Meiosis Flashcards
What do mitotic cells function in?
Growth, replacement of damaged or lost cells, and asexual reproduction.
What is the involvement of meiosis in sexual reproduction?
The formation of gametes (eggs and sperm)
What happens to the number of pairs of chromosomes in meiosis?
The number of pairs is reduced from 2 pairs to 1 pair (in the gametes).
How many sets are received by the daughter cells in meiosis and mitosis?
In meiosis, 1 complete set is received by the gametes. In mitosis, every cell gets an exact copy of the complete genetic info (both sets).
Why is meiosis necessary?
Because the number of pairs of chromosomes must be kept constant in the future generations. (otherwise there would be a doubling every generation)
How is called the fusion of two gametes?
Fertilization
What cell does the fusion of two gametes (haploid) produce?
A diploid zygote
What alternates in life cycles for sexually reproducing organisms?
Haploid and diploid stages alternate. The length of each depends on the life cycles.
What happens with diploid zygotes?
They undergo mitosis to give rise to all cells in the body.
How are called the cells (2n) that are set aside for meiosis and what do they produce?
Germ-line cells and they prodduce gametes (n).
Does the interphase vary before meiosis and mitosis?
No, it is the same. Chromosomes are copied in S phase, and there is a formation of spindle and chromosome shortening in the G2 phase.
How many daughter cells are resultant after the 2 meiosis?
A total of 4 daughter cells.
What are homologuous chromosomes?
Two chromosomes in a pair that contain the same linear sequence of genes. Each homologue was equally contributed by eeach parent
Ex:
Dad set: 1, 2, 3, 4,…, 23
Mom set: 1, 2, 3, 4,…,23
The #1s have the same genes and form a homologuous pair
When does the cell become haploid?
The two daughter cells become haploid after telophase 1/interkinesis
What are the phases of meiosis 1?
Prophase 1, metaphase 1, anaphase 1, telophase 1, and interkinesis.
What happens in prophase 1?
Nuclear enveloppe disappears, nucleolus disappears, centrioles are at the opposite sides of the cell, spindle apparatus forms, homologues become closely associated in synapsis, and crossing over occurs.
What happens in metaphase 1?
Microtubules from opposite poles attach to each homologue, not each sister chromatid. Homologues (tetrads) are aligned at the metaphase plate. The orientation of each homologue is random.
How are homologues attached in meiosis?
They are attached with chiastama. The kinetochores fuse and the microtubules can only attach to one side of each centromere.
What happens in anaphase 1?
The homologues are separated from each other and the sister chromatids remain attached at the centromere.
What happens in telophase 1?
The nuclear enveloppe may form around each set of chromosomes. Each nucleus is now haploid. Both sister chromatids are now not identical because of crossing over.
What happens in interkinesis?
The cytoplasm of the cell divides into 2. However, no cell cycle occurs after that (DNA replication, etc). The cells rest prior to second set of division.
What happens in prophase 2?
Nuclear enveloppe disappears if it reformed. New spindle forms.
What happens in metaphase 2?
Spindle fibers from opposite poles bind to kinetochores of each non-identical sister chromatid. They align on the metaphase plate.
What happens in anaphase 2?
Spindles contract and the cohesion complex joining the centromeres break and chromatids separate. Non identical sister chromatids are moved to opposite poles.
