Bio 112 Chapter 11 Flashcards

A set of 100 flashcards covering the process of meiosis, phases of meiotic division, genetic variation, and types of sexual life cycles as described in the lecture notes.

How many gametes are required for sexual reproduction according to the lecture?

$2$ gametes

What is the resulting cell called when two gametes join during fertilization?

A zygote (fertilized egg)

How many sets of chromosomes are contained within a haploid cell?

$1$ set

How many sets of chromosomes are contained within a diploid cell?

$2$ sets

What is the specific requirement for sexual reproduction regarding the number of chromosome sets?

It requires nuclear division that splits the number of chromosome sets in half.

What identifies somatic cells in multicellular organisms?

They are all cells that are not gametes or reproductive cells.

What does the abbreviation "HC" stand for in these notes?

Homologous Chromosomes

In somatic cells, what are the matched pairs of chromosomes that have the same genes at the same locations?

Homologous Chromosomes ($HC$)

Where does a diploid organism receive each copy of its homologous chromosomes?

$1$ copy from each parent

How is meiosis defined in the context of nuclear division?

The formation of haploid cells from diploid cells.

How do daughter cell nuclei in mitosis compare to their parent nuclei?

They are identical.

What is the ploidy level of the parent nuclei and daughter nuclei in meiosis?

Parent nuclei are diploid and daughter nuclei are haploid.

What are the two main stages of meiotic division?

Meiosis $I$ and Meiosis $II$

What phase precedes Meiosis $I$?

Interphase

What occurs during the $G_1$ phase of interphase?

Cell growth

What specific event takes place during the $S$ phase of interphase?

Chromosomal $DNA$ replication

What are the two identical copies of replicated chromosomes called?

Sister chromatids

What proteins hold sister chromatids together at the centromere until anaphase $II$?

Cohesion proteins

What is the purpose of the $G_2$ phase of interphase?

Final preparations for meiosis

In Prophase $I$, where are homologous chromosomes attached to the nuclear envelope?

At their tips

What is the synaptonemal complex?

A lattice of proteins that forms between homologous chromosomes.

What process does the synaptonemal complex support?

Crossing over

What is the definition of "crossing over"?

The exchange of chromosomal segments between homologous nonsister chromatids.

What is the first source of genetic variation in nuclei produced via meiosis?

Crossing over

What is the term for the tight pairing of homologous chromosomes during prophase $I$?

Synapsis

How are genes aligned during synapsis?

Chromatid genes are precisely lined up with one another.

What happens to the synaptonemal complex after synapsis is complete?

It begins breaking down.

What are chiasmata?

$X$-shaped crossover sections between non-sister chromatids of homologous chromosomes.

Until which phase do chiasmata remain attached?

Anaphase $I$

What is the minimum number of chiasm per chromosome required for proper separation of HCs in meiosis $I$?

$1$ chiasma

What are the pairs of homologous chromosomes called at the end of prophase $I$ when they are held together only by chiasmata?

Tetrads

Between which structures is $DNA$ exchanged during a crossover event?

Between maternal and paternal chromosomes (homologous nonsister chromatids).

What is contained in a recombinant sister chromatid?

$DNA$ from both parents

What is the key event that occurs during Prometaphase $I$?

Spindle fiber microtubules attach to kinetochore proteins at centromeres.

What are kinetochores?

Multiprotein complexes responsible for the binding of centromeres to microtubules.

How are the members of a homologous pair attached to microtubules during prometaphase $I$?

Each member is attached to a microtubule from opposite poles of the cell.

At the end of Prometaphase $I$, each tetrad is attached to microtubules from both poles; how is each HC oriented?

$1$ homologous chromosome faces each pole.

What structure is completely broken down by the end of Prometaphase $I$?

The nuclear membrane

Where are homologous chromosomes arranged during Metaphase $I$?

At the metaphase plate (midline of the cell).

Besides crossing over, what other event in Metaphase $I$ is highly responsible for genetic variation?

The random position of the homologous pairs.

What happens during Anaphase $I$?

Microtubules pull chromosomes apart.

Do sister chromatids separate during Anaphase $I$?

No, they remain tightly connected at the centromere.

What specific structures are broken during Anaphase $I$ to allow chromosomes to move apart?

Chiasmata

Where are the separated chromosomes located during Telophase $I$ and Cytokinesis?

At opposite poles

What structure is used in almost all animals and fungi to split the cell during cytokinesis?

A cleavage furrow (constricted actin ring).

How does cytokinesis differ in plants compared to animals?

In plants, a cell plate is formed at the metaphase plate which develops into cell walls.

How many cells are produced from the division of a diploid cell in Meiosis $I$?

$2$ haploid cells

Why are the cells after Meiosis $I$ considered haploid even though sister chromatids are still present?

