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Transcript of Meiosis
Homologous: similar in shape and size
Two chromosomes carry the same genes
One from father, one from mother
Diploid cell: 46 chromosomes, 23 pairs of homologous genes Meiosis I Metaphase I Telophase I Prophase I Interphase I Anaphase I Period between cell division
DNA unzips into 2 strands
2 pairs of centrioles lie next to nucleus Spindle fibers formed from centrioles
Homologous chromosomes are attracted to each other and crossing over occurs Crossing over is the exchange of genetic material from homologous chromosomes. This rearranges the alleles on each chromosome. Homologous chromosomes line up along the metaphase plate (cell's equator)
Nuclear membrane disperses Spindle fibers from poles attach to chromosomes and pull them to opposite poles of cell
Sister chromatids do not separate Spindle fibers disentegrate
Nuclear membrane formed around new group of chromosomes Clone Wars/Transition period between Meiosis I and Meiosis II Post-Meiosis I Cytokinesis- cell splits into two different cells The two new cells are haploid However, sister chromatids are still intact which makes the S phase unnecessary The two new haploid cells are now ready for Meiosis II Meiosis II Meiosis II follows the same basic steps as mitosis save for a few minor details Prophase II Metaphase II Anaphase II Telophase II Chromosomes condense and become visible
Spindle fibers formed from centrioles Nuclear membrane diperses
Chromosomes line up along metaphase plate
Spindle fibers attach to each sister chromatid at centromere Spindle fibers pull chromosomes apart, separating sister chromatids and forming two sets of chromosomes
Because of the random orientation of the chromosomes, it is random which chromatid gets pulled toward one side Chromosomes group up on opposide poles and a new nuclear membrane forms around each
*Cytokinesis follow as the rest of the cell and cytoplasm completely divides REMINDER: This happens twice as there are now two cells from meiosis I. Possible errors in Meiosis
Non-disjunction Non-disjunction: two or more homologous chromosomes do not separate during anaphase, stick together, and both go to same pole of cell For humans this results in an egg or sperm cell receiving 24 genes instead of 23 Non-disjunction can happen to any chromosome all of which will have the effect of altering the future child, even fatally in severe occasions Down Syndrome Non-disjunction in 21st pair
Child receives 3 chromosomes instead of 2.
This is called a trisomy where 3 chromosomes are inherited Meiosis is now complete! Karyotypes:
Photo of the chromosomes in a cell organized by size and shape
There are two ways to obtain chromosomes for karyotyping
One is amniocenteses where a large needle is used to extract the amniotic fluid surrounding a baby which contains its cells
Second is by chronic villus sampling, which involves obtaining a tissue sample of the placenta's imprinted projections of the uterus wall Analysis of a karyotype
Sex of a human can be determined by examining 23rd pair and whether or not it is XX or XY
Also, dis-junction can be checked by examining whether a pair of chromosomes has an extra chromosome Overview Meiosis: A process in which a parent diploid cell divides into four haploid daughter cells.
Meiosis consists of two separate cell divisions, first the diploid cell splits into two haploid cells, followed by those cells splitting again.
Errors such as dis-junction can lead to alteration in characteristics of future organism.
Karyotype's can be used to efficiently analyze and examine an organism's chromosomes even before it is fully developed and predict possible outcomes or changes in the future.
Never Forget... May the force be with you. Luke VonEschen Hour 3