• Every human cell (except 1 type) has 46 chromosomes = Diploid (2n) number.

ReviewReview

Since we don’t want more then 46 chromosomes in our cells, then the gametes must have HALF the normal # of chromosomes= HAPLOID (n)

a little a little more…..more…..•So how do we make these cells?

•Would mitosis work?

•The form of cell division by which gametes, with half the number of chromosomes are produced. •Diploid (2n) haploid (n)

MEIOSIS

• Meiosis is sexual reproduction

• TWO divisions (meiosis I and meiosis II

•Sex cells divide to produce gametes (sperm or egg)

•The new cells are called Haploid, they have half the number of chromosomes

• Meiosis is similar to mitosis with some chromosomal differences

It only happens in the GONADS (testes and ovaries)

Male: Spermatogenesis

Female: Oogenesis

GAMETOGENESGAMETOGENESISIS

OOGENESISOOGENESIS

SPERM

ATO

GEN

ES

SPERM

ATO

GEN

ES

ISIS

• This produces a fertilized egg = Zygote!

Meiosis needs two divisions!

Main difference between mitosis and meiosis:Meiosis produces 4 new gametes! We need 4 gametes every division for

GENETIC VARIATION!

1. Crossing Over Occurs during Prophase I

2. Independent Assortment Occurs during Metaphase I

3. Random Fertilization Sperm joins with the egg cell

Crossing over can occur between “nonsister” chromatids

Segments of the chromatidsbreak and reattach to the otherchromatid

describes how different genes independently separate from one another when reproductive cells develop. the combinations of traits in the offspring do not always match the

combinations of traits in the parent

Assort randomly at the middle of the cell

Non disjunction is the failure of chromosome pairs to separate properly during meiosis stage 1 or stage 2

This could arise from a failure of homologous chromosomes to separate in meiosis I, or the failure of sister chromatids to separate during meiosis II or mitosis. The result of this error is a cell with an imbalance of chromosomes.

Chromatin duplicates

CentriolesINTERPHASEINTERPHASE

• chromatin becomes chromosomes

PROPHASE 1PROPHASE 1

• the nuclear membrane disintegrates

• homologous chromosomes pair up- crossing over may occur

the chromosomes condense

centrioles move to opposite poles of cell & begin making the spindle.

the nuclear membrane breaks down

PROPHASE 1PROPHASE 1

PROPHASE 1PROPHASE 1Homologous chromosomes pair up

…. and crossing over may occur.

PROPHASE 1PROPHASE 1

centrioles begin building the spindle

PROPHASE 1PROPHASE 1

METAPHASE 1METAPHASE 1

Pairs of homologous chromosomes line-up at the center of the cell

Each pair is assortedindependently

So this pair could have assorted like this

METAPHASE 1METAPHASE 1

So this pair could have assorted like this

•Homologous pairs of chromosomes are pulled apart.

ANAPHASE 1ANAPHASE 1

ANAPHASE 1ANAPHASE 1

•Sister chromatids remain attached at the centromere

ANAPHASE 1ANAPHASE 1

•new nuclear membrane forms around each group of chromosomes forming haploid nuclei.

TELOPHASE 1TELOPHASE 1

new nuclear membrane forms around each group of chromosomes

TELOPHASE 1TELOPHASE 1

cytokinesis occurs

TELOPHASE 1TELOPHASE 1

•Now, BOTH haploid cells will begin Meiosis II

CYTOKINESIS 1CYTOKINESIS 1

•in this division, sister chromatids will separate

Meiosis II is very much like Mitosis

• the nuclear membrane breaks down

PROPHASE 2PROPHASE 2

• centrioles move to opposite poles of the parent cell

the nuclear membrane breaks down

PROPHASE 2PROPHASE 2

PROPHASE 2PROPHASE 2

centrioles begin building the spindle

PROPHASE 2PROPHASE 2

PROPHASE 2PROPHASE 2

The doubled chromosomes move to the equator of the cell

METAPHASE 2METAPHASE 2

sister chromatids are pulled apart (like in mitosis)

ANAPHASE 2ANAPHASE 2

ANAPHASE 2ANAPHASE 2

•new nuclear membrane forms around each group of chromosomes

•cytokinesis occurs

TELOPHASE 2TELOPHASE 2

the spindle breaks down

TELOPHASE 2TELOPHASE 2

A new nuclear membrane forms around each group of chromosomes

TELOPHASE 2TELOPHASE 2

• Cytokinesis occurs

• Four different, haploid cells are formed

CYTOKINESIS 2CYTOKINESIS 2

1. Down Syndrome

2. Turner’s Syndrome

3. Klinefelter’s Syndrome

Trisomy: having an extra or 3rd chromosome Many down syndrome cases can be identified

by having an extra chromosome

Women and girls with turner’s, have only one X chromosome

This is an example of monosomy

Symptoms include lack of ovarian development, short stature, webbed neck, arms that turn slightly at the elbow

Men and boys with Klinefelter have a Y chromosome and 2 X chromosomes.

This is an example of trisomy Men and boys are usually

tall, and lack secondary sex characteristics such as underarm and facial hair

Diploid – number of chromosomes in a somatic cell- 46

Haploid/ monoploid- number of chromosomes in a gamete- 23

Homologous chromosome- same size and shape

Gametes- reproductive cells- sex cells Zygote- the first cells as a result of

fertilization of the egg and sperm cell- has a diploid number of chromosomes

Gonads- the organs that make gametes

GeneSegment of DNA that controls the production of proteins

Enzymetype of protein in all living things that

changes the rate of reactions Production of enzymes is directed by genes

Cyclin protein that controls the cell cycle and is

activates the enzymes

How?

Failure to produce enzymes Overproduction of enzymes Production of the wrong enzyme

-What can happen?- Cancer: a malignant growth resulting from

uncontrolled cell division.

Results from changes in genes that control the cell cycle

Malignant TumorMass of cancerous cells, can deprive normal

cells of nutrients

Metastasis Cancer cells spread through bloodstream to

other organs of the body

Causes GeneticsEnvironmental factors ( where you live,

cigarette smoke, UV radiation, viral infections)

PreventionHealthy lifestyleDiet, avoiding alcohol, drugs, smokingProtecting from the sunCancer screening (pap smear, colonoscopy,

mammogram)

Embryonic stem cells: unspecialized cells that have the potential to become a wide variety of specialized cells.Produce every tissue in the bodyFound in embryos

Adult Stem Cells-found in the umbilical cord and bone marrow.- can produce some different types of cells but

not all Example: bone marrow stem cells can only

produce different types of blood cells.

Cures for diseases

Reverse paralysis caused by spinal cord injury

Organ regeneration