1. Reproduction of Sex Cells
Meiosis
Reproduction of Sex Cells

4. Structure
Function
Plasma membrane
Surrounds cell, controls entry and exit
Golgi apparatus
Packages and arranges transport for proteins outside of the cell
Free ribosomes
Produce proteins for use inside the cell
Nuclear membrane
Surrounds the nucleus, controls entry and exit
Nucleus
Contains DNA (genetic information)
Lysosome
Breakdown molecules within the cell
Mitochondria
Site of respiration (chemical reaction to release energy – basic metabolic reaction)
Cytoplasm
’cell sap’ or ‘gel like’ substance
Rough endoplasmic reticulum
Produces protein for use outside of the cell

5. Cells have a life cycle
There are two types of cells: Body cells and Sex cells
Normal body cells reporoduce using a process called mitosis
Sex cells reproduce using a process called meiosis

6. Meiosis Introduction
Meiosis is part of the life-cycle of every organism that reproduces sexually.
Meiosis is cell division that produces sex cells ( sperm and eggs), also called gametes

7. Gametes
Each gamete contains half the number of chromosomes of the parent.
Because they only have half the chromosomes of non-sex cells we call gametes haploid.

8. Gametes
During the fertilization stage of sexual reproduction, the male gamete (sperm) fuses with the female gamete (egg) to produce a zygote with two sets of chromosomes.

9. Why is this important?
The chromosomes in the gametes contain genes from the parents that will determine the characteristics of the zygote (baby).

10. Why is the important? Genes are the units of heredity
Genes are segments of DNA
Each gene has a specific location on a certain chromosome

11. Why is the important?
One set of chromosomes is inherited from each parent
Reproductive cells called gametes (sperm and eggs) unite, passing genes to the next generation

12. Sexual vs. Asexual Reproduction
In asexual reproduction, one parent produces genetically identical offspring by mitosis
In sexual reproduction, two parents give rise to offspring that have unique combinations of genes inherited from the two parents

13. Haploid vs. Diploid
Non-sex cells (most cells) contain two sets of each type of chromosome.
A cell that has two full sets of chromosomes is called diploid.

14. Pair of homologous
chromosomes
5 µm
Centromere
Sister
chromatids

15. Homologous Chromosomes
In diploid cells, each pair of chromosome has the same genes (example = gene for eye color).

16. Homologous Chromosomes
However, they do NOT usually have the same alleles (variation of gene = gene for blue eyes).
The pairs of NOT identical, but they are homologous.

17. Human Chromosomes Sex Chromosomes
The sex chromosomes are called X and Y

18. Human Chromosomes
Human females have a homologous pair of X chromosomes (XX)
Human males have one X and one Y chromosome

19. Human Chromosomes
Each pair of homologous chromosomes includes one chromosome from each parent
The 46 chromosomes in non-sex human cell are two sets of 23: one from the mother and one from the father

20. Human Chromosomes
The number of chromosomes in a single set is represented by n
A cell with two sets is called diploid (2n)
For humans, the diploid number is 46 (2n = 46)

21. Human Sex Cells
Gametes are haploid cells, containing only one set of chromosomes
For humans, the haploid number is 23 (n = 23)
Each set of 23 consists of 22 autosomes and a single sex chromosome

22. Human Sex Cells In an unfertilized egg (ovum), the sex chromosome is X
In a sperm cell, the sex chromosome may be either X or Y – father cells determine gender.

