Chapter 11.3: The Process of Meiosis Flashcards
What is the accurate segregation of homologues during meiosis I without the formation of chiasmata between homologues?
achiasmate segregation
What is the final result of meiosis?
o The final result of this division is four cells, each containing a complete haploid set of chromosomes
What happens during anaphase II?
o Anaphase II- the spindle fibers contract, and the cohesin complex joining the centromeres of sister chromatids is finally destroyed, allowing sister chromatids to be pulled to opposite poles
Define achiasmate segregation
the accurate segregation of homologues during meiosis I without the formation of chiasmata between homologues
What happens during prophase I?
o In Prophase I:
DNA coils tighter
Individual chromosomes first become visible
Homologous chromosomes become closely associated in synapsis and exchange segments by crossing over
What happens in metaphase I?
o In Metaphase I:
Bivalents capture spindle fibers and move to the center of the cell, where they are aligned as paired homologues and not individual chromosomes
Microtubules from opposite poles become attached to the kinetochores of homologues
Random orientation of each pair of homologues on the spindle axis
What happens in anaphase I?
Microtubules of the spindle fibers begin to shorten
As they shorten, the connection between homologues at chiasmata are broken, allowing homologues to be pulled to opposite poles
How are the four chromatids held together?
The four chromatids are held together in two ways:
• The two sister chromatids of each homologue, the products of DNA replication, are held together by cohesion proteins (sister chromatid cohesion)
• Exchange of material by crossing over between homologues locks all four chromatids together
What happens in telophase I?
o In Telophase I:
The chromosomes have segregated into two clusters, one are each pole of the cell
Nuclear membrane re-forms around each daughter nucleus
What are aneuploid gametes?
o Gametes with an improper number of chromosomes are called aneuploid gametes
What happens during metaphase II?
o Metaphase II- in metaphase II, spindle fibers from opposite poles bind to kinetochores of each sister chromatid, allowing each chromosome to migrate to the metaphase plate as a result of tension on the chromosomes from polar microtubules pulling on sister centromeres
What is sister chromatid cohesion?
The sister chromatids of each homologue are also joined by the cohesin complex in a process called sister chromatid cohesion
What is nondisjunction?
o Failure of chromosomes to move to opposite poles during either meiotic division is called nondisjunction an it produces one gamete that lacks a chromosome and one that has two copies
Define independent assortment
for genes on different chromosomes this results from the random orientations of different homologous pairs during metaphase I of meiosis. For genes on the same chromosome, this occurs when the two loci are far enough apart for roughly equal numbers of add- and even-numbered multiple crossover events
What is for genes on different chromosomes this results from the random orientations of different homologous pairs during metaphase I of meiosis. For genes on the same chromosome, this occurs when the two loci are far enough apart for roughly equal numbers of add- and even-numbered multiple crossover events?
independent assortment
