Meiosis Flashcards
What does sexual reproduction allow?
Genetic Variety.
What are gametes?
Gametes are sex cells;
They undergo meiosis to:
- Create genetic variability and diversity
- Reduce chromosomes from diploid to haploid
- Daughter cells are genetically unique to the parent cell
What are somatic cells?
Somatic cells are body cells;
They undergo mitosis to:
- Grow
- Repair damaged cells
- Replace old or dead cells
- Daughter cells are genetically identical to the parent cell
What does meiosis prevent?
Meiosis prevents the “doubling” of genetic information.
What do fused gametes form after fertilization?
A zygote.
How many chromosomes does each gamete contain?
23 Chromosomes.
How many chromosomes does each zygote contain?
46 Chromosomes.
What is the human life cycle?
Zygote -> Embryo -> Fetus -> Human
How many phases does the gamete production process have?
3 Phases:
- Interphase
- 2 Rounds of meiosis
What are Homologous Chromosomes?
Two matching chromosomes with the
same size, same types of genes in the same locations.
What are Sister Chromatids?
Two identical copies of the same chromosome formed by DNA replication, attached at the centromere.
What happens in Interphase for meiosis?
The DNA replicates itself.
- Before replication, there are 46 chromosomes (46 chromatids)
- After replication, there are still 46 chromosomes (92 chromatids)
What is a tetrad?
Two pairs of Homologous Chromosomes.
What is the purpose of Meiosis 1?
The purpose of meiosis 1 is to reduce the amount of chromosomes by half, also known as the reduction phase.
What happens in Prophase 1? (Meiosis)
- Centrioles move to opposite poles
- Spindle fibres form from centrioles
- Chromatin has condensed to form chromosomes
- The nuclear membrane breaks down
- Genetic recombination occurs between each tetrad; also known as crossing over
What happens in Metaphase 1? (Meiosis)
- Chromosomes line up along equation in pairs (tetrads)
- Line up with their Homologous pair
What happens in Anaphase 1? (Meiosis)
- Chromosome pairs are separated and pulled away to opposite ends by shortening of spindle fibres
- The sister chromatids do NOT separate (different than mitosis)
- Only the tetrad is broken up, but sister chromatids are still attached at the centromere
What happens in Telophase 1? (Meiosis)
- Nuclear membrane reforms (2 of them now)
- Spindle fibres retract
- Cleavage Furrow (starts to pinch)
What happens in Cytokinesis during Meiosis 1?
- Cytokinesis occurs forming two genetically different daughter cells
- Each daughter cell has half (haploid – n) the number of chromosomes as the parent cell (diploid -2n)
Before MEIOSIS I – 46 CHROMOSOMES (92 CHROMATIDS)
After MEIOSIS I – 23 CHROMOSOMES (46 CHROMATIDS)
What is the purpose of Meiosis 2?
Meiosis is the equational division.
- Similar to mitosis, but no duplication of chromosomes during a very short interphase (no G1 or S phase)
- End result – four haploid cells
What happens in Prophase 2? (Meiosis)
- Nuclear membrane begins to break down
- Spindle fibers begin to form
- Centrioles begin to move to poles
What happens in Metaphase 2? (Meiosis)
- Chromosome pairs align along equator of cell.
- Spindle fibers attach to centromeres of chromatids
(chromatids no longer identical because of crossing over)
What happens in Anaphase 2? (Meiosis)
Spindle fibers pull chromatids apart
What happens in Telophase 2? (Meiosis)
- Nuclear membrane re-assembles
- Chromosomes uncoil
- Spindles disappear
