Reproduction

Chromatin ~ DNA coated in protective proteins.

Chromosome ~ Chromatin that has been copied and coiled up into an X shape to prepare for cell division.

DNA in the Nucleus

Parts of a chromosome:

• Histones

• Centromere

• Sister Chromatids

Sister Chromatids

Two complete copies of DNA joined at the centromere.

Copy is made by replication.

Homologues ~ Each sister chromatid contains the same genetic information.

Diploid ~ Describes a cell that has two of each kind of chromosome (homologous pairs). Normal body cells are diploid. 2n

Humans 2n = 46

Haploid ~ A cell that has one of each kind of chromosome. Gametes (sex cells) are haploid. N

Humans n = 23Homologous pairs ~ Chromosomes occur in pairs. Both chromosomes will carry similar information. One came from the father, the other came from the mother.

Types of Reproduction

AsexualProduces somatic cells (body cells)Produces diploid cellsMakes clonesCells are made by

SexualProduces gametes (sex cells)Produces haploid cellsMakes offspring that are genetically different from the

parents.Cells are made by

Asexual Reproduction ~ Reproduction that does not require the exchange of DNA. There is only one parent, and the offspring will be clones (have the same DNA) of the parent.

1. Fragmentation

2. Budding

3. Spores

Mitosis Terms

Parent cellSpindleDaughter cell

The Cell Life Cycle:1. Interphase

2. Mitosis

• Prophase

• Metaphase

• Anaphase

• Telophase

3. CytokinesisOnion cells in

interphase

Interphase: The “living” stage.

Interphase: A cell is carrying out normal functions for homeostasis. At the end, replication of DNA occurs, and the cell is called a “Mother” cell.

Onion cells in interphase.

Prophase:• Nuclear Membrane

Dissolves

• Chromatin coils up into chromosomes

• Centrioles move to opposite sides of cell and form spindle

Onion Cell in Prophase: Note that the nuclear material is spreading out, due to the dissolution of the nuclear membrane.

Prophase: The 1st phase of Mitosis

Metaphase:

Chromosomes line up on center of spindle.

Onion cell in metaphase: The chromosomes are gathered in the middle

Metaphase: 2nd Phase of Mitosis

Anaphase: 3rd Stage in Mitosis

Anaphase: The chromosomes split into separate sister chromatids, and move to opposite centrioles

Onion Cell in anaphase: Each chromatid is dragged to opposite sides.

Telophase: Last stage of Mitosis

Telophase:

• Two new nuclear membranes form.

• Spindle dissolves.

• Chromatids uncoil into chromatin.

Onion Cell in telophase: The chromosomes are in 2 separate nuclei in the same cell.

Cytokinesis: Cell splits into two daughter cells.

Cytokinesis (fission): After two nuclei have formed, the mother cell divides to form 2 daughter cells.

Fish cells undergoing cytokinesis

Daughter cells of onion

Differences in Plant and Animal Cell Mitosis

Plant CellsNo centriolesFormation of cell

plate in telophase

Animal CellsCentrioles form

spindleCleavage furrow

develops in telophase

Sexual Reproduction ~ Reproduction that requires the exchange of DNA between two members of the same species. The offspring will have DNA that combines genes from both parents, but will be unique to the offspring.

1. Haploid

2. Gametes

3. Sperm

4. Ovum

Meiosis

Two divisions, no replication of DNA in between.Chromosomes will exchange pieces to ensure

genetic diversity of offspring.Resulting cells will be haploid gametes.

Meiosis ~ Process by which haploid cells are produced.

Spermatogenesis ~ Meiosis that produces four new sperm cells from one mother cell.

Oogenesis ~ Meiosis that produces one new ovum from one mother cell.

Meiosis I

Prophase I ~ Same events as in prophase of mitosis, except:Crossing over ~ Pairs exchange pieces with each

other. Chiasmata ~ Sites on chromosomes where crossing

over occurs.Metaphase I ~ Homologous pairs line up on

metaphase plate. Centromeres of each are attached to separate centrioles.

Anaphase I/Telophase I ~ Pairs separate, and intact chromosomes are pulled to opposite poles. Spindle dissolves, new nuclear membranes form. Cell divides.

Meiosis II

Prophase II ~ (No DNA duplication has occurred!) New spindle forms, nuclear membrane dissolves.

Metaphase II ~ Chromosomes line up.Anaphase II ~ Centromeres break, daughter

chromosomes move to opposite sides. Telophase II ~ Same as mitosis. Cells are

haploid.Spermatogenesis ~ 4 viable daughter cells.Oogenesis ~ 3 commit apoptosis, only one continues.

Cell Development

Fertilization

Zygote

Embryo

Cell differentiation ~ Process in which a developing cell is specialized. Genes are selectively “turned off” to determine the cell type.