Topic 18 Biology Llanes

Mitosis

a form of asexual reproduction; doesn't normally chromosome # of the original cell; results in the production of 2 genetically identical diploid cells; when the 2 sets of genetic material separate, each daughter cell gets 1 complete set of chromosomes; a single cell division

Telophase I

a nuclear membrane forms around each cluster of chromosomes; cytokinesis follows, making 2 new cells

Meiosis

a process which the # of chromosomes per cell is cut in 1/2 thru the separation of homologous chromosomes in a diploid cell; usually involves 2 distinct divisions

Meiosis

an early step in sexual reproduction; reduces the chromosome # by half; makes 4 genetically different haploid cells; homologous chromosomes line up & then move to separate daughter cells so the 2 alleles for each gene segregate from each other & end up in different cells; needs 2 rounds of cell divisions

Metaphase II

chromosomes line up in the center of each cell

Diploid Cells

contain 2 complete sets of inherited chromosomes & 2 complete sets of genes

Tetrad

contains 4 chromatids

End of Meiosis II

diploid cell becomes 4 haploid cells

Telophase II & Cytokinesis

each of the 4 daughter cells made in meiosis II get 2 chromatids; these 4 daughter cells now have the haploid number (N) - just 2 chromosomes each; all daughter cells are different

Metaphase I

paired homologous chromosomes line up across the center of the cell

Interphase I

prior to meiosis I; cell undergoes a round of chromosome replication - each replicated chromosome has 2 identical chromatids joined at the center; only meiosis I undergoes this phase

3 ways Mitosis and Meiosis differ

replication & separation of genetic material, changes in chromosome number, and numbers of cell divisions

Meiosis I

results in 2 cells (daughter cells) with sets of chromosomes that are different from each other & the diploid cells that started the process

Anaphase I

spindle fibers pull each homologous chromosome pair to opposite ends of the cell; when complete, the separated chromosomes cluster at opposite ends of the cell

Chromosomes

strands of DNA & protein inside the cell nucleus; carriers of genes; genes are located in specific positions on them

Prophase I

the cells start dividing & the chromosomes pair up forming a tetrad; the tetrads undergo a process called crossing-over; a spindle forms & attaches to each tetrad at the end of the phase

crossing over

the chromatids of the homologous chromosomes cross over one another, then, the crossed sections of the chromatids are exchanged; makes new combos of alleles in the cell

Prophase II

the chromosomes don't pair up to form tetrads because the homologous pairs were separated during meiosis I

Anaphase II

the paired chromatids separate

Meiosis II

unlike 1st division, neither cell goes thru a round of chromosome replication before starting division