syndrome? (genetically)

Answer 52

When women only have one copy of the X chromosome

Question 53

An example of polysomy in humans

Answer 53

Downs syndrome

Question 54

What is downs syndrome? (genetically)

Answer 54

Non-disjunction of Chr 21, resulting in three copies, giving them 47 chromosomes in total.