Notes: Types of Reproduction

***Key Idea: Genetic information is passed from parents to offspring through CHROMOSOMES. Remember that chromosomes are DNA and PROTEIN. We have to get the chromosomes from the parent cell the new cells that are being produced.

In ASEXUAL reproduction, ONE organism divides in two and makes an EXACT COPY of itself. This is essentially MITOSIS.

Ex. Budding in yeast Ex. Amoebas Pros : NO ENEGY used to get together with

another organism. Cons : Only ONE parent contributes genes.

Sexual Reproduction: Meiosis

In SEXUAL reproduction, TWO organisms must

come together to create an offspring that is genetically DIFFERENT than either parent.

Pros : Genes from BOTH parents contribute to

offspring. Cons : Must USE ENERGY to get together with

another organism.

To reproduce sexually, the organisms must first form “gametes.” Cells of the body have two copies of sets of chromosomes. Gametes only have one set. Why?

DIPLOID cells have two sets of chromosomes. We represent

this as 2n. HAPLOID cells have one set of chromosomes. We represent

this as n.

Haploid

Diploid

In humans, the MALE gamete is the SPERM. The FEMALE gamete is the EGG. The sperm swims up the female reproductive tract and

FERTILIZES the egg. The egg and sperm together is called a ZYGOTE The ZYGOTE then divides by MITOSIS to form a multicellular

(many-celled) organism. Mitosis is just plan old cell division.

Egg and Sperm!

Fertilization

Fertilization

The process of forming a gamete is called MEIOSIS.

Steps of Meiosis

1) Replication2) Pairing up of homologous chromosomes.3) First division4) Second division

Mitosis MeiosisCell divides once. You get two cells identical to the original. Each have two copies of each chromosome

Two cell divisions. You get four cells that are genetically different than the original cell. Each have one copy of each chromosome.

2) Pairing up of homologous chromosomes.

o HOMOLOGOUS CHROMOSOMES are both sets of chromosomes.o Ex. Both copies of chromosome 12

o ***Genetic material is exchanged or shuffled between the homologous chromosomes in a process called CROSSING OVER. This produces the NEW combinations of traits that were not seen in either parent.

Homologous Chromosomes

Homologous ChromosomesCrossing Over!

3) First division- Result is two haploid cells with replicated chromosomes.

4) Second division- Result is 4 haploid cells with

unreplicated chromosomes. (Result is the egg or sperm).

Mitosis (asexual)

Meiosis (sexual)

# of divisions 1 2# of cells produced 2 4sets of chromosomes in cells produced

2 (cells are diploid or 2n)

1 (cells are haploid or “n”)

type of cells it occurs in

all cells reproductive tissues only

homologous chromosomes pair up?

no yes

genetic variety of offspring

same as parent cell

genes are shuffled during crossing over, genetic variety is increased

Mitosis MeiosisCell divides once. You get two cells identical to the original. Each have two copies of each chromosome

Two cell divisions. You get four cells that are genetically different than the original cell. Each have one copy of each chromosome.