Chapter 4.4: Meiosis: Cell Divisions That Halve Chromosome Number Flashcards
What phase of meiosis does the nuclear membrane breaks down and the spindle begins to form?
diakinesis of prophase I of meiosis I
What phase of meiosis does Sister chromatids attach to fibers from the same pole?
metaphase I
What are somatic cells?
• The mitotically dividing and G0-arrested cells are the so-called somatic cells whose descendants continue to make up the vast majority of each organism’s tissues
Describe prophase II (3)
Chromosomes condense
Centrioles move toward the poles
The nuclear envelope breaks down
What phase: Cytokinesis?
telophase II
What phase of meiosis does • Chromatids thicken and shorten?
diakinesis of prophase I of meiosis I
Describe the difference between mitosis and meiosis in term of number of divisions
Mitosis: One round of division
Meiosis: Two rounds of division, meiosis I and meiosis II
Describe the difference between mitosis and meiosis in term of products
Mitosis: Mitosis produces two new daughter cells, identical to each other and the original cell. Mitosis is thus genetically conservative
Meiosis: Meiosis produces four haploid cells, one (eggs) or all (sperm) which can become gametes. None of these is identical to each other or to the original cell, because meiosis results in combinatorial change
What phase of meiosis does • Homologous chromosomes enter synapsis?
zygotene of prophase I of meiosis I
Describe pachytene of prophase I of meiosis (2)
- Synapsis is complete
* Crossing-over, genetic exchange between nonsister chromatids of a homologous pair, occurs
What phase of meiosis does • Chromosomes thicken and become visible, but the chromatids remain invisible?
leptotene of prophase I of meiosis I
What phase of meiosis does Homologous chromosomes move to opposite poles?
anaphase I
What phase: Chromosomes condense?
prophase II
What phase of meiosis does • A tetrad of four chromatids is visible?
diplotene of prophase I of meiosis I
What phase of meiosis does Tetrads line up along the metaphase plate?
metaphase I
What phase of meiosis does • The synaptonemal complex forms?
zygotene of prophase I of meiosis I
When does each of the two daughter nuclei divides, resulting in four nuclei?
meiosis I
Describe telophase II (3)
Nuclear membranes re-form, and cytokinesis follows
Chromosome begins to uncoil
Cytokinesis- the cytoplasm divides, forming four new haploid cells
What phase: Sister chromatids attach to spindle fibers from opposite poles?
metaphase II
Describe the difference between mitosis and meiosis in term of which cells undergo
Mitosis: Haploid and diploid cells can undergo mitosis
Meiosis: Only diploid cells undergo meiosis
Describe zygotene of prophase I of meiosis (2)
- Homologous chromosomes enter synapsis
* The synaptonemal complex forms
What are germ cells?
cells destined for a specialized role in the production of gametes
Describe metaphase II (2)
chromosomes align at the metaphase plate
Sister chromatids attach to spindle fibers from opposite poles
What phase of meiosis does • Crossing-over, genetic exchange between nonsister chromatids of a homologous pair, occurs?
pachytene of prophase I of meiosis I
How does meiosis contribute to genetic diversity?
o Because only chance governs which paternal or maternal homologs migrate to the two poles during the first meiotic division, different gametes carry a different mix of maternal and paternal chromosomes (2n combinations)
o The reshuffling of genetic information through crossing-over during prophase I, ensures an even greater amount of genetic diversity in gametes
What phase: Chromosome begins to uncoil?
telophase II
What phase of meiosis does • Centromeres begin to move toward opposite poles?
leptotene of prophase I of meiosis I
Describe the difference between mitosis and meiosis in term of splitting of centromere
Mitosis: The centromere splits at the beginning of anaphase
Meiosis: The centromere does not split during meiosis I; The centromere splits at the beginning of anaphase II
What is synapsid chromosome pair containing two chromosomes?
bivalent