Types of Reproduction Notes

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.

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.

oHOMOLOGOUS CHROMOSOMES are both sets of chromosomes.oEx. 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

# of cells produced

sets of chromosomes in cells produced

type of cells it occurs in

homologous chromosomes pair up?

genetic variety of offspring increased

1 2

2 4

2n nall cells reproductive tissues

only

NO yes

NO YES

Mitosis Here are the two chromosome #5s in a 2n (diploid cell).

Replication occurs. Each chromosome is copied to prepare for division.

Homologous chromosomes DO NOT pair. All chromosomes line up in the middle of the cell “single file.” The cell division occurs.

The replicated chromosomes are separated.

The product is 2 cells that are diploid (2n). This is exactly what we started with.

Meiosis Here is one set of chromosomes. For example, the two sets of chromosome #5. We call the two sets “homologous chromosomes.” This is a diploid (2n) cell.

Replication occurs. Each chromosome is copied to prepare for division.

The first division occurs. Homologous chromosomes separate.

We now have haploid (n) cells with replicated chromosomes.

We now have 4 haploid (n) cells with unreplicated chromosomes.

The second division occurs and the replicated chromosomes separate.

MeiosisMitosis

REPLICATION

REPLICATION

2n diploid cell

2n diploid cell

Chromosomes line up single file in middle of cell.

Homologous chromosomes pair and line up “two by two.” Crossing over occurs to increase genetic variety.FIRST DIVISION

Haploid (n) cells with replicated chromosomes.

SECOND DIVISION

DIVISION

4 haploid (n) cells with unreplicated chromososomes