Lec 2 Mitosis and Meiosis

Question 1

What does mitosis produce?

Answer 1

two identical diploid daughter cells

Question 2

What does meiosis produce?

Answer 2

Gametes - sperm and egg cells
they are gentically diverse haploid cells
they have half the number of chromosones

Question 3

What is a somatic cell?

Answer 3

any non reproductive cell

Question 4

In what cases do we need mitotic growth?

Answer 4

some tissues, such as the epidermis, mucosae and bone marrow

Question 5

Describe the structure of a chromosome before mitosis

Answer 5

has a short p arm and a long q arm
a centromere
telomeres on each end
made up of a pair of sister chromatids

Question 6

What are the possible positions of a centomere

Answer 6

metacentric
submetacentric
acrocentric
telocentric

Question 7

What are the phases of mitosis

Answer 7

prophase, prometaphase, metaphase, anaphase, telophase

Followed by cytokenisis

Question 8

What are the phases of meiosis

Answer 8

prophase 1, metaphase 1, anaphase 1, telophase 1, cytokenisis
prophase 2, metaphase 2, anaphase 2, telophase 2, cytokenisis

Question 9

Describe the process of prophase in detail

Answer 9

Prophase - nuclear envelope breaks down
chromosones begin to condense
spindle fibres appear
centrioles begin to move to opposite ends of the cell
kinetocores recognise and bind to the centromeres

Question 10

Describe prometaphase in mitosis

Answer 10

chromosones begin to line up on the metaphase plate,
pulled by the kinetocore spindle fibres
the centrioles are now on opposite ends of the cell

Question 11

Describe Metaphase and anaphase

Answer 11

Metaphase - chromosomes are now lined up on the metaphase plate
spindles begin to pull the chromosomes apart
Anaphase - 2 daughter chromsomes are pulled to opposite ends of the cell, as centromeres divide

Question 12

Describe telophase and cytokenisis

Answer 12

Telophase- nucleus/nucleolus begin to reform
cleavage furrow forms as cleavage begins
they are now 2 identical copies
Cytokenisis- The cytoplasm divides

Question 13

what is a homologous chromosome pair?

Answer 13

they have the same DNA, and same genes, they may have different alleles

Question 14

sister chromatids have?

Answer 14

the same DNA and the same alleles

Question 15

Noo sister chromatids have?

Answer 15

The same DNA and potentially different alleles

Question 16

what is an allele

Answer 16

a variant of the same gene

Question 17

what does meiosis produce?

Answer 17

4 non identical haploid cells

Question 18

what is formed during prophase 1? why?

Answer 18

a tetrad(bivalent form) this allows crossover (at chiasma) to happen between non sister chromatids
the maternal and paternal DNA is swapped
this is known as recombination

Question 19

what happens during prophase 1?

Answer 19

same as in mitosis - go over this aswell
except tthe homologus pair locate each other to form a tetrad
they can do this as they have the same DNA
This allows recombination (crossing over) to happen

Question 20

what happens during metaphase 1 and anaphase 1?

Answer 20

metaphase 1 - the Homogulous pair lines up on the metaphase plate
Anaphase 1 - the tetrad separates in two. they are pulled to opposite end of the cell randomly

Question 21

describe telophase 1

Answer 21

same as in mitosis - explain
there are now 23 chromosomes in each cell.
2 daughter cells are produced

Question 22

what happens in meiosis 2?

Answer 22

both cells undergo prophase 2
then metaphase 2 where the chromosones line up randomly
sister chromatids are separated in anaphase 2
refomrs in telophase 2
this produces 4 non indentical haploid cells

Question 23

what is the purpose of meiosis ?

Answer 23

to maintain a constant number of chromosomes over generations
produces genetic diversity via the random chromosone assortment
and via the crossing over of non sister chromatids

Question 24

Describe Spermatogenisis

Answer 24

Check notes in book - same process as meiosis
can undergo mitosis to maintain sperm count
process takes about 60 days
prodiuces spermatids which mature to become sperm

Question 25

Describe Oogenisis

Answer 25

Check Using notes (write this up later)

Takes 12-50 years

Question 26

Bonus!

Answer 26

tip: crossing over is essential from meiosis to work

it will fail other wise and we dont know why

Question 27

Humans are bad at meiosis, what are the consequences of this?

Answer 27

30 in 100 fail,
this causes a third of all identified miscarriages
the leading cause of mental retardation
causes infertility

Question 28

What Error causes downs syndrome?

Answer 28

a non dis junction, where the chromatids fail to separate in anaphase. this causes aneuploidy (an abnormal chromosome number)

Question 29

How do we visualise and log chromosomes ?

Answer 29

We use a metaphase spread, this requires actively dividing cells, the spreads may look different depending on where the chromosomes were harvested from, and how long the process takes

Question 30

Karyotyping

what is a 47,xx, +21 ?

Answer 30

a female with trisomy ( Downs Syndrome), having one extra chromosome
Bouns : monosomy often terminates the cell line

Question 31

non disjunctions are also important in mitosis (particularly the first 50 miotic divisons)
what can a NDJ in mitosis cause?

Answer 31

a NDJ in the first post zygotic division will mean all cells are eg. 47,xy, +21, and hence all cells will have trisomy
this gives a non mosaic karyotype.
A NDJ after this will produce 47,+21/46, N
a mosaic karyotype

Question 32

What is Mosaicsm ?

Answer 32

the presence of two or more cell lines in an individual

can be body wide or tissue specific, this is dependent on when the NDJ occurs

Question 33

Explain Non Disjunctions is meiosis.

Answer 33

a NDJ in meiosis can happen in either stage 1 or 2. This causes different things.
In meiosis 1 a ndj will lead to one N+1 cell and one N-1 cell, which then divide to give two of each.
These are then fertilised by the sperm.
the potential products can be two Trisomy cells and two monosmy cells
If the NDJ happens in meiosis 2 then there are two normal cells, one with trisomy and one with monosomy.
So can get a healthy fetus.

Question 34

What do you know about the nucleolus?

Answer 34

a group of chromosomes gather, that are related to RNA coding and transcription and ribosome production.
it vanishes during M phase as the chromosomes condense into there individuals

Question 35

What is Stage G0?

Answer 35

when cells exit the cell cycle

they can do this permanently like neurons, or temporarily before a signal makes them re join

Question 36

how to chromosomes find each other in pro-phase 1 of meiosis?

Answer 36

Autosomes find each other as they have the same DNA sequence, allowing them to identify each other. Same Sequence Identity
Sex Chromosones although different, must have a similar sequnce to find each other. The PseudoAutosomalRegions are identical and hence the same process

Question 37

What are intersex people, how are they caused?

Answer 37

the SRY gene codes for initiation of male traits.
If crossing over occurs on sex chromosomes, and the SRY gene is swapped its possible to be a XY with no SRY gene and hence develop as a female
Or it is possible to be XX and have the SRY gene, so develop as a male who is XX

Question 38

just before/ after division what are the numbers you need to know for chromosones?

Answer 38

Before
46 chromosomes (23 Pairs), 92 Chromatids, 92 DNA molecules, 1 chromosome = 2 DNA Molecules
After
46 Chromosomes (23 Pairs), 46 Chromatids, 46 DNA molecules, 1 chromosome = 2 DNA Molecules