4 - The Cell Cycle, Mitosis, Meiosis

Question 1

What are the two cell types based on chromosome content? Where are they found? What is the difference?

Answer 1

Gametes and Somatic Cells.
Gametes only in the genitals.
Somatic cells are diploid, gametes are haploid.

Question 2

Define haploid and diploid.

Answer 2

Haploid (n): No homologous pairs

Diploid (2n): Homologous Pairs (2 codes for every gene)

Question 3

How many chromosomes are in a diploid cell? A haploid cell?

Answer 3

Diploid - 46 (2 pairs of 23)

Haploid - 23, unless in meiosis, then 46 (2 identical sets)

Question 4

Define homologous chromosomes

Answer 4

Chromosomes with same centromere position, length and genes, but different alleles.

Question 5

Define gene

Answer 5

A section of DNA coded for a particular trait (unit of heredity)

Question 6

Define alleles

Answer 6

Particular versions of genes for particular versions of a trait (blue vs brown eyes have different alleles in the eye colour gene)

Question 7

Define locus

Answer 7

The location of specific genes on a chromosome

Question 8

What are autosomes

Answer 8

Autosomal chromosomes (1-22) which code for somatic characteristics
Autosomal pairs are homologous but not identical

Question 9

Define sex chromosomes

Answer 9

23: code for sex determination

Sex chromosomes pairs are homologous in girls but not guys. (X&Y are different)

Question 10

What are the two stages of the cell cycle?

Answer 10

Interphase and mitosis or meiosis

Question 11

What are the characteristics of interphase?

Answer 11

 chromosomes present as chromatin

 normal cellular metabolic activities occurring e.g. protein synthesis

Question 12

What are the stages of interphase?

Answer 12

G1, S, G2

Question 13

Describe G1

Answer 13

 growth, metabolism

 at end of G1, centrosomes replicate

Question 14

What happens to cells that will not divide?

Answer 14

They enter G0 (permanent G1)

Question 15

Describe S phase

Answer 15

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

Question 16

What are sister chromatids?

Answer 16

Replicates of original chromosomes made in S phase.
 attached to each other at an area of DNA called the centromere
 kinetochore proteins (produced during S phase) attach to each centromere to form the kinetochore

Question 17

What is the kinetochore

Answer 17

protein + DNA complex, 1 per chromatid

site of attachment of spindle microtubules

Question 18

Describe G2

Answer 18

 growth, metabolism

 production of enzymes & other proteins needed for cell division

Question 19

What are the two parts of the mitotic phase of the cell cycle?

Answer 19

Mitosis

Cytokinesis

Question 20

What are the stages of mitosis?

Answer 20

P-MAT
Prophase
Metaphase
Anaphase
Telophase

Question 21

What is cytokinesis? When does it begin?

Answer 21

division of cytoplasm

begins during anaphase

Question 22

When is mitosis complete?

Answer 22

When cytokinesis is complete

 daughter cells go into interphase (G1)

Question 23

Describe Mitotic prophase

Answer 23

 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 24

Describe mitotic metaphase

Answer 24

 46 chromosomes line up on cell equator

Question 25

Describe mitotic anaphase

Answer 25

 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 26

Describe mitotic telophase

Answer 26

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

[reverse prophase]

Question 27

How many gametes are produces in mieotic division?

Answer 27

4

Question 28

What stage is in between meiosis I and II?

Answer 28

interkinesis

Question 29

What is the purpose of meiosis I?

Answer 29

Division of Homologous pairs.

Question 30

Describe meiosis I prophase

Answer 30

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

Question 31

Describe meiosis I metaphase

Answer 31

 23 tetrads line up along cell equator

Question 32

Describe meiosis I anaphase

Answer 32

 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 33

Describe meiosis I telophase

Answer 33

same as mitotic telophase

Question 34

Describe meiosis II

Answer 34

– 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

Question 35

What are germ cells? How are they formed?

Answer 35

Germ cells are the diploid cells that divide into gametes. They are formed by mitosis.

Question 36

What is the primary (1st degree) oocyte/spermocyte?

Answer 36

The 2n germ cell that will divide into 4 gametes.

Question 37

What is the secondary (2nd degree) oocyte/spermocyte?

Answer 37

The n intermediate cells formed by meiosis I that will each divide into 2 gametes.

Question 38

What is the ovum/spermatozoon?

Answer 38

The n gametes formed by meiosis II

Question 39

When does meiosis II occur in 2nd oocytes?

Answer 39

After fertilization

Question 40

Describe fertilization

Answer 40

 spermatozoon (n) contacts and penetrates 2nd oocyte (n) = fertilization
 triggers completion of meiosis II in 2nd oocyte – forms ovum (egg)
 then ♂ + ♀ pronuclei unite
 pronucleus = nucleus of sperm/egg post-fertilization but prior to fusion
 new cell = zygote (2n)