cell cycle, mitosis ,and meiosis

the cell cycle

90% of the time interphase

-cell growth

-DNA Replication

-cell functions

10% of the time M phase

why is mitosis important?

allows cells to reproduce making exact identical copies of themselves

mitosis stages

interphase

DNA replicates each chromosome has 2 chromatids now

46 ,46 - 46 ,92

Prophase

• Chromatin condenses into visible chromosomes

• Nuclear membrane breaks down

• Centrioles move to opposite poles

• Spindle fibers form

Metaphase

• Chromosomes line up in the middle of the cell

• Spindle fibers attach to centromeres

Anaphase

• Sister chromatids are pulled apart

• Move to opposite poles

Telaphase

• Chromatids reach opposite ends

• Nuclear membranes reform

Cytokenisis

• Cytoplasm divides

• Forms 2 identical diploid daughter cells

independant assortment

Random alignment of homologous chromosomes in Metaphase I of meiosis that creates genetic variation in gametes.

what is crossing over

exchange of DNA segments between homologous chromosomes during Prophase I of Meiosis.

what is a homologous chromosome?

A pair of chromosomes—one maternal and one paternal—that carry the same genes at the same loci but may have different alleles.

what are recombinant chromosomes?

Recombinant chromosomes are chromosomes that contain a new mix of maternal and paternal DNA after crossing over during Prophase I of Meiosis.

explain prophase 1 in meosis

Prophase I

• Chromosomes condense

• Homologous chromosomes pair up (synapsis)

• Crossing over occurs → recombinant chromosomes form

• Nuclear membrane breaks down

• Spindle fibers form

explain metaphase 1 in meosis

Metaphase I

• Homologous chromosome pairs line up in the middle

• Independent assortment occurs (random alignment)

explain anaphase in meosis 1

Anaphase I

• Homologous chromosomes separate

• Sister chromatids stay together

explain telophase and cytokinesis in meiosis 1

Telophase I + Cytokinesis

• Cell splits into 2 haploid cells

• Chromosomes are still duplicated

explain prophase 2 in meiosis

Prophase II

• Spindle fibers reform

• Nuclear membrane breaks down (if it reformed)

Explain metaphase 2 in meiosis

Metaphase II

• Chromosomes line up individually in the middle

explain anaphase 2 in meiosis

Anaphase II

• Sister chromatids separate

explain telophase 2 in meiosis

Telophase II + Cytokinesis

• Nuclei reform

• Cell divides

what is the main purpose of meosis

production of gametes

what is a zygote?

A zygote is the fertilized egg formed when sperm + egg fuse during fertilization.

haploid sperm (n) + haploid egg (n) → diploid zygote (2n)

what is ploidy

number of sets of chromosomes

what are the parts of interphase in the cell cycle?

G1 phase - cell grows and does normal functions

S phase - DNA is copied

G2 phase - more growth and preparation for division

G0 phase - (resting phase) not prepared to divide

what are the cell cycle checkpoints?

G1 check point

is cell growing?

is DNA damaged?

enough nutrients and energy?

G2 checkpoint

was all DNA copied correctly?

is DNA damaged?

prepared for mitosis?

M checkpoint(happens during metaphase)

chromosomes in the middle?
spindle fibers attached?

what happens if checkpoints fail?

if cell cant be fixed

Apoptosis happens (cell self destructs)

what regulates the cell cycle

controlled by 2 protiens cyclin and Kinase

Cyclin bind to kinase -cyclin kinase complex - tells cell go into next phase -cylin destroyed - CDK turns off

then different Cyclin comes to start process again for cell to go into next phase

Example flow:

• G1 cyclin + CDK → pushes cell into S phase

• S cyclin + CDK → starts DNA replication

• G2/M cyclin + CDK → triggers mitosis

Ensures cell only moves when ready

prevents damaged cells from dividing

what is nondisjuntion

when chromosomes fail to seperate properly in meosis 1 In

Meiosis I, homologous chromosomes are supposed to separate.

• In Meiosis II, sister chromatids are supposed to separate.

• If they don't separate correctly → nondisjunction occurs.