Meiosis Flashcards
What type of cell occurs in meiosis?
Reproductive cell: sex cells and gametes = reproduce
How many times do the cells divide in meiosis?
Two times
What happens in the first stage of meiosis?
1 parent cell divides into 2 daughter cells.
What happens in stage II of meiosis?
2 daughter cells divide into total of 4 daughter cells.
Define meiosis
meiosis is a process that contributes to genetic variety. It also doesn’t make body cells; it makes gametes (sperm and egg cells). It’s also a process where a single cell divides twice to produce four cells containing half the original amount of genetic information. These four daughter cells only have half the number of chromosomes of the parent cell; they are haploid.
Define centromere
Part of chromosomes where sister chromatids are connected.
If 46 chromosomes replicate, how many chromosomes and chromatids are there?
Still have 46 chromosomes but 92 chromatids.
What happens before meiosis?
Interphase occurs before meiosis
Describe Prophase I
In prophase I, the chromosomes condense, thicken, and line up with their homologous pairs. When they find their pair, a process called crossing over takes place and makes recombinant chromosomes, which contributes to the variety of siblings they can have when they have the same parents.
Describe metaphase I
The homologous pairs of chromosomes align on either side of the equatorial plate.
Describe anaphase I
The spindle fibres contract and pull the homologous pairs, each with two chromatids, away from each other and towards each pole of the cell.
Describe telophase I
We end with telophase I, where we have two newly formed nuclei and end meiosis I with two new cells. Cytokinesis follows with splitting the cytoplasm.
Describe prophase II
In each of the daughter cells, a new spindle forms, the nuclear envelope breaks down, and the chromatin condenses into chromosomes again.
Describe metaphase II
The chromosomes are going to line up in the middle of the cell in a single file line. They are not lined up in pairs compared to metaphase I.
Describe anaphase II
During anaphase II, microtubules from each spindle attach to each sister chromatid at the kinetochore. The sister chromatids then separate, and the microtubules pull them to opposite poles of the cell.
Describe telophase II
The chromosomes gather at the 2 poles of the cell, and the cell divides, forming 2 daughter cells from each of the two cells from meiosis I, making four cells. The nuclei also start reforming.
What is the end result of meiosis?
From the processes of independent assortment and crossing over, we have the result of variety. e.g., male sperm cells: 4 sperm cells are all different from each other and are produced each time. They were also different from the starting cell because the starting cell had 46 chromosomes. The ending cells had 23. They are not identical to the original and are not identical to each other. This leads to variety, which is why two siblings with the same parents look different from each other. They are still developed from a unique egg and unique sperm cell that came together.
Define nondisjunction
Nondisjunction is when a cell can receive too many or too few chromosomes in the separation. This contributes to some genetic disorders.
