Meiosis Flashcards
0
Q
Diploid cell
A
- (2n)
- Cells contain 2 complete sets of each type of chromosome
- One set originated from the father and one from the mother
1
Q
Haploid cell
A
- (n)
- cells containing a single set of unpaired chromosomes
2
Q
Meiosis
A
- One diploid cell (2n) divides
- To form 4 haploid cells (n)
- chromosome number reduced to half
- Production of gametes (or gametophyte generation in plants)
3
Q
Alternation of generations
A
Alternation between diploid and haploid phases
4
Q
Stages of meiosis
A
Meiosis 1:
- Prophase 1;
- Metaphase 1;
- Anaphase 1;
- Telophase 1
Meiosis 2:
- Prophase 2;
- Metaphase 2;
- Anaphase 2;
- Telophase 2
5
Q
Homologous chromosomes
A
- Chromosomes containing the same gene sets
- Similar size, shape and information
- One paternal and the other maternal
6
Q
One duplicated chromosome at metaphase can be labelled with…
A
- Two sister chromatids
- joined together at the centromere
7
Q
DNA replication takes place during
A
Interphase (S-phase)
8
Q
Meiosis Prophase 1
A
- Nuclear membrane breaks down
- Chromosomes condense
- Bivalents form
- Crossing over occurs
- Centrioles produce spindle
9
Q
Meiosis Metaphase 1
A
- Homologous chromosomes align along equator
- Independent assortment of chromosomes
- Spindle fully formed
- Diagrams show evidence chiasmata
10
Q
Meiosis Anaphase 1
A
- Homologous chromosomes move to opposite poles
- Spindle threads contract pulling chromosomes
- Diagrams show evidence chiasmata
11
Q
Meiosis Telophase 1
A
- Each pole has haploid (n) chromosomes
- Nuclear membrane reforms
- Spindle disappears
- Cytokinesis usually visible
12
Q
Meiosis Prophase 2
A
- Nuclear membrane disappears
- Chromosomes condense
- Spindle apparatus forms
13
Q
Meiosis Metaphase 2
A
- Single chromosomes line up at equator
- Spindle fully formed
14
Q
Meiosis Anaphase 2
A
- Sister chromatids split at centromere into two chromosomes
- Spindle contracts pulling single copy chromosomes to opposite poles
15
Q
Meiosis Telophase 2
A
- Nuclear membranes reform
- Spindle disappears
- Cytokinesis occurs
- Four haploid daughter cells produced
16
Q
Purpose of meiosis
A
- In animals: production of gametes (n)
- In plants: production of spores/gametophyte generation (n)
17
Q
Gametogenesis and what it is called in males and females
A
- Production of gametes
- In males: spermatogenesis
- In females: oogenesis
18
Q
Alternation of generations
A
When organisms alternate between haploid (n) and diploid (2n) forms during their life cycles
19
Q
Groups that have an alternation of generations
A
- Protists
- Fungi
- Plants:
- Bryophytes
- Pteridophytes
- Gymnosperms and
- angiosperms
20
Q
The different life forms of mosses and ferns
A
- Gametophyte (n) produces gametes (n)
- Gametes fuse to form zygote (2n)
- Zygote grows into sporophyte (2n)
- Sporophyte undergoes meiosis to produce spores (n)
- Spores grow into gametophyte
21
Q
Ploidy
A
The chromosome number in an organism
22
Q
The importance of meiosis
A
- Chromosome number halved - to maintain ploidy when gametes fuse
- Cells produced after meiosis genetically unique - introduces and mixes up variation of genes in a species
23
Q
How variation is ensured in offspring through meiosis
A
- Random independent assortment of chromosomes and segregation
- Chiasma formation during crossing over
- Random gametes involved in fertilisation
24
Term used when a problem occurs during meiosis result in a new chromosome number
Aneuploidy (a-new-ploidy)
25
Nondisjunction of chromosomes
* When a chromosome pair(s) fails to separate during meiosis
* resulting in aneuploidy for the gametes formed
26
Polyploidy
* When cells have more than two complete sets of chromosomes.
* More common in plants.
27
Down's syndrome
* Person with a ploidy of 47
* Extra chromosome number 21
* Also called trisomy 21
28
Causes of Down's syndrome
* An extra chromosome 21
* Possibly greater risk from external factors e.g. Radiation
* Risk increases with maternal age
29
Medical conditions associated with Down's syndrome
* Developmental difficulties
* Hearing and vision defects
* Heart abnormalities
* Leukemia
* Thyroid disorders
* Dementia in later life
* Shorter lifespan
30
Similarities between mitosis and meiosis
* DNA replicates prior during interphase
* Nuclear membrane and nucleolus break down during prophase
* Spindle forms during prophase
* Chromosomes condense during prophase
* Chromosomes line up on equator during metaphase
* Spindle contracts during anaphase
* Cytokinesis follows both meiosis and mitosis
31
Different locations in mitosis vs meiosis
* Mitosis: all somatic cells and asexual reproduction
* Meiosis: reproductive organs (in humans: testes and ovaries)
32
Process differences between mitosis and meiosis
* Mitosis both haploid or diploid cells divide; meiosis only diploid
* Mitosis has one division of chromosomes; meiosis separation in meiosis 1 and division in meiosis 2
* Mitosis has no pairing of homologous chromosomes; meiosis pairing occurs
* Mitosis one nuclear division; meiosis has two
* Mitosis has only one cytokinesis event; meiosis has two
33
Differences in the cells produced between mitosis and meiosis
* Mitosis produces two cells; meiosis four
* Mitosis maintains chromosome number; meiosis halves it
* Mitosis daughter cells with same genes; meiosis with unique genes
* Mitosis daughter cells identical; meiosis unique
34
Functional differences between mitosis and meiosis
Mitosis:
* growth,
* repair and
* asexual reproduction
Meiosis:
* for gamete formation,
* to maintain chromosome number in life cycle