23. Sexual Reproduction -- Fertilization
At sexual maturity, the ovaries and testes produce haploid gametes
Gametes are the only types of human cells produced by meiosis, rather than mitosis
Meiosis results in one set of chromosomes in each gamete
Fertilization, the fusing of gametes, restores the diploid condition, forming a zygote
The diploid zygote develops into an adult

24. Key
Haploid (n)
Diploid (2n)
Haploid gametes (n = 23)
Ovum (n)
Sperm
cell (n)
Testis
Ovary
Mitosis and
development
Multicellular diploid
adults (2n = 46)
FERTILIZATION
MEIOSIS
Diploid
zygote
(2n = 46)

25. Process of Meiosis.
The number of chromosomes are reduced from diploid to haploid in the process of meiosis.

26. Overview of Meiosis
By the end of meiosis , the diploid cell that entered meiosis has become 4 haploid cells.

28. Telophase II and Cytokinesis
Phases of Meiosis
Meiosis II
Telophase I and Cytokinesis I
Metaphase II
Anaphase II
Telophase II and Cytokinesis
Prophase II

29. Formation of sperm by Meiosis

30. Formation of Egg Cells by Meiosis
In many female animals, only one egg results from meiosis. The other three cells, called polar bodies, are usually not involved in reproduction

31. Variation
The behavior of chromosomes during meiosis and fertilization is responsible for most of the variation that arises in each generation
Two mechanisms contribute to genetic variation:
Independent assortment of chromosomes
Random fertilization

32. Independent Assortment of Chromosomes.
In independent assortment, each pair of chromosomes sorts maternal and paternal homologues into daughter cells independently of the other pairs
The number of combinations possible when chromosomes assort independently into gametes is 2n, where n is the haploid number
For humans (n = 23), there are more than 8 million (223) possible combinations of chromosomes

33. Independent Assortment

34. Random Fertilization
Random fertilization adds to genetic variation because any sperm can fuse with any ovum (unfertilized egg)
The fusion of gametes produces a zygote with any of about 64 trillion diploid combinations
Each zygote has a unique genetic identity

35. Dragon Meiosis
Step 1: Cut out ONE set of 14 chromosomes

36. Dragon Meiosis
Step 2: Flip the 14 chromosomes over so that you canNOT see the letters

37. Dragon Meiosis Step 3: Randomly pick 7 chromosomes ONE OF EACH SIZE.
After you have picked 7, throw other 7 chromosomes in the recycling bin.

38. Dragon Meiosis
Step 4: Flip the Chromosomes over and write down the letters on your worksheet.
BLUE is for MALES & PINK IS FOR FEMALES.
You have just simulated Random Assortment of Chromosomes
Male Gene (1st color)
Female Gene (2nd color)

39. Dragon Meiosis
Step 5: Flip the Chromosomes over and write down the letters on your worksheet.
BLUE is for MALES & PINK IS FOR FEMALES.
You have just simulated Random Assortment of Chromosomes
Male Gene (1st color)
Female Gene (2nd color)

40. Dragon Meiosis
Step 6: Now write down the letters of your partners chromosomes. These 2 sets of chromosomes will fuse in the nucleus of the new baby dragon, and form its genetic make-up and determine its characteristics.
You are simulating Random FERTILIZATION.
Male Gene (1st color)
Female Gene (2nd color)

41. Dragon Meiosis
Step 7: Now write the genotype (the letters) of your new baby dragon in the other table in your worksheet.
Notice that your baby dragon get one chromosome from mom and one chromosome from dad.
Because your baby dragon has two sets of chromosomes it is diploid.
Trait
Genotype
Phenotype
Fire/No fire (A/a’s)
Toes (M/m’s)
Spikes on tail (Q/q’s)
Tail color (T/t’s)
Body color (E/e’s)
Wing color (L/l’s)
Horn/no horn (D/d’s)
(D/d’s)

42. Dragon Meiosis Step 9: Determine the phenotype of your baby dragon.
Phenotype is its physical appearance.
Use the chart on the other worksheet
Trait
Genotype
Phenotype
Fire/No fire (A/a’s)
Toes (M/m’s)
Spikes on tail (Q/q’s)
Tail color (T/t’s)
Body color (E/e’s)
Wing color (L/l’s)
Horn/no horn (D/d’s)
(D/d’s)

43. Dragon Key

44. Dragon Meiosis Step 10: Draw your dragon & answer the question.
Turn in by the end of the period.
Pick up Meiosis Webquest and Reading Question worksheet

45. HOMEWORK