Chapter 13 Meiosis
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What are gametes?
Reproductive cells such as sperm and eggs
What is Meiosis?
Nuclear division that leads to a halving of chromosome number and ultimately to the production of sperm and egg.
What are sex chromosomes?
The X and Y chromosomes.
What is an autosome?
What is a gene?
A gene is a section of DNA that influences some hereditary trait in an individual.
What is an allele?
Term used to denote different versions of the same gene.
What is a karyotype?
The number and types of chromosomes present.
What is a diploid?
Two versions of each type of chromosome
What is a haploid?
Organisms whose cells contain just one of each type of chromosomes
What does the letter "n" represent?
The number of distinct types of chromosomes in a given cell (haploid number).
What is a ploidy?
The combination of the number of sets and n is termed the cell's ploidy
What is a maternal chromosome?
chromosomes that come from the mother
What is a paternal chromosome?
Chromosomes that come from the father
Structure made up of DNA and proteins; carries the cell's hereditary information
A chromosome that consists of one double-helical molecule of DNA packaged with proteins
The two identical chromatid copies in a replicated chromosome
A chromosome that has been copied; consist of two identical chromatids, each containing one double-helical DNA molecule
in a diploid organism, chromosomes that are similar in size, shape, and gene content.
chromatids belonging to homologous chromosomes
Homologous replicated chromosomes that are joined together during prophase I and metaphase I of meiosis.
What is gametogenesis?
A process that forms egg cells or sperm cells.
Uncondensed chromosomes replicate in parent cell.
Early prophase I
Chromosomes condense, spindle apparatus forms, nuclear envelope begins to break down. Synapsis (pairing) of homologous chromosomes.
Late Prophase I
Chiasmata (crossover points) visible, nuclear envelope broken down. Often multiple chiasmata between non-sister chromatids.
Migration of bivalents to metaphase plate is complete
Homologs separate and begin moving to opposite poles of the spindle apparatus.
Telophase I and Cytokinesis
Chromosomes move to opposite poles of the spindle apparatus; spindle apparatus disassembles.
Spindle apparatus forms
Chromosomes line up at middle of the spindle apparatus.
Sister chromatids separate, begin moving to opposite poles of the spindle apparatus.
Telophase II and Cytoknesis
Chromosomes move to opposite poles of the spindle apparatus; spindle apparatus dissembles.
What is crossing over?
The process where the reciprocal exchanges between different homologs create non-ssiter chromatids that have both paternal and maternal segments.
What are the key differences between Meiosis and Mitosis?
- Number of cell divisions: 1 for MT 2 for MI
- Number of chromosomes in daughter cells compared with parent cell: Same for MT half for MI
- Synapsis of homologs: No for MT yes for MI
- Number of crossing-over events: None for MT one or more per pair of homologous chromosomes MI
- Makeup of chromosomes in daughter cells: Identical for MT Different- various combinations of maternal and paternal chromosomes, paternal and maternal segments mixed within chromosomes.
- Role in organism life cycle: Asexual reproduction in some eukaryotes; cell division for growth MT Halving of chromosomes number in cells that will produce gametes
What are the key events of prophase 1?
- 1. condensation
- 2. pairing
- 3. synapsis (bivalent formation)
- 4. partial separation of homologs
Why do mistakes occur?
Trisomy and other meiotic mistakes are random errors that occur during meiosis
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