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MCBG > L9 - Mitosis And Meiosis > Flashcards

L9 - Mitosis And Meiosis Flashcards

1
Q

Outline the phases of the cell cycle

A

2 main phases:

  1. INTERPHASE
    - G1: cell grows
    - S(synthesis): DNA replication
    - G2: cell grows, protein synthesis
  2. M PHASE: mitosis phase
    - Mitosis and meosis
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2
Q

Outline the classic X-shape structure of chromosomes

A
  • 2 identical DNA molecules
  • 2 sister chromatids
  • telomeres: repeated sequences of TTAGGG at each end of chromosome/chromatid
  • centromere: regions of dna where sister chromatids tightly connected
  • p arm (small/petite) arm and q (tall) arm
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3
Q

A) How are chromosomes grouped?

B) what group are the X and Y chromosomes in?

A

A) - according to size and shape
- A-G

B) x is in C and Y is in G

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4
Q

Haploid vs Diploid?

A

Diploid: 2 chromosome sets (2n)

  • in diploid somatic cells there is 46 chromosomes in each
  • copies of each chromosome

Haploid: 1 copy of each chromosome

  • in haploid somatic cells there is 23 chromosomes in each
  • single chromosome set (n)
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5
Q 
A) What is Mitosis? 
B) What cells is it for?
C) what stage in the cell cycle is just before mitosis? 
D) stages of mitosis
E) purpose of mitosis?
A

A) cell division in which 1 cell (mother) divides to produce 2 new (daughter) cells that are genetically identical to itself

B) somatic cells

C) G2- just had DNA replication

D) 1. Prophase 2. Prometaphase 3. Metaphase 4. Anaphase 5. Telophase

E) asexual reproduction, growth and repair

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6
Q

Mnemonic to remember stages of Mitosis

A 
Please Pee (on the) MAT
P: prophase 
P: prometaphase 
M: metaphase
A: anaphase
T: telophase
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7
Q

Outline the stages of mitosis and what happens in each

A
  1. PROPHASE:
    - spindle fibres form
    - nucleolus breaks down
    - chromosomes condense (visible)
  2. PROMETAPHASE:
    - nuclear envelope breaks down
    - spindle fibres attach to chromosomes
    - kinetochores (protein that bind to centromere)
  3. METAPHASE
    - chromosomes align at metaphase plate
    - 2 kinetochores of each chromosome should be attached to microtubules from opposite spindle poles
  4. ANAPHASE
    - sister chromatids separate and pulled to opposite ends
    - the protein glue that holds them together is broken and each is now its own chromosome
  5. TELOPHASE:
    - nuclear membrane reforms
    - chromosomes decondense
    - spindle fibres disappears
    - nucleolus reappears

CYTOKINESIS OCCURS: division of cytoplasm to form 2 new cells

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8
Q

Define:
A) Homologous chromosomes
B) Sister chromatids
C) non-sister chromatids

A

A) pair of chromosomes (one from each parent) that are similar in length, gene position and centromere location but genes contain different alleles

B) 2 chromatids of a replicated chromosome connected by a centromere, have same alleles at same loci, formed in S phase

C) 2 chromatids formed from 2 diff homologous chromosomes, contain diff alllels of same genes at same loci, formed in MI of meiosis

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9
Q

A) What cells is meiosis for?
B) what does meosis produce?
C) purpose meiosis?
D) Phases of meiosis

A

A) germ line cells
B) 4 non identical cells with half the chromosome content of parent cells (produces 4 haploid cells (n))
C) production of eggs and sperm —> sexual reproduction
E) MEIOSIS I: Prophase I, Metaphase I, Anaphase I, Telophase I
MEOISIS II: Prophase II, METAPHASE II, ANAPHASE II, TELOPHASE II

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10
Q

Outline the steps of Meiosis (different to mitosis)

A

PROPHASE I:

  • homologous chromosomes pair
  • crossing over occurs (exchange of genetic material) point of crossing over = chiasmata
  • bivalve then: 2 HC having at least one dna cross over
  • crossing over is RANDM

METAPHASE I:

  • Homologous pairs (not individual chromosomes) line up at metaphase plate
  • random assortment of Homolgous pairs

ANAPHASE I:

  • homolgous chromsmes in each bivalent are seperated and move towards opposite poles of the cell
  • sister chromatids DO NOT COME APART

TELOPHASE I:

  • chromosomes arrive at opposite poles
  • 2 haploid daughter cells

PROPHASE II:

  • basically like mitosis
  • chromosomes condense, nuclear envelope breaks down

METAPHASE II:
- chromosomes line up at metaphase plate

ANAPHASE II:
- sister chromatids sepereate and pulled to opposite poles

TELOPHASE II:

  • nuclear membranes form around each set of chromosomes
  • chromosomes decondense

Cytokinesis splits chromosomes sets into new cells

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11
Q

What is the final product of meiosis?

