Chapter 6 The Cell Cycle & Cell Division

Question 1

Define chromosomes

Answer 1

A long thin structure of DNA and protein joined at the centromere

Question 2

Define chromatid

Answer 2

One of the two identical copies of a chromosome, joined at the centromere prior to cell division

Question 3

Define centromere

Answer 3

Specialise region of a chromosome where two chromatids join and to Which the microtubules of the spindle attach at cell division

Question 4

How many chromosomes does a human have?

Answer 4

46 (23 pairs)

Question 5

Define diploid

Answer 5

Having two complete sets of chromosomes

Question 6

Define haploid

Answer 6

Having one complete set of chromosomes

Question 7

What are homologous pairs of chromosomes?

Answer 7

The chromosomes in a homologous pair are identical in size and shape and they carry the same genetic loci, with genes for the same characteristics. One chromosome of each pair comes from each parent.

Question 8

What is an example of chromosomes that are not homologous?

Answer 8

The XY chromosomes in male mammals

Question 9

What is the cell cycle divided into?

Answer 9

G1 phase - new organelles are made and the cell grows
S phase - chromosomes duplicate by DNA replication
G2 phase - another growth phase, synthesis of enzymes needed for cell division
M phase - cell division by mitosis/meiosis

Question 10

What is mitosis?

Answer 10

A type of cell division in which the two daughter cells have the same number of chromosomes and are genetically identical with each other and the parent cell.

Question 11

In mitosis, what happens during prophase?

Answer 11

The nuclear envelope breaks down and the centrioles move to opposite poles of the cell.

Question 12

In mitosis, what happens during metaphase?

Answer 12

The spindle of fibres is made. The chromosomes line up along the central line of the cell and attaches to the spindle fibres.

Question 13

In mitosis, what happens during anaphase?

Answer 13

The centromeres split, and he spindle fibres contract. This pulls apart individual chromatids.

Question 14

In mitosis, what happens during telophase?

Answer 14

The separated chromatids are now chromosomes. They group together at opposite poles of the cell and a new nuclear envelope forms round each group.

Question 15

What is cytokinesis?

Answer 15

The cytoplasm divides, sharing the cell organelles between the two newly formed cells.

Question 16

What are the functions for mitosis?

Answer 16

Provides genetic stability - genetically identical cells
Growth - repairs damaged cells and new cells can replace dead cells.
Asexual reproduction

Question 17

What is a problem that can occur with mitosis?

Answer 17

The cell cycle is controlled by genes. Some cells may have oncogenes (genes with the potential to cause cancer), if they become mutated, mitosis won’t be controlled. Cancers are a result of uncontrolled mitosis. Cancerous cells divide repeatedly forming tumours in solid tissue.

Question 18

What is meiosis?

Answer 18

A two stage cell division in sexually producing organisms that produce four genetically distinct daughter cells, each with half the number of chromosomes of the parent cell.

Question 19

In meiosis, what happens during prophase 1?

Answer 19

The chromatids exchange segments of DNA, this is called crossing over creating genetic variation. This genetic recombination produces a new combination of alleles.

Question 20

In meiosis, what happens during metaphase 1?

Answer 20

The spindle of fibres is made. The chromosomes line up along the central line of the cell and attaches to the spindle fibres.

Question 21

In meiosis, what happens during anaphase 1?

Answer 21

The centromeres split, and he spindle fibres contract. This pulls apart the chromosomes from each homologous pair to each pole of the cell. Independent assortment occurs in which either chromosome of homologous pair moves to either pole independently of other homologous pairs, there are 4 possible combinations in which this can happen.

Question 22

In meiosis, what happens during telophase 1?

Answer 22

The nuclear envelope reforms around the haploid group of chromosomes.

Question 23

In meiosis, what happens during cytokinesis?

Answer 23

The division of cytoplasm occurs, making two haploid cells.

Question 24

In meiosis, what happens during prophase 2?

Answer 24

The centrioles separate and organise a new spindle.

Question 25

In meiosis, what happens during metaphase 2?

Answer 25

The chromosomes line up on the equator attaching to the spindle fibres.

Question 26

In meiosis, what happens during anaphase 2?

Answer 26

The centromeres divide and the spindle fibres contract, pulling the chromatids to opposite poles.

Question 27

In meiosis, what happens during telophase 2?

Answer 27

At the poles, the nuclear envelope re-forms.

Question 28

Why are the functions of meiosis?

Answer 28

Generates genetic variation

Keeps the number of chromosomes constant from one generation to the next.