1. Meiosis and Sexual Reproduction

2. I. Meiosis
Meiosis is a special type of cell division that produces haploid cells. It only occurs in the gametes (sex) forming cells of the male and female organism. When the gametes unite at fertilization, the original chromosome number for that organism is restored in the new individual.
The formation of gametes is essential to the continuation of a species. This special process of gamete formation from diploid cells is called meiosis. The cells produced in this process have half (haploid) the number of chromosomes than the original cells. There are 2 divisions in this process. Male and female meiosis processes are different in the number of cells produced. Crossing over and swapping of genetic information can occur during Prophase I of this process.

3. State Test Question
In order for humans to have a normal number of chromosomes, sex cells must be—
haploid.
diploid.
triploid.
tetraploid.

4. State Test Question What is the primary purpose of meiosis?
Production of haploid somatic cells
Production of diploid gametes
Production of proteins
Production of haploid gametes

5. State Test Question Unlike mitosis, meiosis occurs only in—
reproductive cells.
muscle cells.
connective tissue cells.
nerve cells.

7. State Test Question
What structures carry the MOST genetic information for a leaf cell?
Chromosomes
Ribosomes
Centrioles
Chloroplasts

8. Somatic Cell- Any “body” cell other than a sperm or egg cell.
Autosome- A chromosome found in a cell that is NOT a sex determining chromosome.
Sex Chromosome- A chromosome that determines the organism’s sex—male or female. XX= female and XY= male.
Egg- The sex cell formed in the female by meiosis.
Sperm- The sex cell formed in the male by meiosis.
Fertilization- Union of egg and sperm to form a new individual organism.
Zygote- A fertilized cell. A diploid cell that results from the union of egg and sperm.
Sex Chromosomes
Zygote
Somatic Cell (Liver Cell)
Egg, Sperm, Fertilization

9. The cell division in which 1 diploid (2n) cell produces 4 haploid (n) cells called sex cells or gametes, which have half the number of chromosomes as a body cell of the parent cell. During meiosis, the chromosome number is reduced by one half and gametes are formed.
Occurs in the reproductive organs, the ovaries in females, and the testes in males.
The gametes are ova, or eggs, in females, and sperm in males.
The union of the egg and the sperm is called fertilization and produces a zygote.
A sex cell begins meiosis with the diploid number (2n=46) of chromosomes in humans. The cell undergoes two divisions, but the chromosomes are duplicated only once. The two divisions result in four daughter cells, each having one half the number of chromosomes of the parent cell (haploid number or n=23 chromosomes in humans.)

10. Unlike body/somatic cells which contain 46 chromosomes (2n), the sex cells each contain 23 (n) chromosomes, so when fertilization occurs, the zygote will have 46 chromosomes.
Egg (23) + Sperm (23) → Zygote (46)
**If a gamete contained the 2n number of chromosomes, fertilization would result in a zygote with twice the diploid number, or 92 chromosomes and not viable (not being able to survive).
Humans have 23 pairs of chromosomes. One pair are the sex chromosomes.

11. State Test Question
Sexual reproduction in plants depends on sex cells being produced by the process of—
osmosis.
fermentation.
transpiration.
meiosis.

12. Formation Of Egg And Sperm
Oogenesis
The formation of the egg cells in females occurs in the ovaries.
Produces 1 viable egg cell and 3 polar bodies.
Spermatogenesis
The formation of the sperm cell in males occurs in the testes.
Produces 4 viable sperm cells

13. Spermatogenesis
Oogenesis

14. Meiosis has two divisions:
In meiosis a spindle forms and cytoplasm divides in the same way as occurs in mitosis, but what happens to the chromosomes in meiosis is very different.
Meiosis has two divisions:
Meiosis I—Meiosis I begins with 1 diploid (2n) cell.
Meiosis II—By the end of Meiosis II, there are four haploid (n) cells.

15. During Interphase that precedes Meiosis I, the cell also replicates its chromosomes (DNA). Each chromosome then consists of two identical sister chromatids, held together by a centromere. So, meiosis starts with homologous chromosomes (homologous chromosomes are similar in size, shape, and genetic content.)

16. * (on the following slides) These are unique steps to
Meiosis I:
There are four phases of Meiosis I:
Prophase I
Metaphase I
Anaphase I
Telophase I
* (on the following
slides) These are
unique steps to
meiosis. They do not occur in
mitosis

17. 1. Prophase I
*Step 1—The chromosomes (DNA) coil up becoming visible and a spindle forms. The nuclear membrane and nucleolus disappear.
*Step 2— Synapsis occurs
Synapsis is the pairing of homologous chromosomes.
A tetrad is formed.
A tetrad is the pair of homologous chromosomes.
**Crossing over can occur here.
Crossing over is the exchange of genetic material. This allows for genetic variation among organisms.

18. 2. Metaphse I
Tetrads are moved by spindle fibers to the equator.
**They line up in homologous pairs. In mitosis, they line up independently.

19. 3. Anaphase I
Homologous chromosomes separate, chromosomes of each pair move to opposite poles.
**The chromatids do not split as in mitosis.

20. 4. Telophase I
Chromosomes gather at the poles of the cell. The cytoplasm divides.
**Each cell has 1 homologous pair. These chromosomes are still attached by centromeres forming two daughter cells.
Another cell division is needed because each chromosome is still doubled, containing two identical sister chromatids.