A

4 haploid cells in which each chromosome has just one chromatid

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12
Q

How does meiosis produce genetic variation?

A
  1. Crossing over of HC: exchange of genetic material, the points are random and the number of crossing over points is also renadom —> PROPHASE I
  2. Random assortment/ orientation of homolgous pairs at metaphase plate during metaphase I allows for production of gametes with many different assortments of homolgous chromosomes
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13
Q

Similarities and differences between A) mitosis and B) meiosis

A

Number of divisions:
A) 1 B) 2

Number of chromosomes in parent
A) diploid number (2n) 46 in humans B) diploid number (2n) 46 in humans

Number of chromosomes per daughter cell at end
A) diploid numbe (2n) 46 in humans b) haploid number (n) 23 in humans

Location of process
A) somatic cells B) reproductive organs

Type of reproduction
A) Asexual B) sexual

Genetic variation
A) none B) some- crossing over and random assortment at metaphase plate

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14
Q

a) what is spermatogenesis?
B) What are the stages and what do they produce
C) length of spermatogenesis?

A

A) cell division to produce male gametes
B) Begins with a spermatogonium (immature cells) that undergo mitosis to duplicate and form primary spermatocytes. Primary spermatocytes undergo Meiosis I to produce secondary spermatocytes then meiosis II to produce spermatids. Spermatids then undergo spermiogenesis to mature into 4 spermatozoas (sperms)
c) about 60 days

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15
Q

A) What is oogenesis
B) What are the stages and what do they produce
C) length?

A

A) meiosis cell division to produce female gametes
B) Begins with an oogonium which under goes mitosis to duplicate and produces primary oocyte, undergoes meiosis I to form one polar body and one secondary oocyte. Both undergo meiosis II to form 3 polar bodies and 1 mature ovum
C) 12-50 years!!

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16
Q

How many a) chromosomes b) DNA molecules and C) chromatids does a human cell contain:

i) at the end of G1
ii) in G1 just after mitosis?
iii) Just before meiosis I?

A

i) Hasn’t gone through DNA replication yet:
a) 46 chromosomes b) 46 DNA molecules and c) 46 chromatids

ii) Chromatids were separated at the poles and hence
a) 46 chromosomes that have 1 DNA molecule b) 46 c) 46

iii) About to undergo meiosis I and hence DNA has been replicated
a) 46 chromosomes b) 92 DNA molecules

17
Q

What happens to a) the amt of DNA and b) the amt of chromosomes after S phase?

A

a) amt of DNA is doubled

b) same amt of chromosomes

18
Q

If you are told that in a cell division of human cells 23 unduplicated structures are seen to travel to each pole, can you tell whether the cell is mitosis or meiosis?

A

Yes you can it is MEIOSIS II:

  • During ANAPHASE of Mitosis: 46 unduplicated chromatids travel to each pole
  • during ANAPHASE of Meiosis I: 23 duplicated structures go to each pole
  • during ANAPHASE II of meiosis II: 23 unduplicated structures go to each pole
19
Q

During mitosis the nucleolus disappears during prophase:

a) what is the nucleolus
b) why is it that the nucleolus is present in the nucleus during interphase but is absent most of mitosis?

A

a) Structure of 5 different chromosomes where rRNA genes are expressed and is heavily stained
b) during mitosis the chromosomes condense and hence these 5 chromosomes will condense into individual chromosomes, separatingf and hence the nucleolus will no longer be visible

20
Q

At what point during Meiosis do the cells become haploid and why?

