Mitosis And Meiosis

Question 1

List stages of the cell cycle.

Answer 1

Interphase- G0, G1, S and G2
Prophase
Prometaphase
Metaphase
Anaphase
Telophase
Cytokinesis

Question 2

What is an allele?

Answer 2

Different variations of the same gene.

Question 3

What do non-sister chromatids of homologous pairs have in common?

Answer 3

They carry the codes for the same genes, but the alleles may be different.

Question 4

If the alleles are the same on two chromatids of a replicated chromatids they are called?

Answer 4

Sister chromatids.

Question 5

What form are chromosomes in when drawn or seen in common Histological photos?

Answer 5

Replicated and condensed

Question 6

What is a homologous pair?

Answer 6

Two copies of the same chromosome in each cell, one chromosome carrying paternal genetic information and the other carrying maternal information. The genes coded for may be the same but the alleles are different.

Question 7

What stages of meiosis gives rise to genetic variation?

Answer 7

Random assortment of chromosomes in Metaphase 1 (line up paternal and maternal on different sided for each chromosome pair)
Crossing over in Prophase 1

Question 8

What is G0?

Answer 8

G0 is the cell exiting the cell cycle either temporarily or permanently.
Nerve cells don’t replicate so they exist in G0
Liver cells temporarily enter this stage.

Question 9

Do homologous pairs line up in mitosis?

Answer 9

No, that’s meiosis.
Mitosis all the chromosomes just line up randomly- no need for a partner because you want to just split the two chromatids from every chromosome- aim is identical cells.

Question 10

What’s the nucleolus?

Answer 10

5 chromosomes coding the genes for rRNA in the herterochromatin.

Question 11

How do homologous pairs find each other?

Answer 11

Sequences in each chromosome are similar at certain loci. It is this sequence recognition that lets them pair up.

Question 12

What is a centromere?

Answer 12

The part of the chromosome that holds sister chromatids together. The centromere consists of a sequence of base repeats.

Question 13

What is a telomere and why do we have them?

Answer 13

TTAGGG sequence repeats at the end of each chromatid to protect DNA from degradation. Replication shortens the telomere every time.

Question 14

What is the p arm of an acrocentric chromosome called?

Answer 14

Satellite

Question 15

The position of the centromere along with the size of the chromosome helps us identify and group them. Please name the 3 positions of centromere in humans.

Answer 15

Metacentric- middle
Submetacentric- just off the mid line
Acrocentric- way off centre, just a small piece on one side.

Telocentric at the telomeres doesn’t exist in humans

Question 16

What is mitosis?

Answer 16

Cell division for somatic cells to produce 2 identical daughter cells that match the DNA of the parent cell exactly.

Question 17

What kind of tissues require mitosis growth more regularly?

Answer 17

Cells that are frequently exposed to stress eg epidermal cells, mucosal cells
Cells that get used up to make things and would otherwise be used up in the process eg bone marrow and spermatagonia.

Question 18

Describe mitosis prophase.

Answer 18

Nuclear membrane break down
Chromosomes condense
Spindles form

Question 19

Describe mitosis Prometaphase

Answer 19

Spindle fibres attach to chromosomes

The chromosomes condense further

Question 20

Describe metaphase in Mitosis

Answer 20

Chromosomes line up on the midline- they are pulled by kinetochore so attached to the centrosomes at either pole of the cell.

Question 21

Describe Mitosis anaphase.

Answer 21

Sister chromatids separate and become individual unreplicated chromosomes.
The unreplicated chromosomes move to the poles, pulled by the kinetochores

Question 22

What happens in telophase of mitosis.

Answer 22

Nuclear membrane reforms
Spindles disappear
Chromosomes decondense

Question 23

What is cytokineses?

Answer 23

Cytoplasm division giving daughter cells

Question 24

How many chromosomes are in a cell?

Answer 24

23 homologous pairs so 46 individual chromosomes which may or may not be replicated depending on the stage of the cell cycle.

Question 25

In interphase the Chromosmes aren't condensed so do the fall apart and separate?

