POL sections 7.4, 7.5 Flashcards
Overall functions of meiosis
To reduce the chromosome number from diploid to haploid; To ensure that each of the haploid products has a complete set of chromosomes; to generate genetic diversity among the products (gametes)
Meiosis
two nuclear divisions; one DNA replication; haploid cells genetically different from each other; consists of two nuclear divisions, meiosis I and meiosis II
Meiosis I
Homologous chromosomes come together and line up; Homologous chromosome pairs separate; preceded by DNA replication; at the end, two nuclei form each with half of the original number of chromosomes composed of two sister chromatids
Meiosis II
Not preceded by DNA replication; Sister chromatids are separated; produces four genetically different haploid cells
Shuffling of genetic material
Crossing over and independent assortment
Crossing over
Homologous chromosomes pair by synapsis; four chromatids form a tetras or bivalent; chromatin continues to coil and compact as chromosomes condense; genetic material exchanged between non-sister chromatids
Synapsis
Homologous chromosomes pair by adhering along their lengths in this process that lasts from prophase I to end of metaphase I to form a tetras/bivalent
Chiasmata
X-shaped attachment points of the two homologous chromosomes; genetic material is exchanged between non-sister chromatids
Recombinant chromatids
Contain genetic material from different homologs
Independent assortment
Phenomenon regarding which member of a homologous pair goes to which daughter cell at anaphase I
Nondisjunction
Failure of homologous chromosome pair or chromatids to separate
Aneuploidy
Condition of having an abnormal number of chromosomes
Trisomy
Condition of having one extra chromosome
Monosomy
Condition of missing one chromosome
Most common form of aneuploidy in humans
Trisomy 16 (3 copies of chromosome 16)
Down syndrome
Trisomy 21; allows for survival but such people have intellectual disabilities but can otherwise lead long and productive lives
Polyploidy
Triploid, tetrapods, or higher order; caused by extra round of DNA replication preceding meiosis or no spindle formed in meiosis II; leads to reproductive isolation and speciation
Ploidy
Number of chromosomes in the nucleus
Translocation
Chromatids from non-homologous chromosome pairs break and rejoin; quite common in mitotic cells; may be carried on the gametes that result from meiosis and be passed on to offspring at fertilization
Necrosis
Occurs when cells are damaged by mechanical means or toxins, or are starved of oxygen or nutrients; cells swell up and burst leading to inflammation
Apoptosis
Genetically programmed series of events that result in cell death
Two types of cell death
Necrosis and apoptosis
Reasons for apoptosis
- The cell is no longer needed by the organism
2. The longer cells live, the more prone they are to genetic damage that could lead to cancer
Events of apoptosis
Cell becomes detached from its neighbors; hydrolyzes its DNA into small fragments, forms blebs that break up into cell fragments
Hypersensitive response
Apoptosis used by plant cells in an important defense mechanisms; plant cells digest their own cell contents in the vacuole and then release the digested components into the vascular system
Signal transduction pathways that lead to apoptosis
- Signals from inside (Age of cell or recognition of damaged DNA) or outside the cell (receptors that activate signal transduction pathways
- Activation of class of enzymes called caspases in animals or a functionally similar class of enzymes in plants
- Hydrolyzes target proteins in a cascade of events
- Cell dies as caspases hydrolyze proteins of the nuclear envelope, nucleosomes, and cell membrane