A

After meiosis I:

At the start of Meiosis the cell is diploid, it has 46 chromosomes in it (with 92 chromatids/DNA molecules).
- during Anaphase I, the homologous pairs seperate and go to opp poles and cytokinesis happens and so now each new cell has only 23 chromosomes in it which is HALF the original number in the original cell making it haploid

21
Q

In a real human cell:

a) how many chromosomes are there before MEIOSIS and how many DNA molecules and what is the chromosome no?
b) how many chromosomes would line up at the metaphase I plate
c) how many chromosomes would be in a cell that has just gone through MEIOSIS I and how many DNA molecules? What is the chromosome no?
d) How many chromosomes would be in a cell that has just gone through MEIOSIS II and how many DNA molecules? What is the chromosome no?

Think about the shapes of the chromosomes

A

a) 46 chromosomes in pairs, 92 DNA molecules. DIPLOID
b) 23 pairs –> 46
c) There are 23 chromosomes in a cell that has just undergone meiosis I, 46 DNA molecules. It is HAPLOID.
would be the X shaped chromosomes
d) There are still 23 chromosomes in a cell but now there is 23 DNA molecules as well. still haploid.
Would be the stick shaped chromosomes

22
Q

a) What is karyotyping?
b) What is the standard format to describe the karyotype?
c) What would the karyotypes be for the following:
i) normal female
ii) normal male
iii) male with trisomy 21

A

a) The process of pairing and ordering all the chromosomes of an organism, thus providing a genome-wide snapshot of an individual’s chromosomes
b) Chromosome no, sex complement and any structural changes
c)
i) 46, XX
ii), 46, XY
iii) 48, XY + 21

23
Q

a) What is aneuploidy?

b) What are the types

A

a) abnormal number of chromosomes
b) Trisomy (2n +1): addition of one chromosome to one pair in diploid set
Monosomy: is when an organism has only one copy of a chromosome that should be present in two copies (2n−1)

24
Q

What is mosaicism?

A

The presence of two or more cell lines in an individual

25
Q

a) What is nondisjunction?

b) What does it cause

A

a) Occurs when pairs of Homologous chromosomes OR sister chromatids fail to seperate during cell division- can occur during Mitosis and meiosis
b) Aneuploidy

26
Q

Outline the effects of nondisjunction in mitosis

A
  • Can lead to two degrees of mosaicism depending on which point of division non-disjunction occurs at
  1. if it occurs during FIRST post-zygotic division: LEADS TO NON-MOSAIC KARYOTYPE
    - A 2n cell will undergo mitosis and instead of producing 2, 2n identical cells, one cell will be 2n+1 (trisomy will occur) and 1 will be 2n-1 (monosomy will occur but this cell line normally lost)
    - every cell that undergoes a successful mitotic division from here on will be 2n+1 –> non-mosaic karyotype
  2. If it occurs during later cell division (i.e. first division went normal) LEADS TO MOSAIC KARYOTYPE
    - some cells will be normal and some will be 2n+1 (trisomy) and some will be 2n-1 (monosomy) (most monosomy cell lines are lost)
    - hence the karyotypes are different –> mosaic karyotype
27
Q

Normally a monosomy cell line is usually lost. When can monosomy be tolerated?

A

Turner syndrome – People with Turner syndrome typically have one X chromosome instead of the usual two sex chromosomes.

28
Q

Outline the effects of nondisjunction in a) Meiosis I and b) Meiosis II

A

a) MEIOSIS I: during anaphase I
- at least one pair of homologous chromosomes did not separate.
- The end result is two cells that have an extra copy of one chromosome and two cells that are missing that chromosome.
- 2 cells have n+1 and 2 cells have n-1

b) MEIOSIS II: during anaphase II
- at least one pair of sister chromatids did not separate.
- two cells will have the normal haploid number of chromosomes. Additionally, one cell will have an extra chromosome (n + 1) and one will be missing a chromosome (n - 1).

29
Q

a) What is the SRY gene and what does it do?

A

a) provides instructions for making a protein called the sex determining region Y protein. It is involved in male sexual development

30
Q

What is the difference between non-disjunction and anaphase lag?

A

Non-disjunction: failure of chromosomal separation in anaphase of either meiosis or mitosis

Anaphase lag: delayed movement of a chromosome or chromatid during anaphase resulting in loss of the genetic material from inclusion into either daughter nucleus

MCBG (16 decks)

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