bio 9th ch 10 meiosis

gametes

cells that contain half the number of chromosomes of a somatic cell.

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germline cell

cells that produce gametes

• ovary
• testes

gonads

organs (not organ systems) that produce gametes using germline cells (ovary and testes)

meiosis

• produces 4 daughter cells
• each with have half the number of chromosomes of the original parent cell
• 2 nuclear divisions

prophase 1

appearance of chromosomes, homologous chromosomes synapse, and are crossing over between non-sister chromatids of homologous chromosomes may occur

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metaphase 1

homologous pairs of chromosomes line up independently at the spindle equator

anaphase 1

homologous chromosomes are seperate and move towards opposite poles

telophase 1

chromosomes disappear. Nuclear membranes reform and the cell divides into two; each daughter cell has half the number of chromosomes as a parent

prophase 2

chromosomes reappear in each cell. each chromosome exist as two sister chromatids joined at the centromere.

metaphase 2

each chromosome lines up at the spindle equator

anaphase 2

centromeres are split and sister chromatids move to opposite poles.

telophase 2

chromosomes disappear. nuclear membranes reform and the cell divides into two.

increasing genetic variation

• to produce gametes that are genetically distinct from each other
• things that increase genetic diversity are: crossing over, independent assortment

chiasma/ chiasmata

• where the chromatids overlap
• prophase 1

crossing over

• when sections of the chromatids detach and rejoin. this results in genetic variation, exchanging of DNA which make the offspring genetically different to the parent.
• prophase 1

Recombinants

• the chromosomes that have crossed over.
• prophase 1

independent assortment

the random orientation of homologous chromosomes along the metaphase plate during metaphase 1

Anaphase

is the stage of mitosis/meiosis where the sister chromatids separate and are pulled towards opposite poles of the cell by the spindle fibers.

Chromosome

A __ is a long, coiled-up strand of DNA that contains genes and other genetic information.

Throughout most of a cell’s life cycle, the DNA is unraveled. The DNA only condenses into ___ during cell division.

Crossover

a process in which homologous chromosomes pair up and exchange genetic material.

occurs during the prophase I stage of meiosis. 

Cytokinesis

a stage during mitosis or meiosis where the cytoplasm is divided, creating two daughter cells from one parent cell.

Diploid

a cell containing two complete sets of chromosomes, one from each parent.

The body, or somatic, cells of an organism (all cells other than the germ cells) are _.

DNA

is a molecule that contains the genetic instructions used in the development and function of all living organisms. It is composed of nucleotides that are arranged in a double helix structure.

Dominant

a trait that is always expressed when it is present.

_ alleles are usually represented by capital letters, such as F

Gamete

a mature, haploid reproductive cell that is created as a result of meiosis.

• Male cells that undergo meiosis produce _ called sperm cells.
• Female cells that undergo meiosis produce polar bodies and called egg cells (ova)

Genotype

The genetic makeup of an organism

The __ of an organism refers to its complete set of inherited genes that determine its physical and behavioral traits.

Germ cell

a sexual reproductive cell that has the potential to develop into gametes.

cells include gametes as well as the diploid cells that divide to produce gametes

Haploid

a cell containing a single set of unpaired chromosomes. 

cells contain half the number of chromosomes as diploid cells. The gametes (sperm and egg cells) of an organism are _.

Homologous chromosomes

a pair of chromosomes that are similar in length as well as gene and centromere position

Interphase

a phase in a cell’s life cycle where it grows, replicates DNA, and prepares for cell division

Meiosis

a type of cell division in which a parent cell divides twice, producing four daughter cells. 

During _, DNA is replicated only once, resulting in four daughter cells with half the amount of genetic material (haploid) as the parent (diploid)

Metaphase

a stage during mitosis and meiosis in which the chromosomes line up along the metaphase plate and chromosomes attach to spindle fibers

Mitosis

a type of cell division in which a parent cell divides once, producing two daughter cells. 

During _, the DNA is replicated once, resulting in two daughter cells that have exact copies of the parent cell’s DNA

Ovum

(egg cell) – a female germ cell involved in reproduction. 

An _ can grow into an organism after it is fertilized by a sperm cell.

Phenotype

the physical appearance of an organism.

