BIO 221: Mitosis and Meiosis

Astral microtubules

project away from the center of the cell

Kinetochore microtubules

attach to kinetochore proteins in centromeres helping to position chromosomes for cell division

Polar microtubules

extend toward the opposite side/pole of the cell to seperate the chromatids during anaphase

Anaphase A

movement of chromosomes toward the poles

Anaphase B

spindle poles move apart

Cyotkinesis in animal cells

band of actin filaments retracted during cell divison which pinch off the animal cell breaking it in half (flexible)

Cytokinesis in plant cells

cell plate builds new section of cell wall which cuts the cell in half (rigid)

Results of mitosis

2 daughter cells with the same chromsome count and DNA content of the orginal cell (can occur in haploids and diploids)

What must occur before mitosis?

DNA replication

Centrioles

found in centromeres that must be replicated to ensure each daughter cell receives a complete chromosome set

What major events happen during prophase mitosis?

sister chromatids condense forming miotic spindles, the nuclear envelope begins to dissociate

What major events happen during prometaphase mitosis?

microtubules connect to chromatids fully forming the miotic spindle, nuclear envelope is gone

What major events occur during metaphase mitosis?

sister chromatids align along the metaphase plate for division and attach to both poles microtubules

What lines up the chromosomes during metaphase mitosis?

shortening and lengthening of kinetochore microtubules, along with spindle fibers

What major events occur during anaphase mitosis?

Sister chromatids are separated and pulled to opposite poles of the cell by the spindle fibers

What major events occur during telophase mitosis?

chromosomes deconsdense reforming the nuclear envelope leading to cytokinesis (cleavage furrow occurs here)

What major events occur during cytokinesis mitosis?

the cytoplasm splits into two daughter cells

Results of meiosis I

2 new haploid cells (not identical) with half the number of chromosomes

Results of meiosis II

four daughter cells each with one set of chromosomes

Results of meiosis

four haploid cells containing a single copy of the genome

What type of cells perform meiosis?

gametes

Genetic recombination in meiosis

the regrouping of genes in an offspring resulting in a genetic makeup that is differs from the parents

What must happen before meiosis?

interphase (G1, S, G2)

What occurs during prophase meiosis I?

homolougous chromosomes synapse forming bivalents (crossing over) and then condense degrading the nuclear envelope

Homologous chromosomes

Pair of chromosomes that are the same

Synapsis

Pairing of homologous chromosomes

Synaptomnemal complex

brings homologous chromsomes together which facilitates genetic recombination

Bivalent

paired up homologous chromosomes

Crossing over

process in which homologous chromosomes exchange portions of their chromatids during meiosis

Chiasma

site of crossing over

What occurs during prometaphase meiosis I?

nuclear envelope dissociates into vesicles and bivalents become attached to minetochore microtubules

What occurs during metaphase meiosis I?

bivalents align along the metaphase plate with each chromtid attached to only one pole

What occurs during anaphase meiosis I?

homologous chromsomes seprate (X becomes two lines) pulled toward opposite poles as kinetochore microtubules shorten and polar microtubules lengthen

What occurs during telophase/cytokinesis meiosis I?

chromosomes decondense reforming the nuclear envelope, cell seperation occurs (2 haploid daughter cells)

Interkinesis

Period of time between meiosis I and meiosis II during which no DNA replication takes place

What events differ between meiosis I and II?

everything that happened in meiosis I occurs again

Why is meiosis necessary?

to prevent DNA content and chromosomal count doubling with each generation

What happens during fertilization?

2 haploid gametes join together to form a diploid zygote

Diploid dominant sexual reproduction

a dominant diploid stage in the life cycle with only haploid cells being gametes

Haploid dominant sexual reproduction

a dominant haploid stage with a temporary diploid stage (single-celled zygote)

Alternation of generations sexual reproduction

cycle between two distinct multicellular phases (haploid gametophyte produces haploid gametes and diploid sporophyte produces haploid spores)

Metacentric

centromere in middle

Submetacentric

centromere slightly off center

Acrocentric

centromere close to end

Telocentric

centromere at end

Chromosome deletion

deletion of a chromosome segment

Chromosome duplication

mutation that doubles a segment of a chromosome

Chromosome inversion

flip a segment of chromosome (DE to ED)

Simple translocation

remove a segment of a chromosome and input another in its place

Reciprocal translocation

two-way exchange of segments between the chromosomes

Euploid

normal number of chromosomes

Haploid

one complete set of chromosomes

Diploid

two complete sets of chromosomes

Triploid

three complete sets of chromosomes

Tetraploid

four complete sets of chromosomes

Aneuploid

abnormal number of chromosomes (too many or too little)

How does aneuploid occur?

nondisjunction of chromosomes during meiosis I or II

What are the possible results of aneuploid?

Down, Edward, Patau, Klinefelter, Jacobs, Triple X, or Turner syndrome