Mitosis & meiosis

Question 1

What are the 3 main stages of the cell cycle?

Answer 1

Growth/interphase, mitosis and cytokinesis (cytoplasmic division)

Question 2

What phases are there within the interphase?

Answer 2

G1 (growth 1)
S (synthesis)
G2 (growth 2)

Question 3

What happens in G1 phase?

Answer 3

Cellular contents (excluding chromosomes) are duplicated

Question 4

What happens in S phase?

Answer 4

Each of the 46 chromosomes are duplicated by the cell

Question 5

What happens in G2 phase?

Answer 5

The cell double checks the duplicated chromosomes for errors, and repairs any errors.

Question 6

What are the stages in mitosis?

Answer 6

PPMAT

Prophase
Prometaphase
Metaphase
Anaphase
Telophase

Question 7

What happens in prophase of mitosis?

Answer 7

Chromatin condenses into chromosomes
There are now chromosomes each made up of 2 sister chromatids

Centrosomes nucleate microtubules and move to opposite poles of the nucleus

Question 8

What happens in prometaphase?

Answer 8

Nuclear envelope breaks down

Microtubules invade nuclear space

Chromatids attach to microtubules

Question 9

What happens in metaphase?

Answer 9

Chromosomes line up at the equator of the cell

Question 10

What happens in anaphase?

Answer 10

Sister chromatids are separated and pushed to opposite poles of the cell

Question 11

What happens in Telophase?

Answer 11

Nuclear membranes reform

Chromosomes unfold into chromatin

Cytokinesis begins

Question 12

How would you recognise cells in prophase?

Answer 12

Cells have dark condensed chromosomes

Question 13

How would you recognise cells in metaphase?

Answer 13

Dark chromosomes line up along middle

Thick stripe in middle of cell

Question 14

How would you recognise cells in anaphase?

Answer 14

Chromosomes lined up in 2 lines at opposite poles of the cell

Two dark stripes either side of cell

Question 15

How would you recognise cells in Telophase?

Answer 15

Look to be about to divide

Question 16

What is mitosis?

Answer 16

Cell division that results in 2 daughter diploid cells each having the same number of chromosome (46) and genetically identical

Question 17

What is meiosis?

Answer 17

Cell division that results in 4 haploid cells being produced from 1 diploid one.

Happens in two sections:
Meiosis 1 & Meiosis 2

Question 18

Name the stages of meiosis in order?

Answer 18

MEIOSIS 1
Prophase 1
Metaphase 1
Anaphase 1
Telophase 1

MEIOSIS 2
Prophase 2
Metaphase 2
Anaphase 2
Telophase 2

Question 19

Which cells does meiosis occur in?

Answer 19

Gametes

Question 20

What happens in prophase 1 of meiosis?

Answer 20

Chromosomes pair and ‘crossing over’ occurs - recombinant chromosomes are formed

Question 21

What happens in prometaphase 1 of meiosis?

Answer 21

Spindle apparatus is formed and attaches to spindle fibres by kinetochores

Question 22

What happens in metaphase 1 of meiosis?

Answer 22

Homologous pairs of chromosomes are arranged as a double row along the equator

Arrangement along equator is random

Question 23

What happens in anaphase 1 of meiosis?

Answer 23

Homologous chromosomes are separated and move to opposite poles

So there are entire chromosomes at each pole

Question 24

What happens at Telophase 1?

Answer 24

Nuclear membrane reforms and cytokinesis begins to occur

Question 25

Meiosis ? separates pairs of homologous chromosomes?

Answer 25

I

Question 26

Meiosis ? separates each chromosome into two chromatids?

Answer 26

II

Question 27

What happens in prophase II of meiosis?

Answer 27

Chromosomes condense and nuclear membrane dissolves | Spindle fibres form

Question 28

What happens in metaphase II of meiosis?

Answer 28

Chromosomes line up along centre and spindle fibres attach to centromere

Question 29

What happens in anaphase II of meiosis?

Answer 29

Centromeres divide and sister chromatids move to opposite poles

Question 30

What happens in Telophase II of meiosis?

Answer 30

Chromosomes get to opposite ends of pole and nuclear membrane reforms

Question 31

Is meiosis I or meiosis II the same as mitosis?

Answer 31

Meiosis II

Question 32

Briefly describe sperm production (spermatogenesis).

Answer 32

Primordial germ cells > lots of mitoses > Spermatogonia Meiotic divisions begin at puberty Cytoplasm divides evenly After meiosis II there are 4 equal gametes Takes 60-65 days Millions of mature sperms continuously produced

Question 33

How many sperms per ejaculate?

Answer 33

100-200 million

Question 34

Briefly describe egg production (oogenesis).

Answer 34

Primordial germ cell > 30 mitoses > oogonia Oogonia enter prophase of meiosis I by 8th month of development (pre-birth) Process suspended until puberty Cells enter ovulation Cytoplasm divides unequally Meiosis II is only completed if fertilisation occurs

Question 35

What does Mendel's 2nd law state?

Answer 35

In the inheritance of more than one pair of traits in a cross simultaneously, the factor responsible for each pair of traits are distributed to the gametes.

Question 36

What is non-disjunction?

Answer 36

Failure of chromosomes to separate in meiosis I OR failure of sister chromatids to separate in meiosis II

Question 37

When does crossing over occur in meiosis?

Answer 37

Prophase I

Question 38

What's the difference between numerical and structural chromosomal abnormalities?

Answer 38

Numerical: Down's syndrome for example - failure at anaphase chromosomes are not split, 3 copies of chromosome 21 end up in one gamete Structural: Deletion, duplication or translocation of bases/genes