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Title: Mitosis and Meiosis
Description: These notes explore the two mechanisms by which cells divide: mitosis and meiosis. The differences between the two mechanisms is discussed, as well as different DNA biotechnology. These notes were taken for an introductory college biology course.
Description: These notes explore the two mechanisms by which cells divide: mitosis and meiosis. The differences between the two mechanisms is discussed, as well as different DNA biotechnology. These notes were taken for an introductory college biology course.
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Mitosis and Meiosis
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One reason DNA is replicated is in order to facilitate cell division
Prokaryotes and single celled eukaryotes reproduce asexually via cell division
Requires the entire genome to be replicated
o Prokaryotes: binary fission
o Eukaryotes: mitosis
Mitosis
o Eukaryotic cells use it for growth and repair of damaged tissues
▪ DNA is divided among several chromosomes, each chromosome being
strand of DNA
o Not used to form gametes (sex cells)
o Before division:
▪ Chromosomes are not visible
▪ DNA loosely arranged in nucleus
▪ DNA condenses into chromosomes right before the cell divides
o Chromosomes
▪ Made up of two sister chromatids
• Identical molecules of DNA as a result of replication
▪ Most eukaryotic organisms have two sets of each chromosome
• Homologous chromosomes
• Each one has DNA with the same genes
• If you have two sets of chromosomes, you are diploid
▪ Humans typically have 46 chromosomes, 23 from mum and 23 from dad
• In some cases, individuals have atypical numbers of chromosomes
o Basics of Mitosis
▪ Begins with one parent cell
▪ All of the DNA is replicated
▪ In eukaryotes, DNA condenses into chromosomes
▪ Cell divides, and each daughter cells gets an identical set of DNA
o The Cell Cycle
▪ Alternation of activities between processes related to growth and division
▪ Interphase
• ~90% of the time the cell is in a stage of cell growth in which regular
cellular functions are carried out
• DNA replication and chromosomal condensation takes place
• Nuclear membrane breaks down
▪ Cell division: mitosis and cytokinesis
• Nuclear membrane breaks down
• Chromosomes line up at the center of the cell
• Sister chromatids separate
• New nuclear membranes being to form
• Cytokinesis occurs
▪ Cell Cycle Regulation
• Checkpoints are parts of the cell cycle that prevent the cell from
continuing on in the cycle until the last process is complete
Mitosis and Meiosis
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If the checkpoints do not work…
• Cancer caused by unrestrained cell division
• Loses contact inhibition, which is the ability to stop dividing
after coming into contact with normal cells
• Loss of balance between cell division and cell death
Meiosis
o A somatic cell is a diploid with 46 chromosomes
o Gametes are haploid cells with 23 chromosomes, and fertilization restores the
diploid #
o Meiosis halves the number of chromosomes in daughter cells and creates
gametes
o Homologous chromosomes have the same genes, but are not genetically
identical
▪ Each chromosome is replicated to form a sister chromatid
o Due to genetic variation, species are more likely to prevail during ecological
disasters
o Overview
▪ Takes place in two rounds of division
▪ Meiosis I halves the number of chromosomes and shuffles genetic info
(diploid cell to two haploid cells)
• Replicated chromosomes condense
• Homologous chromosomes line up
• Crossing over occurs
• A segment from the maternal chromosome swaps with a
segment from the paternal chromosome
• One of the ways that meiosis produces a lot of genetic variation
• Homologous chromosomes separate
• Independent assortment occurs
• The chromosomes at each pole are a random assortment of
paternal and maternal chromosomes
• Cytoplasm divides and results in two haploid cells
▪ Meiosis II produces 4 non-identical haploid daughter cells (gametes)
• In each new haploid daughter cell, the chromosomes will line up in
the middle of the cell and the sister chromatids will be pulled apart
• Results in 4 haploid, non-identical daughter cells
DNA Biotechnology
o DNA Sequencing is used to find out the sequence of DNA bases
o Uses include
▪ Studying disease and disorders caused by mutations
▪ Understanding organismal physiology
▪ Studying evolutionary patterns among different species
o Next Gen sequencing
▪ Began around ten years ago and can now sequence millions of bp/run
▪ Specialized instrument simultaneously targets many areas of DNA
Mitosis and Meiosis
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Has revolutionized DNA sequencing and used in all areas of DNA research
GMOs are genetically modified organisms, used a lot in agriculture
▪ Insert genes from one organism into another organism
• Insert into crops for drought, insect, and pesticide resistance
Gene therapy is inserting a functional copy of a gene into a patient
▪ Tay-Sachs, Multiple Sclerosis, Huntington's Disease, etc
▪ Must have a vector that is used to carry the functional gene to the patient's
DNA, such as viral vectors or gene guns
Other technologies include cloning, stem cell research, forensics, family history,
and CRISPR
Bioethics: you must consider the ethical concerns with all of these technologies
Title: Mitosis and Meiosis
Description: These notes explore the two mechanisms by which cells divide: mitosis and meiosis. The differences between the two mechanisms is discussed, as well as different DNA biotechnology. These notes were taken for an introductory college biology course.
Description: These notes explore the two mechanisms by which cells divide: mitosis and meiosis. The differences between the two mechanisms is discussed, as well as different DNA biotechnology. These notes were taken for an introductory college biology course.