Cell Division Flashcards
What is mitosis?
Mitosis is a form of nuclear division that produces genetically identical daughter nuclei containing the same number of chromosomes as the parent nucleus.
What happens during prophase I?
Chromatin threads condense, coil and shorten to become chromosomes.
Homologous chromosomes pair along their whole length, with one chromosome coming from the male parent and the other from the female parent. As the chromosomes shorten further, homologous chromosomes appear to repel each other. These chromatids of homologous chromosomes may cross and twist around one another, resulting in a cross over. Asters form around the centrioles and the nuclear envelope and nucleolus disappear. Spindle fibres form.
What happens during metaphase I?
Pairs of homologous chromosomes arrange themselves along the equatorial plane of the spindle. The two chromosomes of each pair face opposite poles of the cell. Each chromosome is attached to a spindle fibre.
What happens during anaphase I?
Homologous chromosomes separate and are pulled to opposite poles of the cell as spindle fibres shorten.
What happens during telophase I?
A nuclear envelope forms around the chromosomes at each pole and the cytoplasm divides.
What happens during cytokinesis I?
The cytoplasm cleaves into two, producing two daughter cells, each with a haploid number of chromosomes. The centrioles divide.
What happens during prophase II?
The two pairs of centrioles move to opposite poles of the cell. The nuclear membrane disappears and spindle fibres appear.
What happens during metaphase II?
Chromosomes arrange themselves along the equatorial plane of the spindle.
What happens during anaphase II?
The centromeres divide. Sister chromatids separate to become daughter chromosomes, which are pulled towards opposite poles of the cell.
What happens during telophase II?
The spindle fibres disappear. Nuclear envelopes form around the two daughter chromosomes at each pole. A nucleolus reforms.
What happens during cytokinesis II?
Cleavage of cytoplasm results in four daughter cells being produced, each with half the number of chromosomes as the parent cell.
Why is meiosis important?
- Produces haploid gametes -> allows for fusion and maintenance of normal diploid number of chromosomes
- Gamete variation due to crossing over and independent assortment -> higher chance of survival
What is the difference between mitosis and meiosis.
For mitosis, daughter cells contain the same number of chromosomes as the parent cell; however, it is half for meiosis.
Pairing of homologous chromosomes does not occur; however, for meiosis, crossing over may occur.
Daughter cells are genetically identical to the parent cell, unlike meiosis
Two daughter ells are produced from one parent cell during mitosis; however it is four for meiosis
Mitosis involves only one nuclear division while meiosis involves two
Mitosis occurs in normal body cells while meiosis occurs in the gonads during formation.
