Biology Test 7: Mitosis & Meiosis

Cell division

is the process by which cells reproduce; all cells come from preexisting cells

Genes

Cellular information is contained in genes; genes code for proteins

the genes are separated into...

daughter cells

chromatin

thin uncoiled strands composed of DNA and protein

chromosome

rod shaped structures of DNA and protein (histones)

chromatid

two identical parts of a chromosome

centromere

point at which each pair of chromatids attach

histones

a special protein molecule that DNA wraps around during chromosome formation

Homologous Chromosome

one of two pair members of a morphologically similar chromosomes

Diploid

a cell that contains both chromosomes of a homologous pair

Haploid

A cell that only has one chromosome of each homologous pair

2N refers to a...

diploid cell

1N refers to a...

haploid cell

Cell Cycle

the sequence of five events of cell division: includes 3 phases of interphase, mitosis, and cytokinesis

Interphase

period of cell growth and development that proceeds mitosis; 3 phases of Interphase

Interphase G1

Cell doubles in size, Enzymes and organelles roughly double in number

Interphase s

DNA that makes up chromatin replicates

Interphase G2

cell undergoes rapid growth to prepare for mitosis, Synthesizes necessary enzymes and structures

Mitosis

division of the cell nucleus in which the chromosomes of the parent cell divide into two identical sets; 4 phases of Mitosis

Prophase

first stage of mitosis; 3 steps

Early Prophase

Chromatin coils and forms chromosomes, Nuclear membrane and nucleolus break down and disappear, Centrioles move to opposite poles of the cell

Middle Prophase

Development of spindle fibers; polar and kinetochore fibers

Polar fibers

from centriole to centriole

Kinetochore fibers

from centromere to centrioles

Final Prophase

Asters are formed

Asters

protein fibers that radiate from each centriole

Metaphase

second stage of mitosis, during which all the chromosomes move to the cell's equator

Anaphase

stage of mitosis where the chromosomes separate; no chromosomes left, only chromatids

Telophase

final stage of mitosis; there are two identical sets of chromatids at each pole, centrioles and spindle fibers break down, chromatids elongate and unwind into chromatin, nuclear membrane forms and nucleolus appears

Cytokinesis

the division of the cytoplasm of a parent cell and its contents into two daughter cells; left with two new cells, different in plant cells

Cytokinesis in plant cells

the golgi bodies fuse at the equator to form a cell plate

cell plate

membrane across the middle of a plant cell

Meiosis

the process of nuclear division that reduces the number of chromosomes by half; Unlike mitosis which deals with body cells, meiosis deals with sex cells

Meiosis I

-the first division; homologous chromosomes are separated into separate cells
-Follows interphase, just like mitosis
Prophase I
Metaphase I
Anaphase I
Telophase I

Prophase I

Spindle appears
Tetrads of homologous chromosomes form
As tetrads form, portions of chromatids are
exchanged = crossing over
Results in exchange of genes

Synapsis

pairing of homologous chromosomes

Tetrad

group of two chromosomes, the tetra "four" refers to the amount of chromatids

Metaphase I

Tetrads move to the equator of the cell
Moved by spindle fibers
homologous chromosomes stay together

Anaphase I

Homologous pairs of chromosomes separate
Each chromosome is still composed of 2 chromatids and a centromere

Telophase I

Cytoplasm divides forming two daughter cells

Meiosis II

-occurs in each cell formed during meiosis I. (NOT preceded by DNA replication)
-the second division; chromatids of each chromosome are separated into separate cells
-Each cell will have one half the number of chromosomes as the parent cell
Prophase II
Metaphase II
Anaphase II
Telophase II

Prophase II

Chromosomes coil again
New spindle fibers form

Metaphase II

Chromosomes are lined up on the equator of the cell
Each chromosome is made of 2 chromatids attached at a centromere
Spindle fibers attach to centromeres

Anaphase II

Centromeres divide
Spindle fibers pull each chromatid to the opposite poles

Telophase II

Spindle fibers dissolve
Nuclear membrane forms
Cells begin to divide
Do not fully divide until cytokinesis occurs

Gametes

sexual reproductive cells
Male gametes = sperm
Female gametes = egg

Ootid

egg cell = receives almost all of the cytoplasm

Polar bodies

three other cells = receive very little or no cytoplasm and eventually disintegrate

Asexual Reproduction

production of offspring from one parent
No union of gametes

Sexual Reproduction

production of offspring through meiosis and fusion of gametes.
Offspring are genetically different than both parents

Genetic recombination

results from crossing over and homologous pairs of chromosomes separate independently
Introduces variation
Survival Advantage

Cell cycle is controlled

proteins called cyclins and a set of enzymes that attach to the cyclins and become activated

Cancer

uncontrolled cell division that may be caused by environmental factors or changes in enzyme production
Failure to produce enzymes, overproduction of enzymes, production of enzymes at the wrong time

Cancerous Cells form masses called

tumors; Malignant & Benign

Causes of Cancer because of genetic
factors are

Breast Cancer is more common in US than Japan
Stomach Cancer is more common in Japan than US

Causes of Cancer because of Environmental Factors

Cigarette smoke
Air & water pollution
UV radiation
Viral infections that damage genes

Cancer Prevention

Healthy Lifestyle
Diets low in fat and high in fiber
Intake of vitamins: A, C, E, and calcium
Daily Exercise
Not using tobacco