21. Meiosis II
Meiosis II is similar to mitosis in that the chromatids separate.
There are four phases of Meiosis II:
Prophase II –A new spindle forms around the chromosomes.
Metaphase II-Pairs move to the equator of the cell.
Anaphase II-Sister chromatids separate and move to opposite poles.
Telophase II-Spindle fibers
dissolve, nuclear membrane
forms, and the cytoplasm
divides.

23. At the end of Meiosis II, 4 haploid cells (n=23) have been formed from the original diploid cell (2n=46)
Mitotic Cell Division
Meiotic Cell Division

24. State Test Question
During which phase of the process pictured below is DNA replicated?
Prophase II
Metaphase II
Anaphase II
Telophase II and Cytokinesis II

25. 23 = 46 + 23
Fertilization =
When a sperm fertilizes an egg, the zygote once again has the diploid number of chromosomes. It can then develop by mitosis into a multicellular organism.
Zygote→tissue→organ→organ systems→organism
Egg
Zygote
Sperm
(1 cell)

26. State Test Question
Human cells have 46 total chromosomes in 23 pairs. Which of the following represents the changes in chromosome number through the stages of meiosis?
Which of the following is a characteristic of asexual reproduction?
Offspring identical to a single parent
Unique haploid gametes
Unique offspring from two parents
Crossing over during synapsis

27. State Test Question
Meiosis is different from mitosis because meiosis produces—
consistent genetic makeup of all gametes.
larger daughter cells.
two gametes for every original parent cell.
cells with half the number of chromosomes.

28. State Test Quesiton
The number of chromosomes in the egg of a potato plant is 24. The number of chromosomes in the cells of the potato root is— 12 24 36 48

29. State Test Question
A species with 12 chromosomes in each somatic cell will produce sex cells with—
A. 3 chromosomes.
B. 4 chromosomes.
C. 6 chromosomes.
D. 24 chromosomes

30. State Test Question
What is a primary difference between mitosis and meiosis?
Mitosis involves two cell divisions, and meiosis involves only one.
Mitosis produces diploid cells, while meiosis produces haploid cells.
Interphase and DNA replication occur only in mitosis.
There is no difference between the two processes.

31. State Test Question The purpose of meiosis is—
production of haploid gametes.
asexual reproduction of unicellular organisms.
duplication of diploid cells.
production of diploid gametes

32. State Test Question The final products of meiosis are— haploid cells.
diploid cells.
triploid cells.
polypoid cells.

33. II. Reproduction There are two types of reproduction:
Sexual Reproduction
Asexual Reproduction

34. 1. Sexual Reproduction
Two parents are involved, each contributing a sex cell, or gamete.
The production of offspring through meiosis.
Gametes (egg & sperm – haploid cells) fuse to produce a diploid zygote, which then develops into a new organism.
During meiosis, members of a pair of chromosomes tend to exchange genetic material before they separate. As a result, sex cells contain different sets of chromosomes and genes. The union of a sperm
cell and an egg cell will produce
gene combinations that differ from
those of the parents. Sexual repro-
duction allows the recombination of
genetic information.

35. 2. Asexual Reproduction
The production of offspring from 1 parent, without the union of gametes.
Offspring are identical to parent (identical genetic makeup.) An individual produced by asexual reproduction is a clone. A clone is an organism that is genetically identical to its parents.
Only mitotic cell divisions occur in asexual reproduction.
Methods of Asexual Reproduction in monerans (bacteria), protests, fungi, and plants include binary fission, budding, and spore formation. The advantage for bacteria producing by binary (asexual reproduction) is that it can be done so fast. Ex: E. coli can produce “1 million” new cells in 7 hours!!! Asexual reproduction allows organisms to produce many offspring in a short period of time.

36. State Test Question
Meiosis results in greater genetic variation than asexual reproduction because it—
is a lengthy process full of errors.
results in a greater number of offspring.
is more common in higher order species.
allows the recombination of genetic information.

37. Binary fission in an amoeba

38. Binary fission in Bacteria
1st DNA is copied so that each new cell will have a copy of the genetic information.
2nd The bacterium or amoeba is pinched into 2 independent cells

39. Budding in yeast
New individuals split off from existing ones. The bud may break from the parent and become an independent organism

40. State Test Quesiton
Compared to sexual reproduction, asexual reproduction results in a—
greater variation in offspring.
larger number of identical cells.
longer life span of a cell.
fewer number o cells dividing

41. State Test Question
What are two sources of genetic variation associated with sexual reproduction?
Binary fission and budding
Mitosis and meiosis
Crossing over and independent assortment
Diploid gametes and DNA replication

42. State Test Question
Bacteria cells reproduce by binary fission, a type of asexual cell division. One advantage of binary fission is—
greater genetic variation in daughter cells.
the ability to reproduce quickly.
greater resistance to disease.
the ability to live under anaerobic conditions.

43. State Test Question
The primary difference between sexual and asexual reproduction is—
asexual reproduction occurs only in multicellular organisms.
asexual reproduction requires a multicellualr parent and a single-celled parent.
sexual reproduction combines DNA from parent cells.
sexual reproduction occurs in only single-celled organisms.

44. State Test Question
According to the graph, one reason that more of the Animal A population survived is because sexual reproduction produces—
individual variation within a population.
larger numbers of viable
offspring.
more female individuals than male.
different forms for each generation.