1. 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

2. REPRODUCTION All living things can reproduce themselves:
Asexual reproduction
Sexual reproduction

3. 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.

4. REPRODUCTION
Sexual reproduction begins with the sperm and egg…but where did the sperm and egg come from?

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

6. How did you get from a single zygote to 100 trillion cells?
And now look at you…
How did you get from a single zygote to 100 trillion cells?

7. Answer: Mitosis What is mitosis? Why is cell division important?
amoeba
What is mitosis?
a parent cell creates two genetically identical daughter cells
Why is cell division important?
Growth
Repair
Unicellular organisms
Cell division = reproduction
Reproduces entire organism& increase population
Multicellular organisms
Cell division provides for growth & development in a multicellular organism that begins as a fertilized egg
Also use cell division to repair & renew cells that die from normal wear & tear or accidents

8. Mitosis Which cells undergo mitosis?
amoeba
Which cells undergo mitosis?
Somatic cells aka regular body cells
Skin cells
Fingernail cells
Bone cells
Somatic cells contain 2 complete sets of chromosomes.
That makes somatic cells DIPLOID (2n)
Unicellular organisms
Cell division = reproduction
Reproduces entire organism& increase population
Multicellular organisms
Cell division provides for growth & development in a multicellular organism that begins as a fertilized egg
Also use cell division to repair & renew cells that die from normal wear & tear or accidents

9. 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

10. REPRODUCTION
Sexual reproduction occurs when two organisms share genetic material to create offspring.
This creates offspring that are different from both parents & genetically unique. +

11. 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.

12. Creating Haploid Cells
Meiosis
Creating Haploid Cells 12 12

13. The zygote is a unique genetic mixture of both parents.
What is Meiosis?
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)
The zygote is a unique genetic mixture of both parents. 13

14. Meiosis Forms Haploid Gametes
Meiosis must reduce the chromosome number by half
Fertilization then restores the 2n number
from mom
from dad
child
too
much!
meiosis reduces
genetic content
The right number!

15. Meiosis – 2 Cell Divisions15

16. Question: 10 chromosomes (haploid or 1n)
A cell containing 20 chromosomes (diploid) at the beginning of meiosis would, at its completion, produce cells containing how many chromosomes?
10 chromosomes (haploid or 1n) 16

17. Facts About Meiosis
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 17

18. Gene Recombination This creates offspring that are similar to
A 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.

19. 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.

20. Homologous chromosomes recombine to create new gene combinations.
Genetic variations are increased even further through the process of crossing over.
Homologous chromosomes recombine to create new gene combinations.

21. CROSSING OVER Homologous chromosomes in a tetrad cross over each other
Pieces of chromosomes or genes are exchanged
Produces Genetic recombination in the offspring

22. 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.

23. 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.
Monosomy
Trisomy

24. Mutations
sperm
egg
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.

25. Chromosomal mutations are typically the result of mistakes that occur when chromosomes cross-over.

26. Let’s review Mitosis Meiosis makes genetically unique cells
makes genetically identical cells
allows asexual reproduction
allows sexual reproduction
occurs in somatic cells
occurs in germ cells
new cells have full set of chromosomes (diploid)
new cells have half set of chromosomes (haploid)
number of divisions – 1
number of divisions – 2
makes 4 daughter cells
makes 2 daughter cells 26