Module 1.2 Meiosis intro & prophase I Flashcards
Meiosis produces a total of ___ cells from each original ___ cell.
Meiosis superficially resembles two ___ without an intervening period of DNA replication.
four haploid cells
diploid cell
mitotic divisions
Haploid cells can become or give rise or become gametes, which through ___(___) support sexual reproduction and a new generation of diploid organisms.
union (fertilization)
Summary of the meiotic divisions (2)
First meiotic division
- includes a LONG PROPHASE where homologous chromosomes become closely associated and exchange of hereditary material takes place.
- reduction of chromosome number takes place
- two haploid cells produced
Second meiotic division
- Haploid cell divides mitotically into four haploid cells
The ___ of first meiotic division is very significant phase because the most cytogenetical events such as ___ and ___ occur during this phase.
prophase
synapsis
crossing over
The stages of prophase 1, the longest meiotic division (5)
Lepotene
Zygotene
Pachytene
Diplotene
Diakinesis
In the ___ substage of prophase I, chromosomes become more uncoiled and assume a long thread-like shape.
The ends of the chromosomes converge toward one side of the nucleus, this is called the ___
Along each chromosome are ___, localized condensaqtions that resemble beads on a string.
Centrioles duplicate at the opposite poles of the cell.
Leptotene/Leptonema
bouquet stage
chromomeres
In the ___ substage of prophase I, The pairing of homologous chromosomes takes place. These chromosomes come from the mother (___) and father (___).
This pairing is known as ___.
Zygotene/Zygonema
Oocyte
Sperm
Synapsis
Types of synapsis (3)
Proterminal synapsis
- end to centromeres
procentric synapsis
- centromeres to ends
localized pairing / random synapsis
- various points
The homologous chromosomes are joined by a roughly 0.2um thick protein-containing framework called a ___.
This extends along the chromosomes to the nuclear envelope. This is what facilitates the ____ also known as recombination or crossing over.
synaptonemal complex (SC)
cytogenetical activity
Organisms in which crossing over does not occur and therefore has no synaptonemal complex
Drosophila melanogaster
It is upon completion of the Zygotene stage that paired homologous chromosomes are called ___ or ___
Both members have replicated their DNA but it’s not visually apparent each member is a double structure.
bivalents
tetrads
In the ___ substage of prophase I, the pair of chromosomes continue to coil and shorten and further development of the synaptonemal complex.
This is where the important genetic phenomenon called “___” takes place. Reshuffling and redistribution and mutual exchange of hereditary material.
Pachytene / Pachynema
Crossing over
T or F: the doubling of the DNA molecule strands which is necessary for the duplication of chromosomes occurs in the Pachytene stage
F, this occurs even before the beginning of meiotic prophase
However, the chromatids become partially independent despite being linked together by their centromere
Each synaptonemal pair in the pachytene phase is called a ___or ___ because it consists of two visible chromosomes
bivalent or dyad
Chromatids may divide transversely by the help of an enzyme called the ___.
Broken chromatid segments are united by the enzyme ___.
Endonuclease
Ligase
In the ___ substage of prophase I, The synaptonemal complex disassembles and the homologous chromosomes begin to move apart.
The ___ shows the result of crossing-over. This is where homologous chromosomes are very tightly associated.
Diplotene/Diplonema
Chiasma
___ is followed rapidly by the remaining stages of meiosis. However, in many animals the oocytes can remain in that form.
Diplonema
Example of diplonema in humans
In human females, their oocytes go through meiosis I up until diplonema up until the seventh month of fetal development and then remain arrested in this stage for many years.
If an egg is fertilized it completed meiosis II and a functional zygote is produced
In the ___ substage of prophase I, the chromosomes condense even more making it now posssible to see the four members of the tetrads
The chiasmata are clearly visible at this stage.
The nucleolus detaches and disappears. Nuclear envelope breaks down.
diakinesis
In diakinesis, Chiasma moves from centromere towards the end of the chromosomes and the immediate chiasmata diminish, this is called ___.
Chromatids remain connected to the terminal chiasmata up until metaphase
Terminalization
T or F: The synapsis and crossing-over phenomena applies only to homologous chromosomes the autosomes.
False, this can also apply to the Y chromosome of eutherian (placental) mammals.
This is due to their PARs or (Pseudo-autosomal regions) which is very important otherwise it will make the man sterile.
T or F: Rodents and Mammals have PARs
F, it is not necessary for them.