Organisms with different genotypes can have the same __. For example, an RR fruit fly and an Rr fruit fly both will have red eyes.

Prophase

a stage during mitosis and meiosis in which the nuclear envelope breaks down, the chromosomes condense, and centrosomes move to opposite poles of the cell.

Recessive

a trait that is not expressed when the dominant allele is present.

__ alleles are usually represented by lowercase letters, such as f

Sister chromatids

two identical strands of DNA in a chromosome connected by a centromere

Sperm cell

a male germ cell involved in reproduction.

• Immature spermatids develop into cells. 
• _ cells can fertilize egg cells during reproduction

Telophase

a stage during mitosis and meiosis in which the DNA unwinds and the nuclear envelope reforms around the chromosomes or chromatids

Zygote

a fertilized cell that forms from the fusion of an egg cell and a sperm cell

Human cells with 46 chromosomes actually contain 23 pairs of

Homologous chromosomes

In meiosis, the original number or chromosomes (46 in humans) is restored after:

Fertilization

Homologous chromosomes

A pair of chromosomes with 1 chromosome provided by the maternal side (female parent) and 1 chromosome provided by the paternal side (male parent).
These have identical gene loci and identical centromere positions.

In what phase of mitosis are chromosomes not visible through the microscope?
Why is this?

Interphase.
Because genetic information isn't in the form of chromosomes, it's chromatin (resemble little spaghetti strings through the microscope)

What happens to a cell immediately after cell division?

It enters the G1 phase of interphase

What happens during the G1 phase of interphase?

A cell grows and performs all its routine metabolic functions (duplication of organelles, protein synthesis, etc.)

Why might a cell enter the G0 phase even if it has undergone many divisions and is able to, theoretically, go undergo another?

They may have reached maturity (ex. mature nerve cell), or they are simply destined to never divide again.

What happens during the S phase of interphase?

DNA replication (copying).
The helical molecule of DNA partially uncoils and the two strands separate at the point where the hydrogen bonds connect the nitrogen base pairs.
Each exposed base pair of the old DNA strand then pairs with a complementary base of a newly synthesized nucleotide and the hydrogen bond re-forms.

What does a nucleotide of DNA consist of?

A deoxyribose sugar bound to a phosphate group, and to one of four nitrogenous bases (adenine, thymine, guanine, cytosine).

What is each arm/leg of a replicated chromosome called?

A chromatid (or sister chromatids).

What region holds sister chromatids together?

The centromere

At what stage of interphase does a cell commit to undergoing mitosis?

The S (synthesis) phase

What happens during the G2 phase of interphase?

The cell prepares for actual division. There may be some additional growth as well as an accumulation of energy reserves, and synthesis of enzymes and other proteins.

Where is the centrosome located?

Directly outside the nuclear membrane

What is the centrosome?

A subcellular region which functions through the cell cycle to organize the cell's microtubules forming the spindle apparatus.

What makes up a centrosome?

Pericentriolar material (complexes composed of tubulin protein) and a pair of structures known as centrioles.

What makes up the centriole pair?

2 cylindrical bodies (also composed of microtubules) which lie at right angles to each other.

What happens to centrosomes during interphase?

The single centrosome duplicates, forming two centrosomes which remain together near the nucleus.
(Not visible through a compound microscope).

What is a kinetochore microtubule?

A microtubule that grabs chromosomes in order to pull them towards each pole of the cell (towards the centrosomes).

What is a non-kinetochore microtubule?

A microtubule that does not grab onto a chromosome, but rather reaches to the opposite pole of the cell and push away, causing the cell to grow and eventually separate (cytokinesis)

What is the role of astral rays?
Where are they found in a cell?

Their role is to anchor centrioles to poles.
They're found around the centrioles.

Mitosis vs. cytokinesis

Mitosis: The division of the nucleus.
Cytokinesis: The division of the cell itself (division of the cytoplasm).

Important steps for prophase

• Chromosomes coil and shorten, becoming visible on the compound microscope.
• The mitotic spindle begins forming.
• Asters extend from each centrosome towards the plasma membrane.

What is an aster?

A radial array of short microtubules

At the outside of each centromere is a protein complex known as a:

Kinetochore

What marks the end of prophase?

