Meiosis Flashcards
what are two types of cell division in eukaryotic cells?
- mitosis
2. meiosis
what happens during meiosis? what kinds of organisms does this occur in? what is the function?
A diploid cell divides to produce 4 genetically unique
haploid cells
-Occurs in sexually reproducing organisms only
-to reduce the chromosome number by
half so when gametes fuse during fertilization a
diploid zygote is formed
what does meiosis do to the chromosome number? what kind of cells does meiosis occur in? what does meiosis produce in animals?
reduce by half
- therefore can only occur in diploid cells
- produces haploid gametes in animals (eggs/sperms)
what does a cycle of meiosis consist of?
- one cycle of DNA replication (interphase)
- 2 cycles of cell division (meiosis I and II)
what happens during meiosis I?
Homologous chromosomes separate
what happens during meiosis II?
Sister chromatids separate
when does interphase occur? what is the function? what are the sub-phases of interphase?
before meiosis I
- cell growth and DNA synthesis
1. G-1 –> growth again
2. S-phase –> chromosomes replicated
3. G-2 –> growth again
what are the 4 sub-phases of meiosis I?
- prophase I
2 metaphase I - anaphase I
- telophase I
Prophase I: what happens?
- chromosomes condense
- homologous chromosomes pair - synapsis
- Non-sister chromatids crossover –> Genetic information is exchanged between homologous chromosomes
- meiotic spindle forms
- centrosomes duplicate and move apart
Metaphase I: what happens?
-Paired homologous chromosomes line-up on metaphase plate
-Homologous chromosomes attached to opposite poles
of the spindle by microtubules
what is special about the chromatids after prophase I?
All 4 chromatids are unique blends of homologs from both parents
Anaphase I: what happens?
what happens to sister chromatids?
-Homologous chromosomes separate and move
towards opposite poles
-Sister chromatids remain attached at centromere
telophase I: what happens?
- the Cell divides (cytokinesis) –> Two haploid cells are formed
- nuclei reforms, nuclear envelopes reform, nucleoli reappear
- chromatids may or may not uncondense
what do each of the daughter cells contain after telophase I? what are these composed of? what kind of cells are these?
- Each half of the cell has one complete set of chromosomes
- Each chromosome composed of a pair of sister chromatids
- cells are haploid
what happens between meiosis I and II?
no DNA replication
what happens during prophase II?
meiotic spindle reforms
- Dna condenses
- Centrosomes duplicate move apart
what happens during metaphase II? where are chromatids attched?
- Chromosomes line-up on metaphase plate
- sister chromatids are attached to mcirotubules attached to opposite poles
what happnes during anaphase II?
- Sister chromatids separate
- Chromosomes move towards opposite poles
what happens during telophase II?
- Nuclei , nuclear envelopes, and nucleoli form
- Chromosomes de-condense
- Cytokinesis occurs
what is the product of meiosis II?
- Four haploid daughter cells are formed
- Each cell is genetically unique due to crossover in prophase of meiosis I
how are mitosis and meiosis different?
Meiosis:
1. reduces the number of chromosome sets - from one diploid cell to four haploid cells 2n –> n
2. produces daughter cells that are genetically different from the parent cell and each other
Mitosis:
1. conserves the number of chromosome sets n–> n 2n –> 2n
2. produces daughter cells that are genetically identical to the parent cell and each other
what causes the 4 daughter cell to be genetically different from one another and the parent cell?
the cross over that happens in prophase I –> allows the different alleles to mix between homologous chromosomes from paternal and maternal sets
what are 4 unique things that occur during meiosis I?
- Homologous chromosomes pair during prophase
- Non-sister chromatids exchange DNA during
prophase - Paired homologous chromosomes line up on the
metaphase plate during metaphase - Homologous chromosomes separate during
anaphase
