Happy Friday!Please do the following:• pick up the handouts

• get a chrome-book and get out your Oreo Mitosis lab – you have 15 minutes to submit your video link

https://www.youtube.com/watch?v=gwcwSZIfKlM

REPRODUCTION

All living things can reproduce themselves:• Asexual reproduction• Sexual reproduction

Asexual reproduction occurs when a single organism produces offspring on its own.

The prefix a- means without.

This produces offspring that are genetically identical to their parents.

REPRODUCTION

REPRODUCTION

Sexual reproduction begins with the sperm

and egg…but where did the sperm and egg

come from?

Where it all began…You started as a cell smaller than a period at the end of a sentence…

Zygote

How did you get from a

single zygote to

100 trillion cells?

And now look at you…

Answer: MitosisWhat is mitosis? a parent cell creates two

genetically identical daughter cells

Why is cell division important? Growth Repair

amoeba

MitosisWhich cells undergo mitosis? Somatic cells aka

regular body cells Skin cells Fingernail cells Bone cells

amoeba

Somatic cells contain 2 complete sets of chromosomes. That makes somatic

cells DIPLOID (2n)

You have 2 sets of chromosomes

• 1 set of chromosomes came from your mother (n)

• 1 set of chromosomes came from your father (n)

• Chromosomes are found in homologous pairs (two of each chromosome – 2n)

DIPLOID

REPRODUCTION

Sexual reproduction occurs when two organisms share genetic material to create offspring.

This creates offspring that are different from both parents & genetically unique.

+

Typical Human Family Tree

During sexual reproduction, organisms must share their chromosomes without adding or

subtracting from the total number.

This means that they must create special haploid cells with only one of each

chromosome for sexual reproduction.

MeiosisCreating Haploid Cells

12

• Meiosis is:–Cell division that halves the # of

chromosomes –The process that germ cells go through

to produce gametes (sperm & egg) –Fundamental basis of sexual

reproduction

• Diploid (2n) Haploid (n)

What is Meiosis?

The zygote is a unique genetic mixture of both

parents.

• Meiosis must reduce the chromosome number by half

• Fertilization then restores the 2n number from mom from dad child

meiosis reducesgenetic content

toomuch!

The right number!

Meiosis Forms Haploid Gametes

Meiosis – 2 Cell Divisions

QUESTION:• A cell containing 20 chromosomes

(diploid) at the beginning of meiosis would, at its completion, produce cells containing how many chromosomes?

16

10 chromosomes (haploid or 1n)

• daughter cells contain half the number of chromosomes as the parent cell

• produces gametes (sperm & egg)

• occurs in the testes in male

• occurs in the ovaries in females

Facts About Meiosis

GENE RECOMBINATIONA pair of the same chromosomes, one from mom and one from dad, get blended together to form a single chromosome that is a mixture of both parents DNA.

This creates offspring that are similar to both parents, but genetically unique.

Increasing the genetic variations in a population is an important role of meiosis.

Meiosis does not create new genes; however, it creates new combinations of genes.

Genetic variations are increased even further through the process of crossing over.

Homologous chromosomes recombine to create new gene combinations.

• Homologous chromosomes in a tetrad cross over each other

• Pieces of chromosomes or genes are exchanged

• Produces Genetic recombination in the offspring

CROSSING OVER

The Significance of Meiosis

Meiosis helps create genetically unique offspring.

Meiosis reduces the number of chromosomes to create haploid gamete cells.

Meiosis increases genetic variations and creates new combinations of genes.

Monosomy Trisomy

Is there anything that can go wrong during meiosis?

• Yes!• It is called nondisjunction.

– Chromosomes don’t separate properly and some gametes end up with too many or not enough chromosomes.

Mutations

Only mutations that occur in gamete cells are passed on to the organisms offspring. Mutations to gamete cells usually occur

during the process of meiosis.

sperm

egg

Chromosomal mutations are typically the result of

mistakes that occur when chromosomes cross-over.

Mitosis

makes genetically unique cells

makes genetically identical cells

allows asexual reproduction

allows sexual reproduction

new cells have full set of chromosomes (diploid)

new cells have half set of chromosomes (haploid)

Meiosis

LET’S REVIEW

number of divisions – 1 number of divisions – 2

makes 4 daughter cells makes 2 daughter cells

occurs in somatic cellsoccurs in germ cells