The disappearance of the nuclear membrane and the nucleolus

Important steps for metaphase

• The duplicated chromosomes line up along the metaphase plate.
• The arms of chromatids extend freely in any direction in the cytoplasm.
• For each chromosome, the kinetochore region attaches to kinetochore microtubules coming from opposite poles.

Important steps for anaphase

• Centromere of each chromatid pair splits, and the chromatids separate.
• Each chromatid is now a separate and functional daughter chromosome.
• Centromere (of each daughter chromosome) is pulled to opposite poles of the cell as kinetochore microtubules shorten.
• The cell elongates.

What is the end of anaphase marked by?

When each daughter chromosome has arrived to their respective poles.

How does a cell elongate (particularly during anaphase?

By non-kinetochore microtubules pushing away from their opposite pole.

Important steps for telophase

• A new nuclear membrane is assembled around each two groups of daughter chromosomes.
• Nucleoli is reformed.
• Chromosomes gradually uncoil and lengthen (returning to the form of chromatin).

What is the end of telophase marked by?

The end of the division of the cytoplasm (cytokinesis).

How does cytokinesis occur in animal cells?

With the aid of a cleavage furrow ("pinching in")

What is used to form the cleavage furrow of an animal cell (during telophase)?

Actin microfilaments forming a contractile ring.

What is a blastula?

An embryological stage in the development of most animals.

Where in the body does meiosis occur?

In the gonads (ovaries and testes)

How is genetic variability introduced in meiosis?

• Independent assortment
• Crossing-over

Sister chromatids are held together at the:

Centromere

Unique features of prophase I

• Pairing of homologous chromosomes
• Synapsis (via tetrads)
• Crossing-over

What are homologous chromosomes?

The same numbered chromosome finding its pair.
Ex. Chromosome 1 (paternal) pairs with chromosome 1 (maternal).

What is synapsis?
What does this form?

Homologous chromosomes pair up side-by-side.
This forms a tetrad.

When does crossing-over occur?

During prophase I when homologous chromosomes have formed tetrads.

During meiosis, how long do homologous chromosome pairs stay together?

Throughout late prophase I and metaphase I.

When does independent assortment occur?

Metaphase I

What does "independent assortment" mean?

Tetrads line up on the metaphase plate randomly (all maternal chromosomes could even be on one side or vice versa).

True or False:
DNA replication occurs in interkinesis because it is identical to interphase.

False.
Each chromosome is still comprised of two sister chromatids.

True or False:
Chromosomes coil and condense during prophase II.

True.
Chromosomes have uncoiled during telophase I and must re-condense.

What is the role of mitosis in the body?

• Growth
• Repair of old/damaged cells

What's the function of meiosis in the human body?

• Producing sex cells
• Passing of genes with genetic information

Interkinesis vs. interphase

During interkinesis, there is no replication of DNA

Prophase of mitosis vs. prophase II of meiosis

• Mitosis: No pairing of homologous chromosomes
• Mitosis: No synapsis, recombination, or crossing-over

Anaphase of mitosis vs. anaphase I of meiosis

• Mitosis: Sister chromatids are being separated.
• Meiosis (I): Chromosomes are being separated from their tetrads/homologous pairs.

Synapsis vs. crossing-over

• Synapsis: Pairing of homologous chromosomes (prophase I).-
• Crossing-over: Exchange of genetic material between tetrads/homologous pairs (during synapsis).

What are homologous chromosomes?

Homologous chromosomes are pairs of chromosomes, one inherited from each parent, that have the same genes at the same loci, but may have different alleles.

What are sister chromatids?

Sister chromatids are identical copies of a chromosome connected by a centromere, formed during DNA replication.

What is Independent Assortment?

Independent Assortment is the process by which the different genes independently separate from one another when reproductive cells develop.

What is a genome?

A genome is the complete set of genes or genetic material present in a cell or organism.

What is crossing over?

Crossing over is the exchange of genetic material between homologous chromosomes during prophase I of meiosis, leading to genetic diversity.

What is the difference between haploid and diploid?

Diploid cells contain two complete sets of chromosomes (2n), one from each parent, while haploid cells contain one complete set of chromosomes (n).