Because there is only one of each pair of the homologous chromosomes at each pole.

How many full sets of chromosomes are present in a cell at the end of Meiosis $I$?

$1$ single full set

What is the name of the short interphase that some species enter prior to Meiosis $II$?

Interkinesis

What phase is specifically lacking in interkinesis?

The $S$ phase ($DNA$ duplication).

What happens to the sister chromatids of the two daughter cells during Meiosis $II$?

They separate to form $4$ new haploid gametes.

What happens to chromosomes in Prophase $II$ if they decondensed in Telophase $I$?

They condense once more.

What happens to duplicated MTOCs during Prophase $II$?

They move apart towards opposite poles.

What event characterizes Prometaphase $II$?

Complete breakdown of nuclear envelopes and full formation of the spindle.

In Prometaphase $II$, how are sister chromatids attached to microtubules?

To microtubules from opposite poles via individual kinetochores.

Where are sister chromatids aligned during Metaphase $II$?

At the cellular equator

What is the state of sister chromatids during Metaphase $II$?

They have reached maximum condensation.

What pulls sister chromatids apart during Anaphase $II$?

Kinetochore microtubules

What is the role of nonkinetochore microtubules during Anaphase $II$?

The elongation of the cell

What happens to chromosomes once they arrive at opposite poles in Telophase $II$?

Decondensation of chromosomes

What forms around the chromosomes during Telophase $II$?

New nuclear envelopes

What is the final result of cytokinesis after Meiosis $II$ starting from a single diploid parent?

The formation of $4$ unique haploid cells.

Are the cells produced at the end of Meiosis $II$ genetically identical?

No, they are genetically unique.

How many nuclear divisions occur in mitosis?

$1$ single nuclear division

What is the genetic relationship between the two nuclei partitioned in mitosis and the original nucleus?

They are genetically identical.

In mitosis, how many sets of chromosomes are in the daughter cells compared to the parent?

The same number of sets

In mitotic division, where do the single set of duplicated chromosomes align?

On the metaphase plate

What is the only reason the products of meiosis $II$ are not identical like mitosis?

Crossover

Why is mitosis not considered a reduction division?

Because there is still a single set of chromosomes, just as in the start of the division.

How many nuclear divisions occur in meiosis?

$2$ nuclear divisions

How many nuclei are produced at the end of meiosis?

$4$ nuclei

How does the chromosome count in meiosis daughter nuclei compare to the original diploid cell?

They contain only half (a single chromosome set).

In which stage of meiosis do the primary differences from mitosis occur?

Meiosis $I$

Why is Meiosis $I$ referred to as a reductional division?

Because the number of chromosome sets is reduced from $2$ to $1$.

When is sexual reproduction believed to have appeared in evolutionary history?

Likely as an "evolutionary innovation" after the appearance of eukaryotic cells.

What are two cited advantages of asexual reproduction?

Speed of reproduction and only needing one organism.

Under what condition is it advantageous to produce identical offspring via asexual reproduction?

If the parent is succeeding in a particular habitat.

What is a major explanation for why sexual reproduction is common in multicellular organisms despite the overhead?

Genetic variation and diversity are important for survival and reproduction.

What can happen to mutations during sexual reproduction?

They can be "reshuffled" from generation to generation.

What is defined as the alternating of fertilization and meiosis?

Sexual Life Cycles

How is fertilization defined in the lecture?

The joining of $2$ haploid gametes and the restoration of the diploid condition.

What life-cycle type do most animals use?

Diploid-dominant life-cycle

In a diploid-dominant cycle, what are the only haploid cells produced?

Gametes

What are germ cells?

Specialized diploid cells produced in the gonads.

What cell type is capable of both mitosis (for the cell line) and meiosis (for gametes)?

Germ cells

Can haploid gametes in a diploid-dominant life cycle divide again?

No

Which organisms have an obvious multicellular haploid stage?

Fungi and some algae

In the life cycle of fungi, what is the ploidy of the main body?

Haploid

How are haploid cells formed in fungi?

By mitosis

What is formed when special haploid cells from two individuals combine in fungi?

A diploid zygote

What does the diploid zygote in fungi produce through meiosis?

$4$ haploid cells called spores

What life-cycle pattern is found in plants and some algae?

Alternation of generations

What defines "alternation of generations"?

Having both multicellular diploid and haploid life stages.

What are gametophytes?

Haploid multicellular plants

Is meiosis directly involved in gamete production in gametophytes?

No, gametes are produced from specialized cells.

What results from fertilization between gametes in the plant life cycle?

A diploid zygote

What does the plant zygote become after several rounds of mitosis?

A multicellular diploid plant called a sporophyte.

What is a sporophyte?

A multicellular diploid plant.

What do special cells in the sporophyte produce through meiosis?

Haploid spores