LN 10Cell Division-Mitosis and Meiosis
Cell Division
– Mitosis and Meiosis
Objectives:
After completing this section, you should:
1. be familiar with the Cell Cycle, and understand where the processes of mitosis and meiosis fit into that cycle
2. understand the differences that distinguish mitosis and meiosis, as well as the cell types within which each occurs
3. understand the importance of (a) maintaining a constant chromosome number during mitosis and (b) halving the chromosome number during meiosis
4. recognize the different stages of mitosis and meiosis
5. identify when and shwere crossovers take place
Key Terms: cell cycle centromere chromosome mitosis meiosis interphase prophase metaphase anaphase random segregation independent assortment karotype haploid diploid tetrad kinetochore telophase gamete chromatid homologue (homologous) synapsis crossing over
Online Lesson(s):
Mitosis, Meiosis, and the Cell Cycle
( http://plantandsoil.unl.edu
)
Important Observations by Cytologists
▪ Nuclei of gametes fuse during fertilization
▪
▪ Chromosomes: structures observed in the nucleus
▪ Chromosome number per cell varies from species to species
▪ Chromosome number is the same in all cells of a given species
▪ Number in somatic cell = 2x number in gametes
Somatic cells: chromosomes are only found in pairs -- Diploid
▪
▪ Gametes: only one of each type of chromosome -- Haploid
During cell division, chromosomes segregate in an orderly fashion.
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What do these observations indicate about nuclear division?
Two Types of Nuclear Division
Mitosis
Starts with Ends with
Diploid ----------- Diploid
1 somatic cell ------ 2 daughter somatic cells
* Chromosome number stays the same
* Genetic complement constant
Meiosis
Starts with Ends with
Diploid ----------- Haploid
1 somatic cell (germ cell) ------- 4 gametes
* Chromosome number is halved
* Genetic complement can vary
1) Random segregation
2) Independent assortment
3) Crossing-over
The Cell Cycle
Description:
Mitosis
Description:
Prophase
Telophase
Meiosis
Description:
Distinction between Meiosis I and II:
Prophase I
Metaphase I
Anaphase II
Telophase II
Summary drawings to compare mitosis and meiosis:
Comparison of Mitosis and Meiosis
Mitosis Meiosis
Produces identical cells
No homologous pairing, so no crossovers
Centromeres divide at anaphase
Conservative, makes identical cells
Works with any type of cell, haploid or diploid
Produces gametes
Synapsis of homologous to allow for crossovers
Centromeres divide at anaphase II
Gametes will vary genetically
Only works with cells that have chromosomes that can pair such as diploids or tetraploids
