Reproduction and the Cell Reproduction and the Cell CycleCycle

Reproduction

The creation of a new organism by one or more “parent” organisms

Reproduction – 2 categories

SEXUAL• Production of a new

organism through the fusion of gametes (sperm and egg), usually from two different parents.

• Almost all animals

• Almost all plants

• Most fungi, many protists

• Offspring is DIPLOID (pairs of chormosomes)

ASEXUAL• Production of a new

organism (individual) from a single parent (no fusion of gametes).

• Some animals• Almost all plants• Most fungi, many protists• Bacteria• Offspring is HAPLOID or

DIPLOID

Methods of asexual reproduction:1. Binary fission

Parent cell divides into two new cells of similar size.

Genetically identical “clones” (all DNA the same)

E. Coli bacteria

Parent cell:

Daughter cells:

• Where is the parent cell after division?

• Can bacteria be “immortal” in a way animals cannot?

Methods of asexual reproduction:2. Budding

Budding in Yeast

Production of new organisms (one or more cells) of smaller size than the parent.

Genetically identical “clones” (all DNA the same)

Budding in Hydra

Some other examples of asexual reproduction:

A piece of a plant can grow into a whole, complete plant

by vegetative growth.

Planarian worms can reproduce by fragmentation

and regeneration

There are more methods of asexual reproduction:

Spore production

•One spore can grow into a full, multicellular organism

•Not necessarily clones of each other. Often haploid.

Spores and spore-

containing capsules of

moss

Sexual Reproduction• Two gametes (sperm and egg) fuse to

create a new organism, genetically different from either parent.

Sexual Reproduction• Male and female gametes (sperm and egg)

combine to form a single-celled zygote

• Zygote divides to form an multicellular embryo, which divides and grows into an adult

Sexual Reproduction

Gametes

Zygote

Embryo

Adult

Bill Nye the Science Guy

Click Here for a

Video on Reproduction and Life Cycles

Chromosomes, Cell Cycle,

Mitosis and Meiosis

CHROMSOMES: Long pieces of DNA that contain a lot of genetic information.

Chromosome function

• the genetic information in chromosomes tells how to build and run the organism

DNA is condensed into Chromosomes, but only during cell division, in order to organize it and keep

track of it as it moves to daughter cells

In eukaryotes, the DNA is in multiple, linear chromosomes inside the nucleus.

In prokaryotes, like bacteria, the DNA is in one circular chromosome in the cytoplasm.

Haploid v. Diploid

• Haploid cells (N) have one copy of each chromosome

• Diploid cells (2N) have two copies of each chromosome (one from each parent)

N

+

N2N

The cell cycle—The Life of a Cell

synthesis

Gap 2

Gap 1

Cytokinesis

The cell CycleINTERPHASE:•The cell grows and carries out its typical functions.•The cell also prepares to divide including copying all chromosomes exactly. DNA is relaxed.

MITOSIS: the nucleus divides into two nuclei, each with a complete, genetically identical set of chromosomes (same as the original parent cell.) DNA is condensed.

(bacteria divide by binary fission, not mitosis)

CYTOKINESIS: divides the cytoplasm and plasma membrane of the cell. The cell divides into two cells.

• During interphase each chromosome is copied exactly to make an identical pair.                                 

• A duplicated chromosome is has its two identical copies (sister chromatids) joined by the centromere.

Mitosis• Creates genetically identical cells with a full

set of the parent cell’s chromosomes.– If parent cell is diploid, the new cells are diploid– If parent cell is haploid, the new cells are haploid.

• Used for growth, repair, and asexual reproduction (cloning).

Onion cells in the root zone of division:Which cells are in interphase? Which cells are in mitosis? How can you tell?

AB C

A = interphase (chromosomes relaxed)B = mitosis (chromosomes condensed and splitting into two sets)C = mitosis (chromosomes condensed)

Note the partial cell wall formed along the equator of the cell. This cell is in cytokinesis

What phases of the cell cycle can you find?

Meiosis

• Produces four cells, all genetically unique

• Makes gametes (sperm and egg)

• Used for sexual reproduction only.

• Parent cell is diploid, daughter cells are haploid.

Meiosis: Differences for sperm and egg production

Mitosis v. Meiosis: same start, different products

Produces two genetically identical cells with the same number of chromosomes as the parent cell (haploid or diploid).

Produces four genetically different cells with half the number of chromosomes as the parent cell (haploid).

Humans chromosome number is 2n = 46

• Diploid cells (all body cells except gametes) have 46 chromosomes, with 23 pairs.– 22 pairs with the same genes (autosomes)– 1 pair with different genes (sex chromosomes)

• An individual may have 2 of the same (female, XX) or two different (male, XY).

• Haploid cells (gametes only) have 23 chromosomes– Egg cells carry and X chromosome, sperm cells

carry an X or Y.

Human sex is determined by the X and Y chromosomes

• A female (XX) has two X (and 0 Y) chromosomes. She will pass one a child.

• A male (XY) has one X and one Y chromosome. He will pass either the X or the Y to a child. – Male determines gender: if

the sperm cell delivers an X chromosome, the child will be a girl; if Y, it will be a boy

Sometime chromosomes do not separate properly

• Leads to extra or missing chromosomes

• Most alternate chromosome numbers fail to develop as embryos

• Exceptions are:

– Extra 21 (Trisomy 21, Down’s Syndrome)

– Extra sex chromosomes (XXY, XYY, XXX)

– Missing sex chromosome (X)

– Trisomy 13

Karyotype: a picture of the chromosomes in the cell

• Shows sex (XX or XY)

• Shows chromosome number: normal (46 in humans), extra (47) missing (45).

• Can show major chromosome damage or mutation

Karyotype Practice

Karyotype practice

Karyotype practice

Karyotype Activity

• Go here for practice in karyotyping.