Topic 4: The Cell Cycle

Question 1

Gametes

Answer 1

23 different chromosomes = haploid (n)

includes ova (eggs) + sperm

• sex cells

Question 2

Somatic Cells

Answer 2

includes all cells of body except cells undergoing/resulting from meiosis

eg: muscle cell, nerve cell, etc.

46 chromosomes = diploid (2n)

= 23 homologous pairs

soma= body

Question 3

Homologous Chromosomes

Answer 3

a chromosome pair (1 from each parent) that are identical in length, centromere position, and have genes for the same trait (e.g. eye colour) in the same location (locus)

Question 4

Gene

Answer 4

a unit of heredity
= a region of DNA which contains information for synthesis of proteins

*how we pass on genetic info from one person to the next

Question 5

alleles

Answer 5

different	versions (alleles)	of	that	gene that code for													
different	versions	of that trait.

§ e.g. blue eyes (chromosome from Dad), brown eyes
(chromosome from Mom)

Question 6

What does each somatic cell contain?

Answer 6

23 different chromosome pairs

23 chromosomes from mom (ovum) paired with 23 chromosomes from dad (sperm)

= 46 chromosomes (diploid/2n somatic cell)

Question 7

autosomal chromosomes (autosomes)

Answer 7

1 to 22

¦ contain genes for somatic characteristics

¦ e.g. hair and eye colour, height, etc

¦ each autosomal chromosome pair is not identical, but
equivalent= homologous chromosomes

Question 8

sex chromosome

Answer 8

23
¦ contain genes that determine sex, XX=F XY=M

¦ X or Y from Dad

¦ X from Mom

Question 9

What is the purpose of mitosis?

Answer 9

for growth + repair of tissues

to produce somatic cells

Question 10

What does mitosis result in?

Answer 10

2 genetically identical daughter cells

Question 11

List the stages of the cell cycle:

Answer 11

1) Interphase

2) Mitotic (M)/Cell Division phase

Question 12

List the stages within Interphase:

Answer 12

G1,
S,
G2 phases

Question 13

Interphase

Answer 13

chromosomes present as chromatin

normal cellular metabolic activities occurring e.g. protein synthesis

Question 14

G1 Phase

Answer 14

growth, metabolism

centrosome replication begins

Note: in some cells that do not divide again once mature, (i.e. remain
in G1) – in these cells it is termed G0 phase

¦ e.g. nerve + some muscle cells

Question 15

S Phase

Answer 15

chromosomes replicate, but are still present as chromatin (not individually visible)

ALWAYS occurs before division (mitosis and meiosis)

kinetochore proteins are produced

Question 16

sister chromatids

Answer 16

replicates formed during S phase

Question 17

centromere

Answer 17

area of DNA where sister chromatids attach to one another

Question 18

kinetochore proteins

Answer 18

(produced during S phase) attach to each centromere to form the kinetochore

Question 19

kinetochore

Answer 19

protein + DNA complex,
1/chromatid meaning 1 on each side)

site of attachment of spindle microtubules

Question 20

G2 Phase

Answer 20

growth, metabolism

production of enzymes & other proteins needed for cell division

centrosome replication completed

Question 21

What does the Mitotic Phase involve?

Answer 21

a) mitosis

b) cytokinesis

Question 22

mitosis

Answer 22

= division of nuclear material (chromosomes)

4 phases, but continuous cycle!

i. Prophase
ii. Metaphase
iii. Anaphase
iv. Telophase

Question 23

cytokinesis

Answer 23

division of cytoplasm

Question 24

when mitotic phase ends:

Answer 24

mitosis & cytokinesis complete

daughter cells go into interphase (G1)

cycle starts over

Question 25

Prophase

Answer 25

``` chromosomes condense (thicken, coil) from chromatin form - become individually visible ``` nucleoli disappear and nuclear envelope breaks up centrosomes move to either pole ``` microtubules form spindle apparatus (starting at centrosomes) + attach to kinetochore proteins (called kinetochore microtubules) ``` Spindle moves chromosomes toward cell equator

Question 26

Metaphase

Answer 26

46 chromosomes line up on cell equator

Question 27

Anaphase

Answer 27

as the spindle microtubules shorten, the kinetochores are pulled away from each other – causing separation of centromeres, which results in separation of the chromatids 46 chromatids migrate to each pole cytokinesis (division of cytoplasm) begins

Question 28

Telophase

Answer 28

chromosomes uncoil to chromatin nucleoli, nuclear envelope reappear spindle disassembles cytokinesis completes (or may end after telophase ends)

Question 29

Meiosis

Answer 29

reproductive nuclear division

Question 30

meiosis produces

Answer 30

gametes (= ovum + sperm) 1 cell (diploid, 2n) produces 4 genetically dissimilar gametes (each haploid, n)

Question 31

What are the stages of Meiosis

Answer 31

involves: interphase (G1, S, G2) followed by 2 cell divisions: 1) Meiosis I, immediately followed by 2) Meiosis II between meiosis I + II = interkinesis NOT interphase (no DNA replication)

Question 32

Meiosis I

Answer 32

(reduction division = 2n to n) events same as in mitosis

Question 33

Prophase I

Answer 33

i. homologous chromosomes attach together = tetrads (4 chromatids in a row) ii. crossing over occurs • piece of 1 chromatid exchanges with matching piece from a chromatid of the homologous chromosome i.e. non-sister chromatid * acts to increase genetic diversity * e.g. you pass on your dad’s black hair with your mom’s blue eyes

Question 34

Metaphase I

Answer 34

23 tetrads line up along cell equator

Question 35

Anaphase I

Answer 35

tetrads (homologous chromosome pairs) separate and migrate to opposite poles i.e. 1 homologous chromosome (with 2 sister chromatids) goes to each pole chromatids DON’T separate

Question 36

Telophase I

Answer 36

same as mitosis telophase spindle disassembles nucleolus and nuclear envelope reappear chromosomes uncoil to chromatin

Question 37

After Meiosis I and cytokinesis:

Answer 37

each new cell has 23 different chromosomes (½ the number of Xms) = haploid (n) these cells DO NOT have homologous chromosomes chromosome 1 – 23 from Mom OR Dad (randomly segregated)

Question 38

Meiosis II

Answer 38

same as mitosis except with 23 chromosomes instead of 46 a) prophase II b) metaphase II - 23 chromosomes line up at equator c) anaphase II - 23 chromatids migrate to each pole d) telophase II ¦ cytokinesis – same for mitosis/meiosis (begins in anaphase/anaphase I/anaphase II, and continues through telophase/telophase I/telophase II)

Question 39

Where does meiosis take place in the body?

Answer 39

In the gonads ovaries= female testes= males

Question 40

Why meiosis?

Answer 40

Need to turn diploid germ cells into haploid gametes

Question 41

Fertilization

Answer 41

— spermatozoon (n) contacts and penetrates 2o oocyte (n) = fertilization — triggers completion of meiosis II in 2o oocyte – forms ovum (egg) — then ♂ + ♀ pronuclei unite — new cell = zygote (2n)

Question 42

pronucleus

Answer 42

nucleus of sperm/egg post-fertilization but prior to fusion