Week 11 - Reproduction: meiosis Flashcards
Understand the basic concept of sexual reproduction and the role of meiosis in sexual life cycles Describe how homologous chromosomes pair during meiosis Explain why meiosis I is called the reductive division. Describe the characteristic phases of meiosis Contrast the end products and significance of mitotic & meiotic cell division
1
Q
Meiosis
A
Producing haploid cells
2
Q
Fertilisation
A
- Haploid cells producing diploid cells.
- Union of gametes (sperm and egg)
3
Q
Gametes
A
- Sex cells in animals (sperm and eggs), arise from germ cells.
- Only cells in the human body produce by meiosis
4
Q
Zygote
A
- a fertilised set and has one set of chromosomes from
each parent. - produces SOMATIC CELLS by mitosis and develops into an adult
5
Q
Diploid cells
A
Somatic (non reproductive) cells of adults have 2 sets of chromosomes
6
Q
Haploid cells
A
Gametes (eggs and sperm) - only 1 set of chromosomes
7
Q
Karyotype
A
Particular array of chromosomes in an organism arranged according to size, staining properties and location of centrometre
Human cell - 23 pairs
→XX= female, XY=male
8
Q
Prophase I
A
- Chromosomes coil tighter and become visible, nuclear envelope disappears, spindle forms
- Each chromosomes has 2 sister chromatids
9
Q
Features of Meiosis - Synapsis
A
- During early prophase I
- Homologous chromosomes become closely associated or ‘become paired’
- Include formation of synaptonemal complexes → formation of tetrad or bivalents
→meiosis specific from of cohesion
10
Q
Crossing over
A
- Genetic RECOMBINATION between nonsister chromatids
- Allows homologues to exchange chromosomal material
- Alleles of genes that were formerly on separate homologues can be found on smae homologue
- CHIASMATA: site of crossing over → contact maintained until anaphase I
11
Q
Prophase I - continued
A
Synapsis
- homologues become closely associated
- crossing over occurs
- remain attached at chiasmata
12
Q
Metaphase I
A
Terminal chiasmata hold homologues together following crossing over
- microtubules from opposite poles attach to each homologue → not each sister chromatid
- HOMOLOGUES ARE ALIGNED AT THE METAPHASE PLATE SIDE BY SIDE
- Orientaiton of each pair of homologues on spindle is RANDOM
13
Q
Anaphase I
A
- microtubules of spindle shorten → chiasmata break
- HOMOLOGUES ARE SEPARATED FROM EACH OTHER AND MOVE TO OPPOSITE POLES → sister chromatids remain attached to eachother at their centromeres
- each pole has a complete haploid set of chromosomes consisting of one member of each homologous pair
- independent assortment of maternal & paternal chromosomes
14
Q
Telophase I
A
- NUCLEAR ENVELOPE RE-FORMS AROUND EACH DAUGHTER NUCLEUS
- sister chromatids are no longer identical because of crossing over (Prophase I)
- Cytokinesis may or may not occur
- Meiosis II occurs after an interval of variable length
15
Q
Meiosis I summary
A
REDUCTION DIVISION
- results in daughter cells that contain only one set of originial homologous pairs
- each chromosome in a daughter cell is derived from just one parent.
- Resuting cells retain both sister chromatids, so they are still diploids
- no DNA replication occurs before going into meiosis II
- Meiosis II will separate sister chromatids
