Honors Bio: Reproduction of Cells and Organisms Pt. 1 (cell cycle, mitosis, meiosis)

Cell Cycle

life span or generation time of a cell from its beginnings, through its growth and to the time when it will divide

Life span varies according to cell type

Bacteria - 15 mins

Cheek Cells - hours

Stomach lining - days

Muscle cells - years

1st Growth (G1)

cell increases to adult size
performs its cell functions

G0

jumps out of cell cycle
will never divide again

Synthesis (S)

DNA replication
cell is committed to dividing

2nd Growth (G2)

build up materials needed for cell division before protein synthesis shuts down

Mitosis

“cell division”

a form of asexual reproduction where a parent cell divides producing two daughter cells having identical genetic components

occurs in somatic cells of multicellular organisms

Parent cell

original cell that divides producing daughter cells

Daughter Cells

produced by parent cell, have identical genetic components

Somatic Cells

normal body building cells

not involved in sexual reproduction

Purpose of Mitosis

Unicellular (and some multicellular) organisms: a form of asexual reproduction

Multicellular organisms: make the processes of growth, development and repair possible

What must multicellular and unicellular organisms pass on?

diploid number of chromosomes characteristic of that species

Human 2n=46

Fruit fly 2n=8

Diploid

full set/2n

IPMAT

Interphase (not included in mitosis)

Prophase

Metaphase

Anaphase

Telophase

Interphase

parent cell

G1 - growth from previous division

S - DNA replication

G2 - preparation for division

Prophase

old cytoskeleton breaks down

centrioles separate, replicate and migrate to opposite poles and build aster rays

nuclear membrane “flows” into ER

chromatin condenses into chromosomes

Prophase (in nucleus)

chromatin condenses to form chromosomes through a series of coiling and foiling processes

Chromatin

combination of DNA and histones

Chromosomes

colored bodies

Sister chromatids

replicated copies of DNA held together by a centromere

Centromere

constricted region on a chromosome where sister chromatids are joined

Aster Rays

new cytoskeleton

Spindle apparatus

forms to separate sister chromatids

composed of aster rays, polar fibers, and kinetochore fibers

Polar fibers

spindle fibers that extend toward the midpoint of the cell

Kinetochore fibers

attached to centromere

Metaphase

spindle apparatus formed

chromosomes pulled to metaphase plate

Metaphase plate

imaginary line in the center of a dividing cell where all the chromosomes align

Anaphase

polar fibers lengthen pushing poles apart

kinetochore fibers shorten separating chromatids from each other producing sister chromosomes

Sister chromosomes

produced by kinetochore fibers shorting to separate chromatids from each other

Telophase

sister chromosomes reach opposite poles

nucleus begins to reform as polar and kinetochore fibers break down

cytokinesis begins with forming a cleavage furrow

Cleavage Furrow

ring of actin microfilaments pulling (in animals)

Cytokinesis

division of cytoplasm

Cell plate

the fusion of these vesicles forms new cell membranes between the two cells and cell wall is then deposited by each cell (in plants)

Which plant cells are restricted of division?

cells that have not formed a woody secondary cell wall (leaves, outer ring of stem/trunk, buds and root tips

Plant cells do not have centrioles or a cytoskeleton/aster rays but they do have…

cell wall which cannot be pinched in by a cleavage furrow

In plant cells…

spindle fibers break down and nucleus reforms

a cell plate forms by the migration and fusion of small vesicles that were produced during G2 phase of interphase

Meiosis

a process in which meiocytes found in gonads divide and reduce the diploid number of chromosomes to haploid producing gametes to be used in sexual reproduction

Meiocytes

special cells that only go through meiosis

Gonads

sex organs

Haploid

one half of diploid number

Gametes

sex cells

Gametogenesis

gametes transition into mature, functioning sex cells

Spermatogenesis

process in which male gametes mature into spermatogonia

Oogenesis

process in which female gametes mature into oocytes

Fertilization

union of the male and female gametes combining two sets of genetic material producing a zygote

Zygote

fertilized egg

Homologous chromosomes

matched pair of chromosomes that contain genes for the same “traits” located in the same positions on the pair

Paternal chromosomes

chromosomes from dad

Maternal chromosomes

chromosomes from mom

Meiosis 1

separation of homologous chromosomes

Synapsis

during prometaphase chromosomes pair up with their homologous partner forming a tetrad, the pair of homologous chromosomes attach to the same spindle

Tetrad

bundle of four chromatids

Meiosis 2

separation of chromatids

Similarity between mitosis and meiosis 2

there is only one chromosome one each spindle fiber

the chromatids are separated

Spermatogonia/Oogonia

cells in your gonads that still do mitosis

Primary spermatocyte/oocyte

does first division
first male meioctye/first female meiocyte

Secondary spermatocyte/oocyte

does second division

second male meiocyte/second division female meiocyte

Spermatid

mature sperm

Spermatozoa

fully mature sperm

Ootid

immature egg

Ovum

mature egg that is released

Polar body

discards extra chromatid

Advantages of Meiosis and Sexual Reproduction

Maintains chromosome number that is characteristic for each species (avoids doubling of chromosomes that would occur with each generation)

Combination of genetic material from genetically different parents produces variety in offspring’s traits (may help dilute harmful recessive mutation)

Meiotic process itself can produce new combinations of genetic material (crossing over, independent assortment)

Speeds up evolutionary process (greater variety in offspring means greater chance of adaptive combinations of genes)

Crossing-over

chromatids of homologous chromosomes exchange segments during synapsis producing recombinants

Recombinants

chromosomes that have new combinations of genes not present in the parents

Independent Assortment

when paternal and maternal chromosomes are reshuffled into different combinations in the offspring

Interkinesis

brief resting period between the first and second divisions of meiosis (only some species)