Module 1.2 Meiosis intro & prophase I

Question 1

Meiosis produces a total of ___ cells from each original ___ cell.

Meiosis superficially resembles two ___ without an intervening period of DNA replication.

Answer 1

four haploid cells

diploid cell

mitotic divisions

Question 2

Haploid cells can become or give rise or become gametes, which through ___(___) support sexual reproduction and a new generation of diploid organisms.

Answer 2

union (fertilization)

Question 3

Summary of the meiotic divisions (2)

Answer 3

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

Question 4

The ___ of first meiotic division is very significant phase because the most cytogenetical events such as ___ and ___ occur during this phase.

Answer 4

prophase

synapsis
crossing over

Question 5

The stages of prophase 1, the longest meiotic division (5)

Answer 5

Lepotene

Zygotene

Pachytene

Diplotene

Diakinesis

Question 6

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.

Answer 6

Leptotene/Leptonema

bouquet stage

chromomeres

Question 7

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 ___.

Answer 7

Zygotene/Zygonema

Oocyte
Sperm
Synapsis

Question 8

Types of synapsis (3)

Answer 8

Proterminal synapsis
- end to centromeres

procentric synapsis
- centromeres to ends

localized pairing / random synapsis
- various points

Question 9

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.

Answer 9

synaptonemal complex (SC)

cytogenetical activity

Question 10

Organisms in which crossing over does not occur and therefore has no synaptonemal complex

Answer 10

Drosophila melanogaster

Question 11

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.

Answer 11

bivalents
tetrads

Question 12

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.

Answer 12

Pachytene / Pachynema

Crossing over

Question 13

T or F: the doubling of the DNA molecule strands which is necessary for the duplication of chromosomes occurs in the Pachytene stage

Answer 13

F, this occurs even before the beginning of meiotic prophase

However, the chromatids become partially independent despite being linked together by their centromere

Question 14

Each synaptonemal pair in the pachytene phase is called a ___or ___ because it consists of two visible chromosomes

Answer 14

bivalent or dyad

Question 15

Chromatids may divide transversely by the help of an enzyme called the ___.

Broken chromatid segments are united by the enzyme ___.

Answer 15

Endonuclease

Ligase

Question 16

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.

Answer 16

Diplotene/Diplonema

Chiasma

Question 17

___ is followed rapidly by the remaining stages of meiosis. However, in many animals the oocytes can remain in that form.

Answer 17

Diplonema

Question 18

Example of diplonema in humans

Answer 18

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

Question 19

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.

Answer 19

diakinesis

Question 20

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

Answer 20

Terminalization

Question 21

T or F: The synapsis and crossing-over phenomena applies only to homologous chromosomes the autosomes.

Answer 21

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.

Question 22

T or F: Rodents and Mammals have PARs

Answer 22

F, it is not necessary for them.