Answer 25

They still exist in chromosomal territories, but they aren't condensed like we normally visualise them. We visualise replicated chromosomes in their homologous pairs.

Question 26

What is a replicated chromosome in its homologous pair called?

Answer 26

Bivalend or Tetrad

Question 27

What is meiosis?

Answer 27

Special cell division for germ line cells that produce non identical haploid cells from diploid parents. It involves one lot of DNA replication and two lots of cell division to make 4 haploid cells.

Question 28

Describe prophase in meiosis 1

Answer 28

Nuclear membrane degrades Chromosome condense and find their homologous pair. Crossing over. Spindles form

Question 29

Describe Prometaphase in meiosis

Answer 29

Doesn't exist

Question 30

Describe metaphase 1 in meiosis

Answer 30

The homologous pairs line up on the cell midline. THIS IS THE ONLY TIME HOMOLOUS PAIRS LINE UP ANYWHERE IS ANY TIME OF CELL DIVISION.

Question 31

Which part of meiosis is responsible for haploid gametes?

Answer 31

Anaphase 1 where the HOMOLOGOUS pairs are separated not the sister chromatids. This results in 23 replicated chromosomes in each cell going into meiosis 2, not 46.

Question 32

Meiosis 2 is similar to mitosis- underline the key elements.

Answer 32

Prophase nuclear envelope breaks down and spindles form. metaphase the 23 Chromosmes line up in the midline (note not 46 like in mitosis) Anaphase splits up the sister chromatids to different poles of the cell. Telophase reforms the nuclear envelope before cytokinesis.

Question 33

How many centrosomes should there be in any cell?

Answer 33

2, to make a bipolar cell in division- moves the sister chromatids to and end each.

Question 34

What is a key difference between meiosis 1 and meiosis 2

Answer 34

Meiosis 1 metaphase means 23 homloous pairs line up and anaphase means the pairs get split up into different cells. Meiosis 2 metaphase lines up 23 chromosomes and anaphase separates sister chromatids

Question 35

Name 2 functions of meiosis

Answer 35

Conserve chromosome number from generation to generation. | Genetic diversity through random assortment in metaphase 1 and crossing over in prophase 1

Question 36

How long is spermatogenesis?

Answer 36

60days from spermatagonia to a mature sperm

Question 37

How long does oogenesis take and why is this a cause for concern in older mums?

Answer 37

12-50 years. | Meiosis only completes at fertilisation, that leaves chromosomes exposed for damage to their DNA for many years.

Question 38

What is misegregation of Chromosmes in meiosis?

Answer 38

When anaphase goes wrong, in either stage of meiosis. No dysjunction gives rise to Aneuploidy.

Question 39

What is mosaicism and what influences it?

Answer 39

More than one cell line in a organism or tissue. | The degree of mosaicism is influence by how far after the first zygotic division the change happens.

Question 40

What are mitosis spindles made from?

Answer 40

Micro tubules

Question 41

How do cancer treatments acting on the mitosis spindles help?

Answer 41

No spindles = no cell division= no tumour growth

Question 42

What is an oncogene?

Answer 42

Promoting cancer gene- we each have two one on each chromosome of the pair

Question 43

Where is Aneuploidy common?

Answer 43

Cancer

Question 44

How many tumour up pressing genes should you have?

Answer 44

2, one gene on each chromosome of the homlogous pair

Question 45

Mitosis errors in cancer can lead to:

Answer 45

Tumour heterogeneity Numerical chromosome instability Structural chromosomal instability

Question 46

What promotes numerical chromosomal instability?

Answer 46

More than two centrosomes in a cell- multipolar spindles

Question 47

How can we target centrosomes in cancer treatment?

Answer 47

It is common to have multiple centrosomes in cancer cell. These cells cluster at the two poles of the cell in mitosis which then results in viable cells. If the drug targets the clustering mechanism the daughter cells are likely to be less viable. This is a cancer cell specific treatment- centrosomes don't cluster in normal cells.