Biology Unit 7: The Cell Cycle and Genetic Variation

Interphase

the period of growth between cell divisions

G1

growing and developing, normal functions, proteins needed for DNA replication are made, some organelles are replicated, DNA is present in nucleus as chromatin - loose DNA

G0

normal processes, NOT preparing to divide or contributing in any way to divide, some cells are permanently in the phase

Synthesis

DNA replication occurs, an exact copy of DNA is made

G2

cell grows, normal functions, makes additional protein and organelles (if damaged), can't be repaired - apoptosis

Mitosis

divide cells into two daughter cells

Prophase

chromosomes shorten, thicken and become visible, nuclear membrane breaks down, a spindle begins to form, centrioles in animal cells help to organize the spindle fibers

Metaphase

chromosomes line up at center of cell, spindle fibers connect the centromere of each chromosome to the spindle

Anaphase

centromeres split and the sister chromatids split, a complete set of chromosomes move to opposite sides of the cell

Telophase

chromosomes decondense into chromatin, nuclear membranes reform, spindle breaks apart, opposite of prophase

Cytokinesis

completes cell division by splitting one cell into two daughter cells, animal cell - cell membrane draws inward, plant cell - a cell plate develops that becomes two membranes and a cell wall forms between them

Checkpoints

if one is not met, the cell will go under programmed cell death, or apoptosis

G1 Checkpoint

Is the cell large enough? Are sufficient nutrition available? Are growth factors present?

G2 Checkpoint

Was DNA replicated? Is the cell large enough?

Metaphase Checkpoint

Are all the chromosomes attached to microtubules?

Chromosomes

interphase, DNA and proteins, condensed at beginning of mitosis, comes in pairs

Chromatin

interphase, a complex of DNA and proteins that forms chromosomes within the nucleus of eukaryotic cells - decondensed or spread out

Chromatids

synthesis, threadlike, condensed DNA and proteins that form chromosomes within the nucleus of eukaryotic cells arms

Homologous Chromosomes

prophase I of meiosis, one set of maternal and paternal chromosomes

Relationship between mitosis and cancer

Mitosis is the process of cell division, and uncontrolled mitosis can lead to cancer.

Cancer

Occurs when mutated cells ignore or override the normal 'checkpoints' regulating mitosis and begin to reproduce unexpectedly.

Meiosis

Creates the gametes needed for sexual reproduction.

Gametes

Reproductive cells, sperm and egg.

Location of Gametes

Reproductive organs.

Males

Testes.

Females

Ovaries.

Haploid

Gametes have half the number of chromosomes found in a diploid body cell, 23 chromosomes.

Fertilization

Each haploid gamete contributes half the DNA of the new offspring.

Zygote

Single DIPLOID cell formed as a result of fertilization.

Asexual Reproduction

Involves a single parent dividing to produce offspring that are genetically identical.

Sexual Reproduction

Involves two parents contributing genetic material, resulting in offspring with unique genetic combinations.

Mitosis

Produces two diploid daughter cells that are genetically identical to the parent cell.

Meiosis

Produces four haploid daughter cells which are not genetically identical to the parent cell.

Meiosis I

Almost the exact same as mitosis.

Prophase I

Chromosomes condense, nuclear envelope breaks down, crossing over occurs, tetrad - group of 4 chromosomes.

Metaphase I

Pairs of homologous chromosomes move to center of cell, tetrads line up.

Anaphase I

Homologous chromosomes move to opposite sides of cell.

Telophase and Cytokinesis I

Chromosomes gather at sides of cell, cytoplasm divides, 2 cells are formed.

Meiosis II

Creates two new cells (now 4!!).

Prophase II

A new spindle forms around the chromosome.

Metaphase II

Chromosomes line up at center.

Anaphase II

Centromeres divide, chromatids move to opposite sides of cells.

Telophase and Cytokinesis II

Nuclear envelope forms around each set of chromosomes, cytoplasm divides - now 4 cells.

Crossing Over

Exchange of genetic material between homologous chromosomes during Prophase I of meiosis, creates recombinant chromosomes.

Independent Assortment

Homologous chromosomes line up randomly before distributing into daughter cells during Metaphase I of meiosis.

Random Fertilization

The random fusion of a sperm and egg cell at fertilization creates tremendous genetic variation.