1
Q
Why do cells need to reproduce
2
A
- allow organisms to grow
- replace old, dead or damaged cells
2
Q
Name events of cell cycle
A
- G1 phase
- S phase
- G2 phase
- M phase
3
Q
G1 phase
4
first growth phase
A
- cells produce proteins
- carry out normal tasks
- ends with DNA beginning to replicate
- duplication of organelles
4
Q
S phase
1
synthesis phase
A
DNA molecules in cells form exact copies of themselves
5
Q
G2 phase
2
second growth phase
A
- relatively short
- involves prep for cell division
6
Q
M phase
1
mitotic phase
A
- cell divides into two daughter cells
7
Q
What happens after division for cells in cell cycle
2
A
- some re-enter G1 phase
- some stop dividing but still function (G0 phase)
8
Q
Why is it vital that daughter cells get the exact same DNA as their parent cell?
1
A
- as DNA controls the structure and actions of cells
9
Q
Mitosis definition
A
process of division of nuclei of a cell in which the two daughter cells have identical sets of genetic material as the parent nucleus
10
Q
Interphase
2
A
- period between nuclear divisions (mitosis)
- includes G1, S and G2 phase
- quantity of DNA in nucleus doubles (bc of S phase)
11
Q
Haploid number
A
23 chromosomes = n
12
Q
Diploid number
A
46 chromosomes = 2n
13
Q
Early prophase
4
A
- 2 pairs of centrioles become visible and move to opposite poles of cells
- microtubules begin to radiate from centrioles to form spindle fibre framework
- nucleolus disappears, nuclear membrane begins to break down
- duplicated threads of chromatin tightly coil to become visible as chromosomes
14
Q
Late prophase
4
A
- centrioles have reached opposite poles of cell
- microtubules have joined to form framework of fibres (spindle)
- nuclear membrane completely broken down
- chromatid pairs migrate to equator of cell
15
Q
Metaphase
2
A
- chromatid** pairs line up** on equator of spindle
- centromere attaches to spindle fibre
16
Q
Anaphase
3
A
- chromatids seperate at centromere
- pull away from each other to opposite poles by spindle fibres
- centromeres still attached to spindle
17
Q
Telophase
6
A
- 2 sets of chromosomes form tight groups at each pole of cell
- nuclear membrane forms around each group
- nucleolus appears
- spindle fibres disappear
- centrioles divide
- chromosomes gradually uncoil to go back to chromatin threads
18
Q
Why does chromatin coil to form chromosomes
A
to make distribution of DNA easier
19
Q
Cytokinesis
5
A
division of cytoplasm to form two new cells
- at the end of telophase
- cell membrane moves inwards creating a furrow between 2 nuclei
- furrow gradually deepens until it cuts cytoplasm in 2, each with own nucleus
- cell membrane reforms around each new cells
20
Q
Meiosis
2
A
special process of nuclear division resulting in production of sperm/ova
resulting in 4 haploid daughter cells from 2 nuclear divisions
21
Q
Why are gametes haploid cells
A
so the zygote can recieve 23 chromosomes from each parent, so they can have 46 chromosomes not 92
22
Q
Homologous chromosomes
3
A
- exist in pairs
- identical in shape
- carry genetic info that influences same characteristics
23
Q
Where does meiosistake place
A
in the sex organs (gonads)
cells from ovaries/testes replicate to form gametes since gametes themselves can’t replicate
24
Q
Name the phases of meisos
A
- Interphase
- Prophase I, Metaphase I, Anaphase I, Telophase I
- Prophase II, Metaphase II, Anaphase II, Telophase II
25
Why doesn't the cell go back into interphase between Meiosis I and Meiosis II
as DNA doesn't need to be replicated again
26
Prophase I
| 5
- *chromatin condenses into chromosomes*
- chromosomes migrate to equator and **find homologous pair**
- *nucleolus disappears, nuclear membrane breaks down*
- *centrioles become visible and move to poles and spindle fibres form*
- **crossing over occurs**
27
Metaphase I
| 2
- chromosomes line up at equator **with homologous pair**
- *attach to spindle fibres by centromeres*
28
Anaphase I
| 2
- spindle fibres retract
- centromeres don't divide -> **one member of homologous pair moves to each pole**
29
Telophase I
| 5
- chromosomes uncoil to chromatin
- nuclear membrane reforms
- spindle disappears
- cytokenesis
- **results with 2 daughter cells each having 23 chromosomes, 46 chromatids**
30
Prophase II
| 2
- new spindle forms at right angles to original spindle direction
- *chromosomes move toward equator*
31
Metaphase II
| 1
chromosomes line up on equator in a single line
32
Anaphase II
| 2
- centromeres divide, seperating chromatids
- chromosomes move to opposite poles
33
Telophase II
| 3
- nuclear membrane forms
- cytokenesis
- **produces 4 haploid daughter cells with 23 chromosomes, 23 chromatids**
34
Differences between mitosis and meiosis
| disco pug
- **division** no.
