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30 Cards in this Set

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A form of cell division that halves the number of chromosomes when forming specialized reproductive cells.
What is meiosis divided into?
It includes two divisions of the nucleus-meiosis one and meiosis two- and each division is subdivided into prophase, metaphase, anaphase, and telophase.
What kind of chromosomes does Meiosis begin with?
homologous chromosomes-similar in size shape, and genetic content.
Meiosis- Prophase 1
1. The chromosomes condense
2. The nuclear envelope breaks down
3. Homolougous chromosomes pair all along their length and then cross over.
(Crossing over occurs when portions of a chromatid on one homologous chromosome are broken and exchanged with the corresponding portions on one of the chromatids of the other homologous chromosome. )
Metaphase 1
PAirs of homologous chromosomes move by the spindle to the equator of the cell.
Anaphase 1
The homologous chromosomes seperate.
- The cchromosomes of each pair are moved to opposite poles. Though their genetic info has recombined, the chromatids are still attached at the centromere.
TElophase 1
1. INdividual chromosomes gather at teh poles.
2. The cytoplas divides, creating two new cells.
3. Both cells or poles contain one chromosome from each pair of the homologous ones.
Prophase 2
A new spindle forms around the chromosomes.
Metaphase 2
The chromosomes line up along the equator and are attached at their centromeres to Spindle fibers.
Anaphase 2
CEntromeres divide.
Chromatids, now called chromosomes, move to opposite poles of the cell.
Telophase 2 and cytokinesis
A nuclear envelope forms around each set of chromosomes.
The spindle breaks down, and the cell undergoes cytokinesis.
The result of meiosis is four haploid cells.
What are the three mechanisms that make key contributions to Meiosis?
independent assortment, crossing-over, and random fertilization
Independent Assortment-definition
The random distribution of homologous chromosomes during Meiosis.
eg. The Chromosome that an offspring receives from each of the 23 pairs is a matter of chance.
Crossing over and random fertilization
enhances that yes, there are over 8 million gene combination options. a lot. si. ke paso.
What is the importance of generating variation?
Meiosis and the joinign of gametes are essetial to evolution.
eg. Thouroughbred racehorses are all descendants of a small number of individuals, and selection for speed has accomplised all it can with this limited amount of genetic variation. THe winning times in major races stopped improving decades ago.
The process by which sperm are produced in male animals. It occurs in the testes,
Sperm/sperm production
A diploid cell first increases in size and becomes a large germ cell. The large cell then undergoes Meiosis 1. Two cells are produced, each of which undergoes Meiosis 2 to form 4 haploid cells. The four cells change in form and develop a tail to become male gametes called Sperm.
The process by which gametes are produced in female animals. Occurs in ovaries.
Ovum/Ovum production
The cell that is divided and gets most of the cytoplasm in Meiosis 1/cytokinesis will be the eventual egg cell. The larger cell undergoes Meiosis 2, and the larger cell develops into a gamete called the ovum, or egg. BEcause it has most of the cytoplasm, there are many nutrients to house a fertilized egg.
Asexual Reproduction
A single parent passes copies of all its genes to each of its offspring; there is no fusion of haploid cells such as gametes.
An indivisual produced by asexual reproduction. It is genetically identical to its parent.
Sexual Reproduction
Two parents each form haploid reproductive cells, which join to form offspring. Since both parents contribute genetic material, the offspring have traits of both parents but not exactly identical.
What are a few types of asexual reproduction?
Binary fission; seperation into equal size. Fragmentation; body breaks into several pieces. Budding; new creatures split off from exsisting.
What are some of the problems with asexual reproduction?
Since there is no change in the organism, the new organisms would not be able to adapt to a new enviornment. Sexual reproduction, however, makes different combinations of traits.
What are the three types of sexual life cycles?
haploid, siploid, or alteration of generations.
Haploid life cycle
Simplest of all life cycles.
-Haploid cells occupy the majo portion of this cycle, the zygote is the only diploid cell and creates new haploid cells in Meiosis immediatley after its formation. The haploid cells gie rise to haploid multicellular individuals that produce gametes by Mitosis. In fusion, the gametes fuse to form a diploid zygote.
- When the diploid zygote undergoes Meiosis, the cell repairs damages needed right before crossing over.
-THis type of life cycle found in many protists.
Diploid Life Cycles
Gametes(sperm and egg) join in a process called fertilization, which results in a diploid zygote. After fertilization, teh resulting zygote begins to divide by Mitosis. The single diploid cell eventually gives rise to all the cells of the adult. (THe cells of the adult are also diploid since they are produced by mitosis)
- The diploid individual that develops from the zygote occupies the major portion of the diploid life cycle. The gametes are the only haploid cells in the diploid life cycle; all others are diploid.
Alteration of generations
PLants, algae, and some other protists have a life cycle that regularly alternated between a haploid phase and a diploid phase.
eg. moss, p 152
Sporophyte= the diploid phase in the life cycle that produces spores.
Spore= A haploid reproductive cell produced by Meiosis that is capable of developing into an adult without fusing with another cell.
THe haploid phase that produces gametes by mitosis. (The sporophyte and the gameophyte generations alternate in the life cycle.)