1. Unit 3: Cell Division Left Side Pg Right Side Unit Page 48
Table of Contents 49
Flow Map – Cell Cycle 50
C.N. – The Cell Cycle 51
Brace Map – Meiosis 52
C.N. – Meiosis 53

2. Unit 3: Cell Division Chapter 11-4
Meiosis
Unit 3:
Cell Division
Chapter 11-4

3. Learning Goals 1. Describe the overall process of meiosis.
2. Define homologous chromosomes and explain diploid and haploid.
3. Explain crossing over, its importance, and during which step it occurs.
4. Describe the two types of gamete formation and how fertilization occurs.

4. Meiosis
A process of cell division that creates gamete cells, or non-identical cells with half the number of chromosomes
The gametes from a male and a female combine in sexual reproduction to make a new individual

5. Homologous Chromosomes
Each cell has 2 sets of chromosomes
Homologous Chromosomes = a pair of chromosomes that have the same genes at the same locations
1 came from mom
1 came from dad

6. Homologous chromosomes
From mom
From dad

9. Chromosome Number
Diploid (2n): cells that have 2 sets of homologous chromosomes (2n)
Human body cells are diploid (46 chromosomes or 23 pairs)
Haploid (n): cells that have 1 set of chromosomes (n)
sex cells (gametes) are haploid
human haploid cells (egg & sperm) have 23 chromosomes total

10. 1) A bug has a haploid number n=5. What is the diploid number (2n)?
2) A crocodile has a diploid number 2n=50. What is the haploid number (n)?
meiosis
Haploid gamete
Diploid 2n n n

11. Human Female Karyotype

12. Human Male Karyotype

13. Down Syndrome Female
Trisomy

14. Meiosis Overview
A type of cell division specific to sexual reproduction (two parent cells)
Cells (diploid) divide twice resulting in 4 daughter cells (haploid)
Each cell has half the number of chromosomes as the original cell
Each new cell is genetically different

15. Steps of Meiosis

16. Interphase DNA is copied before the start of Meiosis I.
This makes 2 identical sister chromatids
They have the same genes at the same locations.

17. Homologous chromosomes vs. sister chromatids
From mom
From dad

18. Meiosis 1
Four steps:
Prophase 1
Metaphase 1
Anaphase 1
Telophase 1

19. Prophase 1
The homologous pairs of chromosomes come together and line up side by side. (tetrad = 4)

20. Crossing-over
Homologous chromosomes can Cross-over and exchange a portion of the chromosome (DNA) at random

21. Crossing-over is very important in meiosis because it creates genetic variation (new combinations of genes), which makes us all different.
This is why you do not look exactly like your siblings.

22. Crossing over happens randomly.
However, some genes are linked, or close together on the chromosome, meaning they are more likely to be inherited together.
Red hair
Freckles
Chromosome 16

23. After crossing-over, the homologous chromosomes separate & the cells divide

24. Meiosis II
Four steps:
Prophase 2
Metaphase 2
Anaphase 2
Telophase 2

25. Sister chromatids separate & the cells divide.
Result is 4 genetically different haploid daughter cells

26. Principal of Independent Assortment
Genes for different traits can segregate (separate) independently during the formation of gametes.
Independent assortment and crossing-over account for the many genetic variations observed in plants, animals, and other organisms.

27. Assume there was only one cross-over in a man’s sperm and one cross-over in a woman’s egg, they have the possibility of producing 4,951,760,200,000,000,000,000,000,000 genetically different children

28. Gamete Formation Gametes = Sex Cells (eggs & sperm) Spermatogenesis:
In males meiosis occurs in the testes
produces 4 sperm 23 23 23 23

29. Spermatogenesis

30. Oogenisis: In females meiosis occurs in the ovaries
produces only 1 egg and 3 polar bodies
Egg 23
Polar Bodies

31. Oogenesis

32. First cell of a new organism
Fertilization: the fusion of haploid sex cells
Zygote 46 23
First cell of a new organism

33. Only one sperm and one egg come together
The first sperm to reach the egg will be the one to fertilize it.

34. Comparing Mitosis & Meiosis
Mitosis results in the production of 2 genetically identical diploid cells.
Meiosis produces 4 genetically different haploid cells.

36. Learning Goals 1. Describe the overall process of meiosis.
2. Define homologous chromosomes and explain diploid and haploid.
3. Explain crossing over, its importance, and during which step it occurs.
4. Describe the two types of gamete formation and how fertilization occurs.