- **independent** assortment
- ***synapsis** (whether homologous chromosomes line up and form **bivalents**)*
- **crossing** over
- **outcome** (no. cells)
- **ploidy** (diploid vs haploid)
- **use** (body cells or gametes)
- **genetics** (identical cells vs variation)
35
Three factors affecting variation
- crossing over
- non-disjunction
- random assortment
36
Crossing over
| 3
- during **prophase I**
- homologous chromosomes undergo process called **synapsis**, forming a **bivalent**
- then they may **cross break and exchange segments**, resulting in a **recombination**
37
Synapsis
fusion of chromosome pairs
38
Bivalent
pair of homologous chromosomes
39
Chiasma
*chiasmata plural*
point where 2 chromatids cross
40
Recombination
changing combination of alleles
41
Non-disjunction
| 2
**where one or more chromosomes fail to seperate during meiosis**
*results in gametes with one extra chromosome or one missing*
42
What happens if non-disjunction occurs during Anaphase I
4 daughter cells affected
2 extra, 2 less
43
What happens if non-disjunction occurs during Anaphase II
2 daughter cells affected
1 extra, 1 less, 2 normal
44
What does non-disjunction usually result in
| 2
- severe and distinctive birth defects
- often early miscarriages
45
Trisomy
condition where individual inherits an **extra copy of each chromosome**
*(3 instead of 2)*
46
Trisomy 21
| 3 symptoms, 2 points
extra copy of chromosome 21
- characteristic facial appearance
- variable degrees of intellectual disability
- physical abnormalities
*common in children of older mothers*
| Down Syndrome
47
Trisomy 13
| 5 symptoms
- intellectual disability
- small head
- extra fingers/toes
- cleft palate/lip
- malformation of eyes and ears
| Pateau Syndrome
48
Trisomy 18
| 2 symptoms
- intellectual disability
- defects in ears, eyes, hand and head
| Edward's Syndrome (think Edward is 18)
49
Monosomy
| 2
**individual is missing a chromosome**
*only have one copy, not two*
50
Partial monosomy
| 2
part of a chromosome is missing
*part of it has 2 copies, part has only 1*
51
Partial trisomy
| 2
part of extra chromosome attaches to one of the other chromosomes
*can result in many Down Syndrome symptoms*
52
Random/Independent Assortment
| 3
- **the random combination of alleles due to alleles seperating independently of each other**
- *orientation of pairs is random, assortment of chromosomes into gametes is also random*
- *the way one pair seperates is unaffected to the way other pairs seperate*
53
How to calculate number of gamete combinations
2^n
Human Bio - Unit 2
flashcards
Decks in class (16)
# Cards
-
Cell Division53
-
Male Reproductive System32
-
Cancer22
-
Female Reproductive System63
-
STI's48
-
Fertilisation11
-
Contraception47
-
ART's31
-
Development - Embryonic, Placental & Foetal55
-
Cell Differentiation13
-
Labour38
-
DNA36
-
Diagnosis of Foetal Health19
-
Protein Synthesis30
-
Epigenetics & Gene Imprinting24
-
Genetics & Inheritance30
