Mitosis and Meiosis Flashcards
What is mitosis?
Cell division, occurs throughout the body and makes somatic cells. Helps you to grow and repair damage.
Interphase
- Not technically a phase of mitosis, but occurs before the process begins.
- During the synthesis phase, DNA is copied, chromosomes are replicated.
- Interphase is the resting stage, where is the cell isn’t actively dividing. The cell spends the most time in this phase, and continues to perform regular cell functions.
- Afterward, chromosomes (chromatids) have doubled, but the cell has 46 chromosomes.
Centromere
Region that holds together each chromosome and duplicate piece of DNA.
Chromatid
An individual chromosome, or piece of DNA.
4 Stages of Mitosis
- Prophase
- Metaphase
- Anaphase
- Telophase
Prophase
- Centrioles move to opposite sides of the cell and form a mitotic spindle.
- The chromosomes condense and become visible
- Nuclear membrane begins to break up.
Centriole
Organelle that helps develop spindle fibers during cell division.
Mitotic Spindle
Bunch of fibers formed during prophase. Attaches to chromosomes at their centromeres, and help to push/pull them during mitosis.
Metaphase plate
Equator/middle of cell.
Metaphase
- Spindle fibers help chromosomes to line up at the metaphase plate.
- Spindle fibers attach to centromeres.
- Centrioles go to opposite poles.
Cleavage furrow
Area where the cell pinches inward.
Anaphase
- Centromere splits in two, so each chromatid separates from its partner.
- Spindle fibers shorten and move new chromosomes to opposite sides of the cell.
- Cell begins physically splitting in two
Telophase
- A nuclear membrane forms in each new cell
- 2 identical daughter cells result, each with 46 chromosomes.
- Cytokinesis occurs
- Afterward, daughter cells enter interphase.
Cytokinesis
Cytoplasm divides, occurring during telophase
Where does mitosis occur in plants?
Only occurs in meristems (growing regions).
Apical meristem
Found at tip of stem and tip of root, allows for growth in length.
Later meristem
Allows for growth in width.
One gene- one protein theory
A gene is a portion of a chromosome that gives rise to one protein molecule. A chromosome contains many genes and could create hundreds of proteins.
Gene expression
A gene is expressed when it creates a protein. A gene is a portion of a chromosome.
Haploid
The amount of chromosomes is half that of the diploid number. 23 in humans. Sex cells (sperm and ova) are haploid.
Zygote
- Diploid cell
2. Formed when a sperm fertilizes an ovum, and begins to undergo mitosis.
What occurs during meiosis?
- The cell undergoes DNA replication during interphase, like during mitosis. At this point, the cells still have 46 chromosomes.
- Replicated chromosomes are split up over the course of 2 sets of divisions.
- First set of division establishes differences between mitosis and meiosis.
Synapsis
Homologous chromosomes line up. 1a finds 1b, etc, forming 23 pairs. These chromosomes are not identical. Consists of 4 chromatids (a tetrad).
Prophase 1
- Normal prophase events occur: chromosomes condense.
- Synapsis occurs
- Crossing over takes place- like segments on homologous chromosomes are exchanged
Recombinant Chromosomes
New chromosomes created by crossing over, which causes variety among offspring. Also means that gametes are not identical, unlike daughter cells created by mitosis.
Metaphase 1
- Chromosomes still line up in the middle of the cell, but they stay in pairs. 23 pairs line up.
- Independent assortment of chromosomes- the way that chromosomes line up during this phase affects the outcome of genetic information in gametes.
- Genes on non homologous chromosomes are inherited independently, linked genes on the same chromosome are inherited together, but can be separated by crossing over.
Anaphase 1
- In meiosis, the centromeres do not divide
2. Homologous pairs separate. A pair of chromatids and a centromere move to opposite sides of the cell.
Telophase 1
- Cells still finish cytokinesis, nuclear membranes form
2. The two new cells have 23 replicated chromosomes of 2 identical chromatids, making them haploid by this phase.
Meiosis 2
- Nearly identical to mitosis
- In interphase 2, the chromosomes don’t replicate.
- The cells are starting with 23 replicated chromosomes
- Forms 4 haploid cells that stop dividing unless fertilization triggers new cell cycles.
Spermatogenesis
- Formation of sperm that requires meiosis
- Starts with a spermatogonium, which undergoes meiosis and produces 4 functional sperm cells.
- Occurs daily, beginning at puberty and lasting for life
Spermatogonium
Diploid cell located in seminiferous tubules located in the testes. Will eventually undergo meiosis.
Where are oocytes found?
The ovaries
Oogenesis
- Formation of female egg through meiosis
- Produces 1 functional ovum from an oocyte every month.
- Occurs on a monthly basis beginning at puberty and ending at menopause (46-53)
Polar bodies
The two daughter cells formed through oogenesis that don’t receive organelles and therefore disintegrate.
Genetic Variation
Genetic differences within or among a population
Causes of genetic variation among offspring
- Independent assortment of chromosomes during metaphase 1 of meiosis
- Crossing over during synapsis in prophase 1 of meiosis
- Random fertilization
