52. MEIOSIS I Flashcards
1
Q
- How does Meiosis produce Haploid Cells from Diploid Cells?
A
- the production of gametes
- these are egg and sperm cells
- the chromosome number is reduced by a half
- each new cell has only 1 chromosome from each pair
of homologous chromosomes
2
Q
- What are the products of Meiosis?
A
- 4 haploid cells
- there is a pairing of homologous chromosomes
- this is followed by 2 consecutive Meiotic Divisions
- these divisions come from an initial diploid cell
3
Q
- What follows after the Chromosomes duplicate?
A
- two divisions follow:
- Meiosis I (Reductional Division)
- Meiosis II (Equational Division)
4
Q
- What is Meiosis I?
A
- the pairing and the separation of Homologous
Chromosomes - this results in 2 haploid daughter cells
- each of these cells have replicated chromosomes
- 2 chromatids per chromosome
5
Q
- What is Meiosis II?
A
- it is when the sister chromatids separate
- this results in 4 Haploid Daughter Cells
- each of these has unreplicated chromosomes
- there is 1 chromatid per chromosome
6
Q
- Why does Meiosis I result in 2 haploid daughter cells?
A
- the cells are haploid in terms of their chromosome
content - they have one chromosome from each pair of
homologs
THE DAUGHTER CELLS ARE DIPLOID (2n):
- in terms of DNA content (chromatids)
- these have replicated
- there are now 2 chromatids per chromosome
7
Q
- What can be said about the number of chromosomes in human cells after Meiosis I?
A
- human cells have 23 chromosomes
- each has 2 chromatids
- there are 46 chromatids in total (2n)
NUMBER OF CHROMOSOMES:
- n
- 23 in humans
NUMBER OF CHROMATIDS:
- 2n
- 46 in humans
- this is the DNA content
8
Q
- Why does Meiosis II result in four haploid daughter cells?
A
- the cells are haploid in terms of chromosome number
- the cells are haploid in terms of DNA content
- the cells are haploid in terms of Chromatid number
- each chromosome has only 1 chromatid each
NUMBER OF CHROMOSOMES:
- n
- 23 chromosomes in humans
NUMBER OF CHROMATIDS:
- n
- 23 in humans
- this is the DNA content
9
Q
- Which phase precedes Meiosis I?
A
- Interphase
10
Q
- What happens during Interphase?
A
- DNA replication
- the chromosomes duplicate to form sister chromatids
- the sister chromatids are genetically identical
- they have the same alleles and the same gene
sequence - they are joined at the centromere
11
Q
- What is a Centromere?
A
- the region of a chromosome to which the microtubules
of the spindle attach
12
Q
- What happens to the single Centrosome during Interphase?
A
- the centrosome replicates during Interphase
- this forms two centrosomes
- these replicate during the S-Phase
13
Q
- What 5 phases does the division in Meiosis I occur in?
A
- Prophase I
- Metaphase I
- Anaphase I
- Telophase I
- Cytokinesis
14
Q
- How long does Prophase I take?
A
- it takes 90% of the time required for Meiosis
15
Q
- What happens during Prophase I?
A
- the chromosomes begin to condense
- a synapsis happens
17
Q
- What happens after the Synapsis in Prophase I?
A
- each pair of chromosomes forms a tetrad
- a tetrad is a group of 4 chromosomes
- this is also known as a Synaptonemal Complex
19
Q
- What is Genetic Recombination (Crossing Over)?
A
- it is the exchange of DNA segments
- these are exchanged between non-sister chromatids of
Homologous Chromosomes - this may or may not occur during Prophase I in Meiosis I
- it is a random event
- it has an effect on variation if it does happen
