Cell Division Flashcards
What are the phases of the cell cycle?
G1 (First Gap) -> S (Replication of DNA) -> G2 (Second Gap) -> M Phase (Mitosis)
What is interphase of the cell?
G1, S and G2 Phases
What happens in the G1 Phase?
Cell is metabolically active and continuously grows
What happens in the S Phase?
DNA replication takes place -> each chromosome forms two sister chromatids connected at the centomere
- DNA content doubled, twice as many chromatids as chromosomes in G1 phase
Describe the mechanism of DNA replication
Semiconservative mechanism -> DNA molecules with 1 parental strand and 1 daughter strand (from environment)
What happens in the G2 Phase?
Cell growth continues and proteins are synthesised in preparation for M phase
What are chromosomes and sister chromatids?
Chromosome -> Discrete unit of genetic material
Sister chromatid -> Copies of DNA produced after DNA replication
What are the phases of mitosis?
Prophase -> Metaphase -> Anaphase -> Telephase (PMAT)
Describe the prophase of mitosis
- Chromatin fibres condense to form metaphase chromosomes
- Mitotic spindle starts to form
- Nuclear envelope completely disintegrates
What are kinetochore microtubules?
Binding of the microtubules of the mitotic spindle to the kinetochore protein located at the centromere of chromosomes
Describe the metaphase stage of mitosis
- Metaphase chromosomes align themselves in a single file along metaphase plate
- Kinetochore microtubules attach to kinetochore at centromeres of chromosomes
Describe the anaphase stage of mitosis
- Kinetochore microtubules shorten
- Sister chromatids seperate
- Non-kinetochore microtubules lengthen to elongate the cell
Describe the telophase stage of mitosis
- Daughter chromosomes decondense
- Nuclear envelope reforms
Describe the cytokinesis process
!Occurs during telophase!
- Formation of cleavage furrow -> constricts to seperate cells (Animal)
- Vesicles from golgi apparatus move along microtubules to the center of the cell -> coalesce to form cell plate (Plants)
Role of Mitosis
- Enables growth in multicellular organisms
- Repair of worn-out or damaged tissues in the body
- Allows for unicellular organims to reproduce asexually
- Produces genetically identical cells
What are homologous chromosomes?
- Chromosomes that are the same size, centromere location and banding pattern
- Same genes are located at same position, however alleles may differ
What are haploids, diploids and polyploids?
- Diploid cells carry 2 sets of chromosomes -> humans cells are diploid
- Haploid cells contain one set of chromosomes -> gametes eg. egg and sperm
- Polyploids contain three or more chromosomes
What are the phases of Meiosis?
Stage 1: Prophase I -> Metaphase I -> Anaphase I -> Telephase I (Involves bivalents of homologous chromosomes)
Stage 2: Prophase II -> Metaphase II -> Anaphase II -> Telephase II (Involves chromomes with two sister chromatids)
Describe Prophase I of meiosis
- Homologous pairs undergo synapsis with each other to form a bivalent (verb: synapse)
- Crossing over occurs between non-sister chromatids -> occurs at the chiasma
- Nuclear envelope disintegrates
Describe Metaphase I of Meiosis
- Bivalents become attached to kinetochore microtubules
- Independent assortment occurs as bivalents randomly align along the metaphase plate
Describe Anaphase I of Meiosis
Kinetochore microtubules shorten, bivalents seperate to homologous chromosomes
Describe Telophase I & Cytokinesis of Meiosis
- Homologous chromosomes decondense
- Nuclear envelopes reform
- Cleavage furrow forms to seperate cell into two daughter cells
What does Meiosis I produce?
Two diploid daughter cells containing homologous chromosomes
How are Meiosis II and Mitosis similar and different?
- Process of chromosomes seperating into sister chromatids is similar
- Four stages of Prophase, Metaphase, Anaphase and Telophase are basically identical
- Meiosis II produces 4 genetically different haploid gametes
- Mitosis produces genetically identical cell with same DNA content as parent cell
How does Meiosis promote genetic variation?
- Crossing Over in Prophase I
- Independent Assortment in Metaphase I
- Random fertilisation (only during fertilisation process)
How does crossing over promote genetic variation?
- Results in sister chromatids becoming non identical
- Produces new combinations of alleles not present in parents
- Results in gametes with a combination of various traits
How does independent assortment promote genetic variation?
- Bivalents line up randomly along metaphase plate and seperate
- Each daughter cell receives a different combination of maternal and paternal
What is nondisjunction?
- Homologous chromosomes in Meiosis I or Sister chromatids in Meiosis II fail to seperate
What is an allele?
The specific variant of a heritable feature that varies among individuals eg. black wing allele, speckled wing allele
